UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Unbalanced magnetrons Clarke, Glenn A. 1990

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1990_A7 C52.pdf [ 4.27MB ]
Metadata
JSON: 831-1.0074522.json
JSON-LD: 831-1.0074522-ld.json
RDF/XML (Pretty): 831-1.0074522-rdf.xml
RDF/JSON: 831-1.0074522-rdf.json
Turtle: 831-1.0074522-turtle.txt
N-Triples: 831-1.0074522-rdf-ntriples.txt
Original Record: 831-1.0074522-source.json
Full Text
831-1.0074522-fulltext.txt
Citation
831-1.0074522.ris

Full Text

UNBALANCED MAGNETRONS by GLENN A. CLARKE B.Sc,  Queens U n i v e r s i t y ,  1988  THESIS SUBMITTED IN PARTIAL FULFILLMENT THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE  in THE FACULTY OF GRADUATE STUDIES ENGINEERING PHYSICS We accept t h i s t h e s i s as conforming t o the r e q u i r e d  standard  THE UNIVERSITY OF BRITISH COLUMBIA September 1990 ° Glenn A. C l a r k e ,  1990  In presenting  this  degree at the  thesis  in  University of  freely available for reference copying  of  department  this or  publication of  partial fulfilment  of  British Columbia,  I agree  and study.  his  or  her  Department The University of British Columbia Vancouver, Canada  DE-6 (2/88)  that the  representatives.  may be It  is  this thesis for financial gain shall not be  permission.  Date  requirements  I further agree  thesis for scholarly purposes by  the  that  for  an  advanced  Library shall make it  permission for extensive  granted  by the  understood  head  that  allowed without  of  my  copying  or  my written  ABSTRACT  In r e c e n t y e a r s the 'unbalanced* magnetron s p u t t e r source has been shown t o be an important advancement f o r a p p l i c a t i o n s requiring coatings  ion-assisted, and  optical  thin  film  multilayers  deposition. a r e examples  Diamondlike of  coatings  which can be s i g n i f i c a n t l y improved by i o n bombardment o f the growing better  film.  The  purpose  of t h i s  thesis  i s t o develop a  understanding o f the main e n g i n e e r i n g  determine  the  ultimate  performance  of  factors  the  which  unbalanced  magnetron. Two  pieces  o f experimental apparatus were designed f o r  t h i s study. A scanning magnetometer system was c o n s t r u c t e d t o measure the magnetic f i e l d allowed lines.  for a detailed A multiple,  p a t t e r n o f the magnetrons,  analysis  plasma  i n terms  probe  o f magnetic  assembly  was  which field  developed t o  measure the d i s c h a r g e c h a r a c t e r i s t i c s f o r v a r i o u s unbalanced magnetron c o n f i g u r a t i o n s . The r e s u l t s showed t h a t the i o n f l u x t o the s u b s t r a t e h i g h l y dependant  on the development  away from  the t a r g e t  generated  through  surface.  confinement  The of  was  o f a secondary d i s c h a r g e secondary d i s c h a r g e was ionizing  electrons  in a  magnetic b o t t l e a l o n g the magnetron a x i s . The i o n f l u x t o the s u b s t r a t e was observed t o be approximately independent o f the pressure  and t a r g e t  m a t e r i a l but  ii  h i g h l y dependant  on the  discharge flux  current  ratio  and t a r g e t  increased  with  thickness. decreasing  The  ion/deposition  target-to-substrate  d i s t a n c e . However, t h e u s e f u l d e p o s i t i o n area decreased under these c o n d i t i o n s  as t h e i o n c u r r e n t s  about t h e a x i s .  iii  became h i g h l y  focused  TABLE OF CONTENTS Abstract  i i  Table of Contents  iv  L i s t o f Tables  vi  L i s t of Figures  vii  Acknowledgements  ix  Chapter I. I n t r o d u c t i o n A. Magnetron S p u t t e r i n g B. T h i n F i l m M i c r o s t r u c t u r e C. Methods of Zone T T h i n F i l m P r o d u c t i o n D. H i s t o r y of Unbalanced Magnetrons E. O b j e c t i v e of T h e s i s Chapter I I . Theory A. I n t r o d u c t i o n B. Plasma Theory C. Plasma Probe Theory D. Gas Phase C o l l i s i o n s E. E l e c t r o n Motion i n a Plasma F. P l a n a r Magnetron Discharge Chapter i l l . Magnetic Measurement System A. I n t r o d u c t i o n B. Magnetic F i e l d L i n e P l o t t i n g C. Measurement System 1. Design 2. Alignment and C a l i b r a t i o n 3. Magnetic F i e l d Scan T e s t s Chapter IV. Plasma Probe A. I n t r o d u c t i o n B. Measurement System 1. Design 2. Alignment 3. Operation Chapter V. Experimental D e t a i l s A. I n t r o d u c t i o n B. R e s u l t s from V a r y i n g the S t r e n g t h Between the Annular and Centre Magnet . 1. Magnetron C o n f i g u r a t i o n s 2. Data C o l l e c t i o n and P r o c e s s i n g .. 3. Magnetic F i e l d L i n e P l o t s  iv  1 1 7 . 8 10 13 15 15 15 17 20 21 24 26 26 28 32 32 37 40 42 42 42 42 45 46 47 47 48 48 49 50  4. Plasma Probe Measurements 5. R e s u l t s with l a r g e plasma probe . 6. R e s u l t s w i t h s m a l l probes 7. D i s c u s s i o n C. Centre P i e c e Geometry and Target Thickness E f f e c t s 1. I n t r o d u c t i o n 2. Experimental r e s u l t s 3. D i s c u s s i o n D. Plasma C h a r a c t e r i s t i c s o f Unbalanced Magnetrons 1. I n t r o d u c t i o n 2. Target m a t e r i a l 3. Discharge c u r r e n t 4. Pressure E. I o n / D e p o s i t i o n F l u x R a t i o 1. I n t r o d u c t i o n 2. D e p o s i t i o n f l u x measurements .... 3. I o n / D e p o s i t i o n f l u x maximization  55 56 57 60 68 68 71 71 74 74 74 75 76 76 76 77 79  Chapter V I . C o n c l u s i o n  82  References  85  Appendix  87  v  L i s t o f Tables Table 5.1  Page  Magnetic C o n f i g u r a t i o n s  49  5.2  Discharge a t 200 mA  c h a r a c t e r i s t i c s measured by the l a r g e probe  5.3  R e s u l t s f o r the l a r g e probe f o r magnetrons 5 and 6 ...  vi  57 70  L i s t of Figures Figure  Page  1.1  P l a n a r magnetron s p u t t e r i n g system  2  1.2  Cathode assembly  3  1.3  Unbalanced magnetron  10  2.1  I-V c h a r a c t e r i s t i c s o f a plasma probe  18  2.2  P o t e n t i a l v a r i a t i o n near a n e g a t i v e e l e c t r o d e  19  3.1  C i r c u l a r magnetron  27  3.2  C r o s s - s e c t i o n o f a r e c t a n g u l a r magnetron  27  3.3  E l e c t r o n i c s of magnetic f i e l d measurement system ... 33  3.4  Mechanical aspects of magnetic f i e l d measurement system  36  4.1  Plasma probe system  43  4.2  E l e c t r i c a l components o f plasma probe  44  5.1  Magnetron 1  51  5.2  Magnetron 2  51  5.3  Magnetron 3  52  5.4  Magnetron 4  52  5.5  Magnetron 5  53  5.6  F i e l d s t r e n g t h along magnetron a x i s  54  5.7  Ground c u r r e n t s f o r magnetrons 1 t o 5  57  5.8  Ion c u r r e n t s f o r magnetrons 1 t o 5  58  5.9  R a d i a l dependence o f i o n c u r r e n t s f o r magnetron 1 .. 59  5.10  R a d i a l dependence o f i o n c u r r e n t s f o r magnetron 5 .. 59  vii  5.11  Secondary magnetic b o t t l e f i e l d l i n e  65  5.12  Magnetron 6  69  5.13  F i e l d s t r e n g t h along a x i s f o r magnetrons 5 and 6 ... 69  5.14  Ground c u r r e n t s f o r magnetrons 5 and 6  70  5.15  Ion c u r r e n t s f o r magnetrons 5 and 6  71  5.16  Ion c u r r e n t s versus d i s c h a r g e c u r r e n t  75  5.17  D e p o s i t i o n r a t e s along magnetron a x i s  78  5.18  Ion/Deposition  80  5.19  Ion c u r r e n t s versus r a d i a l p o s i t i o n  f l u x r a t i o along magnetron a x i s  viii  (normalized)  ... 80  ACKNOWLEDGEMENTS First, supervisor,  I would  like  t o give  Dr. R.R. Parsons,  my thanks  t o my  f o r a l l h i s help,  research  i d e a s , and  encouragement throughout t h e course o f my t h e s i s . I would a l s o like  t o thank  support,  a l l those  i n the l a b that  have  lent  their  i n c l u d i n g Peter Mulhern f o r h i s t i m e l y a d v i c e , and  most e s p e c i a l l y Norman Osborne f o r h i s constant  input  during  this project. I  must  also  technical staff  acknowledge t h e mechanical  and e l e c t r o n i c  i n t h e P h y s i c s department and Jack Bosma i n  p a r t i c u l a r f o r t h e i r h e l p f u l advice and a s s i s t a n c e d u r i n g t h e d e s i g n and c o n s t r u c t i o n o f t h e experimental Finally financial  I would assistance  like  t o give  o f R.R.  my a p p r e c i a t i o n  Parsons,  B r i t i s h Columbia and t h e B.C. Science  ix  apparatus. for  the  the University of  Council.  CHAPTER I.  A.  INTRODUCTION  MAGNETRON SPUTTERING Magnetron s p u t t e r i n g has  developed over the p a s t  y e a r s i n t o a predominant method f o r the films.  deposition  Though each d e p o s i t i o n technique has  magnetron s p u t t e r i n g allows  twenty of  thin  i t s advantages,  f o r a p a r t i c u l a r l y wide range of  applications. The  sputter  process  is  essentially  one  of  momentum  t r a n s f e r whereby the m a t e r i a l of i n t e r e s t f o r d e p o s i t i o n , target,  i s bombarded by  energetic  particles,  usually  or  ions.  T h i s causes the e j e c t i o n of t a r g e t atoms, a p o r t i o n of which then condense onto a s u b s t r a t e , u s u a l l y p o s i t i o n e d between 4 t o 12 cm from the t a r g e t s u r f a c e . use  chemical  almost any  and/or thermal  material  extremely v e r s a t i l e .  can  U n l i k e other methods, which  techniques  sputtered.  for dissociation,  T h i s makes the  Another major advantage o f  s p u t t e r i n g i s the ease t o which i t lends  process  magnetron  i t s e l f to  Research t h a t i s done on s m a l l , r e l a t i v e l y inexpensive  scale-up. systems  can be a p p l i e d t o the development of l a r g e , i n d u s t r i a l ones. Other a t t r a c t i v e f a c t o r s i n c l u d e f i l m s u r f a c e smoothness, the ability  to  control  film  uniformity  a b i l i t y t o d e p o s i t over a l a r g e  and  thickness,  and  the  area.  A schematic of a p l a n a r magnetron system i s shown i n F i g . 1.1  and  Fig.  1.2.  a more d e t a i l e d drawing of the cathode assembly, i n There are a number of other geometries i n use, 1  such  Introduction / 2 INERT GAS  REACTIVE GAS  SUBSTRATE CATHDDE ASSEMBLY  HOLDER  SUBSTRATE  VACUUM CHAMBER  HIGH  VACUUM  PUMP  F i g u r e 1.1 Schematic o f a p l a n a r magnetron s p u t t e r i n g system. The cathode assembly i s shown i n g r e a t e r d e t a i l i n F i g . 1.2 as a c y l i n d r i c a l c o n f i g u r a t i o n , but the p l a n a r ( f l a t t a r g e t ) 1  system i s the only type c o n s i d e r e d i n t h i s t h e s i s . deposition process  the vacuum  During the  chamber i s i n i t i a l l y  down t o a p r e s s u r e o f approximately 1 x 10"  6  Torr.  An  pumped inert  gas, such as argon, i s then i n t r o d u c e d t o r a i s e the p r e s s u r e to  1 - 10 mTorr.  Often a r e a c t i v e gas such as n i t r o g e n o r  oxygen i s a l s o employed, t o produce a d i e l e c t r i c f i l m , e.g. a  Introduction  / 3  F i g u r e 1.2 Schematic o f t h e cathode assembly o f a p l a n a r magnetron system. A l s o i n c l u d e d i s t h e e l e c t r i c a l b i a s i n g . n i t r i d e o r oxide o f the t a r g e t m a t e r i a l . the d e s i r e d pressure,  A f t e r t h e gas i s a t  a negative p o t e n t i a l i s applied t o the  t a r g e t w h i l e t h e chamber and p a r t o f t h e t a r g e t assembly a r e usually  grounded,  applied voltage  which  creates  a plasma  can be e i t h e r dc o r r f .  required f o r insulating targets.  discharge.  The  The l a t t e r mode i s  P o s i t i v e ions i n t h e plasma  bombard the t a r g e t s u r f a c e , r e s u l t i n g i n t h e e j e c t i o n o f both neutral  atoms  and  secondary  electrons,  s p e c i e s such as n e g a t i v e i o n s . condenses onto t h e s u b s t r a t e An  important  factor  as  well  as  other  A p o r t i o n o f t h e e j e c t e d atoms of i n t e r e s t , producing a f i l m .  in  the  sputtering  process  is  Introduction s u s t a i n i n g the plasma d i s c h a r g e . the  l o s s of  i o n - e l e c t r o n p a i r s needs t o be  l o s s r e s u l t s from i o n - e l e c t r o n walls,  In o r d e r t o a c h i e v e  i o n n e u t r a l i z a t i o n on  through the grounded  the  target,  this,  overcome.  recombination on the and  / 4  This  chamber  electron  loss  surfaces.  The l o s s o f i o n - e l e c t r o n p a i r s can be overcome through the emission  of  bombardment initially kinetic  secondary of  the  target.  accelerated  energy  electrons  through  turn,  and/or  bombard  The  the  target  process  of  ion  electrons  are  surface  field.  gaining  They then  atoms, which o f t e n  ionization.  the  target  electric gas  the  secondary  away from the  undergo c o l l i s i o n s w i t h the excitation  during  The  surface  newly  created  producing  more  can  involve ions,  in  secondary  e l e c t r o n s , making the process s e l f - s u s t a i n i n g . The use  of  s p u t t e r i n g method was magnetic  fields . 2  p r a c t i c e ; however, i t has i t s range o f a p p l i c a t i o n s .  i n i t i a l l y developed without the This  method  is  still  used  a number of problems which The  in  limits  f i r s t of these r e s u l t s from a  t r a d e o f f between e f f i c i e n t use o f the secondary e l e c t r o n s f o r i o n i z a t i o n and  the d e p o s i t i o n r a t e .  At p r e s s u r e s low  t o prevent s i g n i f i c a n t s c a t t e r i n g of the d e p o s i t i o n mean f r e e  path  target  anode d i s t a n c e .  to  of  the  electrons As  a  can  be  comparable  r e s u l t , there  enough i o n i z a t i o n t o s u s t a i n the d i s c h a r g e .  may  enough  f l u x the to not  the be  T h i s problem can  be overcome a t h i g h e r p r e s s u r e s but at the c o s t o f a reduced deposition flux.  A second problem i s t h a t the growing f i l m i s  Introduction  / 5  s u b j e c t e d t o bombardment by h i g h l y e n e r g e t i c e l e c t r o n s w i t h an energy comparable t o the  cathode v o l t a g e ;  e.g.  500  V.  Such  bombardment o f t e n causes f i l m damage. These problems can be overcome through the a p p l i c a t i o n of a magnetic f i e l d p a r a l l e l t o the t a r g e t s u r f a c e . c o n d i t i o n s the e l e c t r o n s are s t i l l  Lorentz  force.  about a c e n t r e  The  For the p l a n a r  back towards the t a r g e t  by  e l e c t r o n s undergo c y c l o i d a l motion  which d r i f t s  both the e l e c t r i c and  these  i n i t i a l l y a c c e l e r a t e d away  from the s u r f a c e , but are f o r c e d the  Under  i n a d i r e c t i o n perpendicular  to  the magnetic f i e l d ( E x B m o t i o n ) . 3  magnetron assembly shown i n F i g 1.2,  the  source of the f i e l d c o n s i s t s of an annular and  c e n t r e magnet  mounted  As  on  a  high  permeability  pole  piece.  the  outer  magnet completely surrounds the i n n e r magnet, the d r i f t has closed  path.  This  traps  the  electrons  c l o s e t o the  s u r f a c e and i n c r e a s e s t h e i r e f f e c t i v e path l e n g t h . to  sufficient  i o n i z a t i o n to  sustain  the  target  This  discharge  a  leads  at  much  lower p r e s s u r e s than f o r non-magnetic methods. I d e a l l y a l l of the magnet f i e l d annular  magnet  should  return  to  l i n e s o r i g i n a t i n g on the  maximize the e l e c t r o n t r a p ( F i g 1.2) . practice  for  a  though i t can the  centre  planar  be  and  magnetron  approximated by  annular magnets.  centre  in  to  T h i s i s not p o s s i b l e i n  due  to  fringing effects,  e q u a l i z i n g the The  order  the  strength  of  above c o n f i g u r a t i o n  is  sometimes r e f e r r e d t o as a balanced magnetron.  However, even  under  imperfect  ideal  conditions,  the  trap  is  still  as  Introduction / 6 e l e c t r o n s can escape through energy gained electron collisions,  i n t e r a c t i o n s with  through e l e c t r o n -  the  instabilities  in  the plasma , and along the f i e l d l i n e s near the c e n t r e o f the 4  target.  This  substrate.  leads  The  to  a  problem  plasma  can  be  in  the  vicinity  of  the  overcome  by  the  partially  placement of the ground s h i e l d so as t o i n t e r s e c t the l i n e s such as t h a t ground s h i e l d  i n F i g 1.2.  field  lines.  ionization  Under these c o n d i t i o n s  the  w i l l p r o v i d e an e f f e c t i v e r e t u r n path t o ground  f o r the e l e c t r o n s due the  field  at  t o confinement of the e l e c t r o n s  This  low  results in a  pressures  and  system with  with  a  plasma  across  efficient discharge  predominately i n the v i c i n i t y of the t a r g e t . A  different  type  of  plasma  discharge  results  if  the  annular magnet i s made much s t r o n g e r and/or w i t h a l a r g e r area than the c e n t r e magnet( F i g 1.3). substrate  can  bombardment . 5  and, bias can  undergo The  significant  t o -35  a c t u a l l y be  applications. microstructure  electron  and  e l e c t r o n f l u x i s u s u a l l y of a low  t h e r e f o r e , can be r e p e l l e d by ( -10  Under these c o n d i t i o n s  V)  applying a small  t o the s u b s t r a t e .  advantageous  i f not  T h i s i s b e s t understood  The  the ion  energy negative  i o n bombardment  crucial  for  certain  by f i r s t examining the  of t h i n f i l m s t h a t r e s u l t s under a number of  different deposition conditions.  Introduction / 7 B. THIN FILM MICROSTRUCTURE F i l m s t h a t are d e p o s i t e d under c o n d i t i o n s where t h e growth temperature i s l e s s than about 30% o f t h e m e l t i n g p o i n t o f t h e deposited  material  microstructure .  have  what  i s referred  A t these temperatures  6  t o as a  the f i l m  zone 1  initially  grows around p r e f e r r e d n u c l e a t i o n s i t e s  l o c a t e d a t areas o f  s u b s t r a t e inhomogeneties and roughness.  Atoms r e a c h i n g these  sites  will  i n i t i a l l y be l o o s e l y bounded t o t h e f i l m  lattice  and a r e r e f e r r e d t o as adatoms. The m o b i l i t y o f t h e adatoms i s low  under  zone  1 conditions  and they w i l l  t r a v e l between t h e n u c l e a t i o n s i t e s .  not be a b l e t o  As t h e n u c l e a t i o n s i t e s  grow i n s i z e they w i l l prevent f u r t h e r d e p o s i t i n g atoms from r e a c h i n g t h e s u b s t r a t e through shadowing e f f e c t s . microstructure  Hence t h e  i s c h a r a c t e r i s e d by long columns separated by  s i g n i f i c a n t voids.  The r e s u l t i n g  film  has a l a r g e  surface  roughness and p r o p e r t i e s t h a t a r e q u i t e u n l i k e t h a t o f t h e b u l k m a t e r i a l and i s o f t e n u n s u i t a b l e f o r many a p p l i c a t i o n s . Different  microstructures  temperatures. melting point  a t higher  F o r temperatures between  deposition  30 and 50% o f t h e  p o i n t t h e m o b i l i t y o f t h e adatoms i n c r e a s e s  where they  can undergo  g r a i n boundaries.  i s r e f e r r e d t o as zone 2. the r e s u l t  significant  The f i l m m i c r o s t r u c t u r e  columnar g r a i n s separated  50%,  result  diffusion  t o the on t h e  then c o n s i s t s o f  by i n t e r c r y s t a l l i n e boundaries and F o r s u b s t r a t e temperatures above  i s a zone 3 m i c r o s t r u c t u r e  where  diffusion  w i t h i n t h e g r a i n s leads t o a f i l m c h a r a c t e r i z e d by equiaxed  Introduction / 8 grains. Though zones 2 and 3 number o f t h i n f i l m  have d e s i r a b l e p r o p e r t i e s  applications, the deposition  fora  conditions  r e q u i r e d o f t e n makes t h i s method o f f i l m growth i m p r a c t i c a l , especially that  i f the substrate  of the f i l m  has a m e l t i n g  o r can be damaged  Fortunately  high  quality  temperatures  (e.g.  80°C) i f t h e  particle  bombardment  films  during  point  at high  can  be  lower than  temperatures. grown  substrate  at  low  i s subjected t o  the deposition  process.  The  bombarding p a r t i c l e s , e i t h e r ions o r e n e r g e t i c n e u t r a l s , w i l l both  impart  energy  into  t h e growing  film,  increasing the  adatom m o b i l i t y , and forward s p u t t e r t h e f i l m m a t e r i a l . above  processes  result  i n a microstructure  densely packed f i b r o u s g r a i n s . zone T, have smooth s u r f a c e s ,  The  consisting of  These f i l m s , r e f e r r e d t o as h i g h d e n s i t i e s and p r o p e r t i e s  close t o that of the bulk values.  Examples o f a p p l i c a t i o n s  for  resistant  zone  coatings  7  T  films  include  wear  metallurgical  , and diamondlike t h i n f i l m s . 8  C. METHODS OF ZONE T THIN FILM PRODUCTION There a r e a number o f methods c u r r e n t l y i n use f o r t h e deposition alternative source  9  o f zone  sputtering  t o provide  discharge.  T  thin  films.  One  o f these  i s an  technique which uses a s e p a r a t e i o n  target  bombardment  instead  o f a plasma  There a r e two main v a r i a t i o n s o f t h e above method  which a l s o p r o v i d e bombardment o f t h e s u b s t r a t e .  The f i r s t i s  Introduction / 9 t o simply supply another i o n source, t h i s time d i r e c t e d a t the substrate.  The  second  source  should  supply  p a r t i c l e s at  a  lower energy than the f i r s t i n order t o prevent r e s p u t t e r i n g of the d e p o s i t e d f i l m . so  that  the  bombard the  ions  Another method p o s i t i o n s the  directed  substrate,  towards  the  target  though a t a more o b l i q u e  substrate will  also  angle.  The  disadvantage o f growing zone T f i l m s i n t h i s manner i s t h a t ion beam s p u t t e r i n g does not l e n d i t s e l f as e a s i l y t o s c a l e up as t h a t o f magnetron s p u t t e r i n g . Ion  bombardment  can  also  be  achieved  in  conventional  magnetron s p u t t e r i n g as incomplete t r a p p i n g of the electrons  results  substrate.  in  a  plasma  in  the  proximity  energy o f the bombarding ions can  b i a s i n g of the s u b s t r a t e . is  that  the  of  the  The plasma can be f u r t h e r enhanced by a l t e r i n g the  ground s h i e l d so t h a t i t does not i n t e r s e c t the The  secondary  ion  flux,  be  field  lines.  c o n t r o l l e d through  The main problem w i t h t h i s method  typically  between  5  to  10%  of  the  d e p o s i t i o n f l u x , i s o f t e n too low t o produce the d e s i r e d f i l m 1 0  properties. The  magnetron  a l t e r n a t i v e t o the ease o f d e s i g n ratio  and  system  of  Fig.  systems d e s c r i b e d s c a l e up  and  ( t y p i c a l l y between 2 t o  10  1.3  is  above.  a high  an  attractive  I t o f f e r s both  ion/deposition  f o r metal t a r g e t s ) .  This  system, o f t e n r e f e r r e d t o as an unbalanced magnetron, has p o t e n t i a l t o make magnetron s p u t t e r i n g even more wide than i t p r e s e n t l y i s .  flux  the  ranging  A summary of the s t a t e o f the a r t f o r  I n t r o d u c t i o n / 10  Figure 1.3 Schematic o f a cathode assembly w i t h an unbalanced magnetron. Here t h e ground s h i e l d has been c u t back so t h a t t h e f i r s t s u r f a c e t h a t i n t e r s e c t s t h e f i e l d l i n e s i s the substrate.  the unbalanced magnetron i s d i s c u s s e d  i n t h e next s e c t i o n .  D. HISTORY OF UNBALANCED MAGNETRONS There  had  been  very  little  research  done  on  the  c o r r e l a t i o n between the magnetic f i e l d c o n f i g u r a t i o n and t h e ion bombardment o f t h e s u b s t r a t e i n magnetron s p u t t e r i n g p r i o r t o 1986.  I t had been confirmed, as mentioned p r e v i o u s l y , t h a t  the i o n f l u x was t y p i c a l l y 5%-10% o f t h e d e p o s i t i o n f l u x f o r most dc magnetrons.  There had a l s o been some i n v e s t i g a t i o n s  on t h e e f f e c t s o f i o n bombardment o f t h e  substrate  through  I n t r o d u c t i o n / 11 the  use  sources the  11,12  of  external  .  For dc magnetrons the o n l y major work i n v o l v e d  a p p l i c a t i o n of  magnetic  a  magnet  i n c r e a s e d i o n f l u x was as t o a i d the f i e l d The  fields  behind  with  the  rf  magnetron  substrate .  An  13  observed i f the magnet was  placed  so  of the annular magnet.  f i r s t papers  to deal s p e c i f i c a l l y with  5,14  magnetrons were p u b l i s h e d i n 1986.  unbalanced  The papers made r e f e r e n c e  t o two types o f unbalanced magnetrons, one where the magnetic f l u x from the c e n t r e magnet was much g r e a t e r than t h a t f o r the annular first  magnet and  the  s u p p l i e d very  low  further i n this text. f l u x a t the  second  f o r the  i o n f l u x e s and  opposite will  case.  not  The  considered  The second p r o v i d e d a c o n s i d e r a b l e i o n  substrate.  The magnetron d i s c h a r g e had been analyzed by the use o f a l a r g e probe , 10 cm  i n diameter, l o c a t e d along the magnetron  5  axis.  In a d d i t i o n i t had  along  a  radius  information.  of  the  a number of s m a l l e r probes p l a c e d larger  one  to  provide  spatial  For a magnetron and ground s h i e l d c o n f i g u r a t i o n  such as t h a t i n F i g . 1.3  the l a r g e probe c o l l e c t e d a l l of the  d i s c h a r g e c u r r e n t when grounded, and  i o n c u r r e n t s as h i g h  as  10 mA/cm i n the c e n t r e when b i a s e d a t -100V. T h i s r e s u l t e d i n a i o n / d e p o s i t i o n f l u x r a t i o between 2 and 10 f o r most m e t a l l i c targets. was  F u r t h e r i n v e s t i g a t i o n s r e v e a l e d t h a t the  highly  dependant  on  the  discharge  current  independent of the gas p r e s s u r e and t a r g e t There were two  b a s i c mechanisms c i t e d  ion  and  flux  fairly  composition. to explain  these  I n t r o d u c t i o n / 12 effects. field  One  lines  was  was  that  the  When the probe was  the  first  probe,  surface  rather  than  to  the  i n t e r s e c t the ground  shield.  grounded i t would serve as the anode of the  system and c o l l e c t the d i s c h a r g e c u r r e n t .  The i o n s d r i f t  with  the e l e c t r o n s t o preserve the charge n e u t r a l i t y of the plasma. At  -100V  leaving  bias  only  the  electron  flux  i o n bombardment.  is effectively  I t was  along the magnetron a x i s t h e r e was  repelled,  a l s o noted  that  a c o n s t r i c t i o n o f the  l i n e s which c r e a t e d a magnetic m i r r o r .  T h i s was  out  field  thought t o  p r o v i d e an e l e c t r o n t r a p , l e a d i n g t o f u r t h e r i o n i z a t i o n away from  the  target  surface.  The  mechanisms  involved  in  ion  p r o d u c t i o n c o u l d not be d i s c u s s e d any f u r t h e r than t h i s due a  lack  of  magnetic  information  on  the  quantitative  aspects  of  to the  field.  Though the above-mentioned would demonstrate the p o t e n t i a l of the unbalanced magnetron, t h e r e was ion  d i s t r i b u t i o n was  axis.  a drawback i n t h a t the  h i g h l y concentrated  With the probe l o c a t e d  about the magnetron  at a distance  6 cm  from  the  t a r g e t f a c e the i o n f l u x decreased by almost a f a c t o r o f f i v e at  2 cm  along  the  radius  of the  probe.  The  distribution  became more spread out f u r t h e r along the a x i s , but along  with  an o v e r a l l r e d u c t i o n i n the i o n f l u x . There were a s e r i e s of p u b l i c a t i o n s " 1 5  1 7  which d e a l t  with  the m o d i f i c a t i o n of f i l m p r o p e r t i e s with the use o f unbalanced magnetrons. zone  1  to  Data were g i v e n a  zone  T  t o show the  microstructure  transition  with  from a  increased  ion  I n t r o d u c t i o n / 13 bombardment. The  most r e c e n t p a p e r  t o date, b e f o r e t h i s t h e s i s , a l s o  18  d e a l t w i t h the nature of the plasma d i s c h a r g e f o r unbalanced magnetrons. substrate  The  r e s u l t s showed an i n c r e a s i n g i o n f l u x t o  as the  magnetic c o n f i g u r a t i o n  unbalanced towards the  became  annular magnet.  the  increasingly  I t a l s o showed  that  the i o n f l u x became more c o n c e n t r a t e d about the magnetron a x i s under  these  further  conditions.  analysis  of  It  the  did  not,  mechanisms  however,  involved  q u a n t i t a t i v e d e t a i l s of the magnetic f i e l d  E.  offer  any  give  any  or  configuration.  OBJECTIVE OF THESIS In p r e v i o u s i n v e s t i g a t i o n s of unbalanced magnetrons,  description indicated  of  the  magnetic  i n F i g . 1.3  and  field  has  discussed  been  i n part  qualitative D.  I t would be  advantageous t o be  above c o u l d be v a l i d a t e d and  able  t o understand  aid  in  magnetrons and  the  design  i n scale  these  The arguments g i v e n  i t would be p o s s i b l e t o i d e n t i f y  o t h e r f a c t o r s t h a t might be  great  in  been p o s s i b l e .  mechanisms i n a more q u a n t i t a t i v e manner.  any  as  Therefore,  only a q u a l i t a t i v e d e s c r i p t i o n o f the mechanisms i n v o l v e d i o n p r o d u c t i o n has  the  of  involved. more  This  efficient  would be  a  unbalanced  up.  Though a complete q u a n t i t a t i v e d e s c r i p t i o n would be i d e a l , in  practice  this  is  quite  difficult  to  achieve.  Plasma  d i s c h a r g e s are d i f f i c u l t t o analyze and c o n v e n t i o n a l magnetron  I n t r o d u c t i o n / 14 sputtering despite  itself  the  i s not  lack  of  a  completely thorough  understood.  However,  understanding,  magnetron  s p u t t e r i n g has grown i n t o a wide and d i v e r s e f i e l d .  Often a  s m a l l i n c r e a s e i n understanding of the o v e r a l l p r o p e r t i e s has l e a d t o a wider range  of a p p l i c a t i o n s .  The  same should  be  take an e n g i n e e r i n g approach  to  p o s s i b l e f o r unbalanced magnetrons. T h i s t h e s i s , then, w i l l  the a n a l y s i s of unbalanced magnetrons.  The emphasis w i l l  be  on a i d i n g unbalanced magnetron d e s i g n and s c a l e up through a semi-quantitative  analysis  intended t o a i d the t h i n investigation This w i l l  of  the  include  of the phenomena.  f i l m r e s e a r c h e r through a  properties  how  Also,  of  unbalanced  t o maximize both the  i t is  thorough  magnetrons.  ion/deposition  r a t i o and the e f f e c t i v e area of s u b s t r a t e bombardment. In  order  experimental magnetic  to  accomplish  apparatus  field  and  one  were  these  goals,  designed;  t o measure the  one  two to  pieces measure  resulting  of the  discharge  characteristics. As the d i s c h a r g e i s v e r y dependant on the nature of the magnetic  field,  t h e r e was  a natural  r e s u l t s o f these two experiments.  c o u p l i n g between  the  T h e r e f o r e , when a parameter  was v a r i e d , such as the r a t i o of s t r e n g t h s of the magnetron's annular  and  c e n t r e magnet  both  experiments  b e f o r e another parameter was changed.  were  conducted  T h i s method r e s u l t e d i n  a more immediate understanding of the mechanisms i n v o l v e d and helped determine the d i r e c t i o n of the next s e t o f t e s t s .  CHAPTER II.  A.  THEORY  INTRODUCTION T h i s chapter d i s c u s s e s t h e t h e o r y o f magnetron d i s c h a r g e s .  An understanding  o f b a s i c p h y s i c s o f magnetrons i s necessary  f o r both t h e d e s i g n o f t h e measurement systems o u t l i n e d i n Chapter  1, and f o r an a n a l y s i s o f t h e observed  l a t e r chapters. Chapter only  phenomena i n  I n keeping w i t h t h e o b j e c t i v e d i s c u s s e d i n  1, t h e t h e o r y d i s c u s s e d i n t h i s c h a p t e r i s o u t l i n e d  rather  mathematical  than  being  developed  with  a  great  some  general  understanding  plasma  theory  o f t h e remainder  necessary  of the t o p i c s .  d e a l s w i t h t h e theory o f plasma probes probe designed i n t h i s t h e s i s . gas  phase c o l l i s i o n s ,  ions.  The f i r s t f o r the The  second  i n reference t o the  Next t h e r e i s a d i s c u s s i o n on  w i t h emphasis on those which produce  The f o u r t h t o p i c i s e l e c t r o n motion i n a plasma i n t h e  presence o f e l e c t r i c and magnetic f i e l d s . of  of  detail.  The t o p i c s a r e broken down i n t o f i v e s e c t i o n s . gives  deal  electron  trapping  i n magnetic  F i n a l l y t h e nature  fields  used  i n planar  magnetrons i s d i s c u s s e d .  B.  PLASMA THEORY A  plasma  neutral  i s a gas w i t h  atoms,  essentially  i o n s and e l e c t r o n s .  three  components,  The i o n i z a t i o n  can be  achieved e i t h e r by h e a t i n g or, as i s t h e case w i t h magnetron 15  Theory / 16 discharges,  through t h e a p p l i c a t i o n o f an e l e c t r i c  field.  In an i d e a l plasma, t h e i o n s and e l e c t r o n s w i l l have equal d e n s i t i e s and a Maxwellian energy d i s t r i b u t i o n .  The average  energy o f t h e e l e c t r o n s i s u s u a l l y much h i g h e r  than t h a t o f  the  can t r a n s f e r  ions  i n a magnetron plasma  as t h e f i e l d  energy t o l i g h t e r p a r t i c l e s more e f f i c i e n t l y . energies  for  19  e l e c t r o n s a r e 2-8 eV w h i l e  T y p i c a l average those  f o r ions,  around 0.03 eV. As t h e i o n s and t h e e l e c t r o n s have a v e l o c i t y d i s t r i b u t i o n t h e r e i s an impingement f l u x o f each s p e c i e s on any s u r f a c e i n the plasma. T h i s f l u x i s g i v e n by J  = -^p,  (2.1)  where n i s t h e p a r t i c l e d e n s i t y and c i s t h e p a r t i c l e mean speed.  F o r a plasma  products, equal.  with  predominately  first  ionization  t h e i o n and e l e c t r o n d e n s i t i e s a r e approximately  Therefore,  t h e impingement f l u x o f t h e e l e c t r o n s i s  g r e a t e r than t h a t o f t h e i o n s due t o t h e h i g h e r energy o f t h e electrons. Plasmas have p r o p e r t i e s s p e c i f i c a l l y due t o t h e presence of  free  charged  considering  particles.  the e f f e c t  s u r f a c e i n t h e plasma. causes a n e g a t i v e  One  of placing Initially,  i s best  a electrically  by  isolated  the greater e l e c t r o n flux  charge b u i l d up on t h e s u r f a c e .  w i l l then reduce t h e e l e c t r o n f l u x u n t i l ion f l u x .  illustrated  This bias  i t i s equal  t o the  The net c u r r e n t t o t h e s u r f a c e i s then zero and t h e  Theory / 17 s u r f a c e i s b i a s e d n e g a t i v e w i t h r e s p e c t t o t h e plasma. A p o s i t i v e l y charged r e g i o n e x i s t s i n f r o n t o f a s u r f a c e which has a n e g a t i v e region  bias with  l i m i t s the extent  penetrate  into  the  r e s p e c t t o t h e plasma .  t o which a dc e l e c t r i c  plasma.  This  3  The  length  of  field  the  will  field  is  dependant upon both the e l e c t r o n energy and d e n s i t y . A  grounded  surface  will  also  be  biased  negative  with  r e s p e c t t o the plasma, though t o a l e s s e r extent than one t h a t is isolated.  T h i s b i a s i s known as the plasma p o t e n t i a l .  Another diffusion.  property  of  plasmas  field will  result.  retard  t h e motion o f e l e c t r o n s  ions.  The  result  together.  and  of  ambipolar  This f i e l d w i l l  accelerate  i s t h a t the i o n s  and  that  both  o f the  the e l e c t r o n s  The e f f e c t s o f ambipolar d i f f u s i o n  impingement f l u x i s d i s c u s s e d  C.  that  I f t h e r e i s a net d r i f t o f the e l e c t r o n s from the  plasma an e l e c t r i c  drift  is  will  on the  i n the next s e c t i o n .  PLASMA PROBE THEORY  Fig.  2.1  shows  characteristics negative current  bias  the  ideal  f o r a plasma  current  probe.  When a  i s a p p l i e d t o the probe, o n l y  i s collected.  density-voltage  This current w i l l  large  enough  positive ionic  be p r o p o r t i o n a l t o  the i o n f l u x t h a t impinges upon the boundary o f t h e p o s i t i v e space  charge  potential.  region, As  and  the b i a s  i s c o l l e c t e d up becomes  to  l e s s negative,  the the  plasma probe  c o l l e c t s a s m a l l e l e c t r o n f l u x c o n s i s t i n g o f those e l e c t r o n s  Theory /  18  with an energy h i g h enough to  overcome  potential. and  the The  ion  fluxes  to  at  floating  the  the  potential.  probe  is  plasma  V , i t will  biased  potential,  c o l l e c t a l l of  p  the  electron  f l u x and In probes  impingement  F i g u r e 2.1 I d e a l c u r r e n t d e n s i t y voltage characteristic of a plasma probe.  s t a r t t o r e p e l most of the i o n s .  p r a c t i c e , the is  more  additional are  v  the  f  When the  -  electron  probe are equal a t V , probe  \_i  negative  behaviour  complicated  of  plasmas w i t h  than  discussed  respect  to  above.  The  f a c t o r s t h a t have t o be taken i n t o c o n s i d e r a t i o n  discussed  below  f o r three  interest to t h i s thesis.  points  on  the  j-V  curve  of  These are the i o n c u r r e n t a t -100  V  b i a s , the f l o a t i n g p o t e n t i a l , and the ground c u r r e n t . At -100  V the d e t e c t o r has a s u f f i c i e n t n e g a t i v e b i a s t o  r e p e l n e a r l y a l l of the e l e c t r o n s i n the plasma but not enough to  cause  bombarding  significant ions . 5  This w i l l  f l u x t h a t w i l l reach a described  above,  secondary  in  e l e c t r o n emission  give  from  the  a measurement of the  ion  substrate. practice  However, u n l i k e the case  this  is  several  magnitude g r e a t e r than the random i o n f l u x . is  due  to  neglected  the  ambipolar  nature  of  the  i n the arguments above. Before  The  of  discrepancy  plasma, i t was  orders  which  was  assumed t h a t  Theory / 19 the e l e c t r i c f i e l d d i d not penetrate point  f u r t h e r than t h e  where  electron equal.  t h e i o n and  d e n s i t i e s became  transition Positive Space Charge Region  known as t h e Bohm  2 0  sheath Fig  Plasna  In f a c t t h e r e i s a  quasi-neutral region  -kT./2e  Figure 2.2 P o t e n t i a l v a r i a t i o n i s shown i n near a n e g a t i v e e l e c t r o d e . The v a l u e o f zero corresponds t o t h e T h i s has the plasma p o t e n t i a l .  which  2.2.  e f f e c t o f i n c r e a s i n g the energy o f t h e i o n s a t t h e boundary o f the  p o s i t i v e space charge.  region  I f the ions  a r e assumed t o have k i n e t i c  i n the f i e l d  energies  free  much l e s s than  t h a t o f t h e e l e c t r o n s then, f o r a magnetic f i e l d f r e e plasma, the i o n c u r r e n t d e n s i t y  1 9  t o t h e probe i s (2.2)  where n  i s the e l e c t r o n density  e  i n g/cm , 3  T  e  the e l e c t r o n  temperature i n degrees K e l v i n , and m- t h e mass o f t h e i o n i n grams.  The i o n f l u x , then, i s dependant upon both the d e n s i t y  of t h e plasma and t h e e l e c t r o n temperature. At V , t h e f l o a t i n g p o t e n t i a l , t h e e l e c t r o n and i o n f l u x p  that  reach  floating  the detector  potential  using  a r e equal. 2.2  A  and  d i s t r i b u t i o n f o r the electrons g i v e s  derivation  assuming 1 9  a  o f the  Maxwellian  Theory / 20 kT. £ln|(-J0J—) \2.3/n 2e  (2.3)  -  e/  The  floating  potential  is  dependant  on  the  electron  temperature. A grounded  d e t e c t o r c o l l e c t s a l l o f the random e l e c t r o n  f l u x w i t h a energy g r e a t e r than the plasma p o t e n t i a l .  This  c u r r e n t can be s i g n i f i c a n t enough t o d i s t u r b the plasma and i n p r a c t i c e probes o p e r a t i n g i n t h i s r e g i o n a r e made as s m a l l as possible.  Assuming  that  the probe  i s small  enough not t o  d i s t u r b the plasma, the c u r r e n t d e n s i t y t o ground i s (2.4)  D. GAS  PHASE  COLLISIONS  There are a number of c o l l i s i o n s i n a d i s c h a r g e p r o c e s s . The most important o f these are those p r o d u c i n g i o n s ,  which  allows the plasma t o be both generated and s u s t a i n e d .  This  can occur when an e l e c t r o n has a k i n e t i c energy equal t o or g r e a t e r than the i o n i z a t i o n energy o f an atom. of  this  depends  ionization.  on  the  cross-section  The l i k e l i h o o d probability  For argon the i o n i z a t i o n t h r e s h o l d i s a t 15.8  and the maximum c r o s s - s e c t i o n occurs around 100  of eV  eV.  A gas phase c o l l i s i o n can a l s o cause e x c i t a t i o n .  This i s  of importance as the c r o s s - s e c t i o n s f o r e x c i t a t i o n are s i m i l a r t o those o f i o n i z a t i o n .  Regions o f i o n i z a t i o n  glow from the  Theory / 21 photons emitted from the r e l a x a t i o n o f e x c i t e d atoms and i o n s . It  is  unlikely  that  the  photons  are  recombination o f i o n s and e l e c t r o n s as t h e energy  and momentum  improbable  for a  recombination  need  be  two body  processes  conserved  collision.  occur  on  caused  by  the  requirement t h a t  make  this  highly  In p r a c t i c e  t h e chamber  most  walls  at  p r e s s u r e s employed i n magnetron s p u t t e r i n g .  E. ELECTRON MOTION IN A PLASMA T h i s s e c t i o n examines the e f f e c t s o f e l e c t r i c and magnetic f i e l d s on t h e motions o f e l e c t r o n s . electron  For s i m p l i c i t y , a s i n g l e  i s c o n s i d e r e d and t h e e f f e c t s  particles  and  collisions  of other  are ignored.  The  behaviour i s c o n s i d e r e d i n t h e next s e c t i o n .  charged  collective  The e l e c t r o n  motion i s then determined by **-°(g PxS).  (2.5)  +  at  m  In a uniform B f i e l d t h e e l e c t r o n s w i l l be u n a f f e c t e d i n the d i r e c t i o n o f t h e f i e l d and w i l l o r b i t t h e f i e l d l i n e s w i t h a radius o f  1  zg  where B i s i n Gauss,  3.37 (W ) /B 1/2  ±  and W  cm,  (2.6)  i s t h e energy  i n eV's o f t h e  e l e c t r o n motion p e r p e n d i c u l a r t o t h e f i e l d .  I f an e l e c t r i c  f i e l d perpendicular to B  x  i s a p p l i e d , then a d r i f t  velocity  r e s u l t s i n t h e d i r e c t i o n p e r p e n d i c u l a r t o both such t h a t  1  Theory / 22 v -l0 EjB  cm/sec,  8  d  where E  i s the f i e l d  ±  constant,  as  If B  i n volts/cm.  i s the case  (2.7)  for fields  i s not s p a t i a l l y  i n planar  magnetron  systems, then a number o f other d r i f t c u r r e n t s r e s u l t . are d e r i v e d  These  by c o n s i d e r i n g an e l e c t r o n t o have a v e l o c i t y  3  i n a magnetic  v- V ^ x f . ,  (2.8)  B-  (2.9)  field B  c+  (f -V)B , g  c  —»  where B  i s the f i e l d  c  e l e c t r o n , and ?  g  at the centre  of the o r b i t  of the  t h e p o s i t i o n o f the e l e c t r o n r e l a t i v e t o t h e  centre of i t s o r b i t .  Then, s u b s t i t u t i n g these equations i n t o  2.5 and assuming t h a t t h e magnitude o f t h e magnetic f i e l d i s much g r e a t e r than t h a t o f {f -V)B g  drift  currents  The  drift  order  result. c u r r e n t s a r e e a s i e s t t o v i s u a l i z e with t h e use  of magnetic f i e l d l i n e s . to the f i e l d  a number o f f i r s t  cl  Magnetic f i e l d l i n e s a r e t a n g e n t i a l  and the f l u x between t h e l i n e s  is a  constant.  One o f t h e f i r s t order e f f e c t s i s t h a t an e l e c t r o n w i l l f o l l o w the c u r v a t u r e  of the f i e l d ,  r a t h e r than c r o s s f i e l d  lines.  I f VB i s p a r a l l e l t o t h e magnetic f i e l d , then a f o r c e a c t s to  either  accelerate, motion.  retard,  i f the f i e l d  i f the f i e l d  lines  lines  a r e converging,  are diverging,  In t h e absence o f an e l e c t r i c  field  or  the e l e c t r o n the electrons  Theory / 23 conserve  t h e i r magnetic moment, n ,  such t h a t  m  VL -my /B, m  where v  Q  (2.10)  o  i s the v e l o c i t y perpendicular t o the f i e l d .  I f the  d r i f t v e l o c i t y i s ignored, and o n l y t h e o r b i t a l v e l o c i t y and the v e l o c i t y  parallel  t o the f i e l d ,  v  p  i s considered,  then  c o n s e r v a t i o n o f energy l e a d s t o E-  \m (v*  +v ) .  (2.11)  2  e  p  I f t h e magnitude o f t h e magnetic f i e l d must  the perpendicular  remains  constant,  decrease.  velocity.  the v e l o c i t y  i n c r e a s e s then so  However, parallel  i f t h e energy  to f i e l d  has t o  I f t h e i n c r e a s e i n B i s l a r g e enough, t h e p a r a l l e l  v e l o c i t y w i l l be reduced t o zero and t h e e l e c t r o n i s r e f l e c t e d back.  I f we c o n s i d e r t h e f i e l d  magnitude B  1  and B  2  a t two p o i n t s i n space w i t h  r e s p e c t i v e l y (with B  2  l e s s than  and B ) , 3  then t h e maximum energy o f an e l e c t r o n t h a t can be r e f l e c t e d from t h e m i r r o r i s E - ° °? * m  It  V  B  would appear t h a t , p r o v i d e d  .  (2.12)  the o r b i t a l  velocity i s  l a r g e enough, e l e c t r o n s o f any energy can be trapped magnetic m i r r o r .  by t h e  However, t h e r e s t r i c t i o n i s t h a t t h e v a l u e  of v must be s m a l l enough f o r t h e i n i t i a l assumptions, which Q  allowed f o r o n l y f i r s t order e f f e c t s i n a f i e l d n o t s p a t i a l l y constant, t o h o l d .  Theory / 24 F. PLANAR MAGNETRON DISCHARGES The  theory  outlined  o f planar  i n Chapter 1.  magnetron  In t h i s  discharges  has been  s e c t i o n t h e theory  w i l l be  developed i n more d e t a i l . As s t a t e d p r e v i o u s l y , i n a p l a n a r magnetron d i s c h a r g e , t h e secondary e l e c t r o n s a r e i n i t i a l l y  accelerated  away from t h e  t a r g e t s u r f a c e , but a r e f o r c e d back towards t h e t a r g e t through the Lorentz f o r c e .  Assuming a low emission energy, which i n  p r a c t i c e i s a few e l e c t r o n v o l t s , t h e f u r t h e s t d i s t a n c e an 2 1  emitted  e l e c t r o n w i l l t r a v e l from t h e t a r g e t s u r f a c e i s  d = — where V  T  2m„  f u r t h e r than t h e extent the plasma p o t e n t i a l .  (v -v ) d  i s the target  T  voltage.  I f the e l e c t r o n  o f t h e t a r g e t sheath,  V  d  pressures  for typical  travels  i s equal t o  I d e a l l y t h e e l e c t r o n s should r e t u r n t o  the t a r g e t w i t h t h e same k i n e t i c energy as t h a t upon However,  1 9  magnetron  o f approximately  1  sputtering Pa  emission.  conditions  and f i e l d  with  strengths  of  approximately 300 gauss, only about h a l f t h e e l e c t r o n s r e t u r n to the surface  due t o energy l o s s e s through c o l l i s i o n s and  i n t e r a c t i o n s w i t h plasma The centre  electrons  then  which d r i f t s  instabilities . 2 2  undergo  about t h e a x i s  e l e c t r o n s a r e l a r g e l y contained lines  are p a r a l l e l  c y c l o i d a l motion  o f t h e magnetron.  a  The  i n t h e r e g i o n where t h e f i e l d  t o the target  m i r r o r e f f e c t s ( F i g 1.2).  around  surface  due t o magnetic  Theory / 25 Of  interest  escape  i s t h e mechanisms through  t h e magnetron  conduction across charge r e g i o n due  electron-electron  allowing ions. et.  classical  theory  for  i n f r o n t o f t h e t a r g e t i n magnetron d i s c h a r g e s  t o the electrons  coefficient  The  electrons  a magnetic f i e l d p r e d i c t s a n e g a t i v e space  l i n e s than t h e i o n s . to  trap.  which  having  a lower m o b i l i t y  across  In p r a c t i c e i t i s b e l i e v e d interactions  i s much h i g h e r  than  f o r an e l e c t r o n m o b i l i t y  the  actual  the c l a s s i c a l greater  2 3  field  t h a t due diffusion  predictions  than t h a t  of the  D i f f u s i o n o f t h i s nature has been observed by Rossnagel  al.  2 4  discharge  when determining t h e r a t i o current.  between t h e d r i f t  and  CHAPTER III.  A.  MAGNETIC MEASUREMENT SYSTEM  INTRODUCTION A system was  designed and b u i l t t o measure t h e magnetic  f i e l d o f a c i r c u l a r magnetron, an example o f which i s shown i n F i g . 3.1.  As the magnetic f i e l d  direction  i s symmetric i n t h e a n g u l a r  t h e system had o n l y t o measure i n an r - z p l a n e .  The measurement system was automated as i t was  felt  that  i n t h e l o n g term t h i s would be the most e f f i c i e n t method o f data  collection.  The  state  o f the a r t o f microcomputers,  i n t e r f a c e cards, and e l e c t r o n i c s i s such t h a t i t i s r e l a t i v e l y easy t o d e s i g n a system capable o f h a n d l i n g l a r g e amounts of data and t a k i n g a c c u r a t e and r e p e a t a b l e measurements. Though the data c o l l e c t i o n was r e l a t i v e l y s t r a i g h t f o r w a r d , the p r e s e n t a t i o n o f the  data was not and had t o be c o n s i d e r e d  b e f o r e the system was designed i n any d e t a i l . in  how  field.  to graphically  represent  a two  The problem l a y  dimensional vector  From the d i s c u s s i o n o f e l e c t r o n motion i n a f i e l d i n  Chapter 2, i t would appear advantageous t o do so by the  field  lines.  Magnetic  field  line  plots  plotting  would  lend  themselves w e l l i n d i s c u s s i o n s on the e l e c t r o n motion i n the plasma d i s c h a r g e . Magnetic ways.  field  lines  F i r s t the f i e l d  each p o i n t i n space. lines i s  inversely  r e p r e s e n t the a c t u a l  field  i n two  l i n e s are t a n g e n t i a l t o the f i e l d a t  Secondly, the s p a c i n g between the f i e l d proportional to 26  the f i e l d  s t r e n g t h or,  Magnetic Measurement System / 27  F i g u r e 3.2 rectangular plane.  C r o s s - s e c t i o n o f an i n f i n i t e l y l o n g magnetron symmetric about t h e y-z  Magnetic Measurement System / 28 s t a t e d otherwise, lines.  magnetic f l u x i s a c o n s t a n t between  Therefore,  direction  plots  of  this  and the r e l a t i v e f i e l d  nature  will  field  show  both  s t r e n g t h f o r each p o i n t i n  space. As magnetic f i e l d  l i n e s cannot be measured d i r e c t l y , the  data had t o be processed i n o r d e r t o produce the f i e l d plots.  The  method o f p r o c e s s i n g  i s discussed  line  i n the next  section.  B. MAGNETIC FIELD LINE PLOTTING The purpose o f t h i s d i s c u s s i o n  i s t o show how  magnetic  f i e l d l i n e s can be d e r i v e d from Maxwell's e q u a t i o n s and how a careful the  c o n s i d e r a t i o n o f the c o o r d i n a t e system can  simplify  task. Consider M a x w e l l s 1  absence o f an e l e c t r i c  equations governing a system field Vxi?= — J,  (3.1)  V-B-O.  (3-2)  c  In  our system  i n the  the c u r r e n t  density,  medium i s one o f c o n s t a n t p e r m e a b i l i t y .  J , i s zero and  the  Eq. 3.1 can then be  w r i t t e n as VxB = 0 .  (3.3)  T h e r e f o r e , t h e magnetic f i e l d must be the g r a d i e n t o f a s c a l e r potential,  which,  i n analogy  to  electrostatic  fields,  is  Magnetic Measurement System / 29 r e f e r r e d t o as the magnetic s c a l e r p o t e n t i a l .  This leads to  S--V<|> .  (3.4)  m  As the f i e l d o f i n t e r e s t possesses symmetry i n the angular direction,  the  last  equation  Though the  problem  cylindrical  coordinates,  will  reduces  eventually  to  have  i t i s easiest  two  dimensions.  t o be  to f i r s t  solved  consider a  s i m i l a r problem i n the C a r t e s i a n system, t h a t o f a f i e l d a infinitely 3.2.  for  from  l o n g r e c t a n g u l a r magnetron such as t h a t i n F i g  Here B  - -  ,  m  Bx If  the  equipotential  B  '  --  .  m  (3.5)  dy  y  surfaces  of  the  magnetic  scaler  p o t e n t i a l a r e c o n s i d e r e d , from Eq. 3.4 i t can be seen t h a t the l i n e s p e r p e n d i c u l a r t o these w i l l of for  the magnetic any  well  field.  behaved  always be i n the d i r e c t i o n  From the Cauchy-Riemann scaler  field,  * (x,y) ,  dx  dy  '  such  m  above, t h e r e e x i s t s a conjugate f i e l d ,  relations, as  T ( x , y ) , such m  dy  that  that  dx  whose contours are p e r p e n d i c u l a r t o those o f * ( x , y ) .  7 (x,y)  is  and  m  referred  to  as  the  imaginary  r e l a t e d t o the magnetic f i e l d B  I f the change i n Y the  contours o f T , m  = -  m  dH m  ,  By '  scaler  potential  m  is  as By =  m  Bx  .  (3.7)  i s a c o n s t a n t , as i t w i l l  then from Eq. 3.7  the  flux  be between (B-fidAi  is a  Magnetic Measurement System / 30 constant. lines  Therefore  are s a t i s f i e d  magnetic  both  requirements  by  t h e contours  scaler potential.  of the  Hence contour  w i l l g i v e t h e magnetic f i e l d  lines.  Y ( x , y ) -V (x.O)  plots  field  imaginary o f T (x,y) |]1  The s o l u t i o n t o 3.7 i s  -f B (x.y')dy'.  (3.8)  y  m  m  f o r magnetic  x  Jo  or  T.U.y) -Y (0,y) a  + f*B (x'.y)  (3.9)  dx*.  y  I f we l e t x = 0 i n 3.8 and s u b s t i t u t e i n t o t h e 3.9, t h e result i s VJx.y)  =T (0,0) - | B ( 0 , y ) c i y f B (x',y)dx . y  m  /  o  /  x  +  X  (3.10)  f  y  ¥ (0,0) i s an a r b i t r a r y constant and can be s e t t o m  without  a f f e c t i n g the r e l a t i v e values o f t h e contours.  zero The  f i r s t i n t e g r a l can a l s o be s e t t o zero through a c o n s i d e r a t i o n of the symmetry about the B  x  on the y - a x i s i s  zero. VJx,y)  In examining equation  y - a x i s ( F i g 3.2) ; i . e . the v a l u e o f This s i m p l i f i e s  equation 3.10 t o  -f B (x',y)dx'.  (3.11)  X  o  y  3.11 we can see t h a t t h e i n t e g r a l  r e p r e s e n t s t h e f l u x through an area i n t h e x-z plane l o c a t e d at  y o f l e n g t h 0 t o x, normalized To  field  i n z.  i l l u s t r a t e how t h e contours  o f Y (x,y) r e p r e s e n t t h e m  l i n e s F i g 3.2 should be c o n s i d e r e d a g a i n .  magnetic f i e l d  and 7  As both t h e  a r e f u n c t i o n s o f x and y they  can be  Magnetic Measurement System / 31 r e p r e s e n t e d on the same s e t of axes, as w i l l next argument. Near the o r i g i n B  be done i n the  i s negative.  y  I n s p e c t i o n of  shows t h a t , near the o r i g i n , as x i n c r e a s e s Y (x,0)  Eq. 3.11  m  decreases, w i t h the d i s t a n c e between i t s contour l i n e s along the  x-axis  strength. and  the  inversely  proportional  to  the  magnetic  F u r t h e r along the a x i s the d i r e c t i o n of B value  T (x,0)  of  becomes  m  more  y  field  changes  positive.  The  contours w i l l then take the same v a l u e s of those f u r t h e r down the a x i s . Between the f i r s t f i e l d point  'a' and  the  origin  l i n e d i s p l a y e d on the x - a x i s a t  there  is a  fixed  amount of  T h i s f i e l d l i n e a l s o i n t e r s e c t s l i n e x' a t 'b'. the v a l u e o f 7  At  and the f l u x between the f i e l d  flux.  'b'  both  l i n e and  the  m  a x i s are the same. integral factor  i n 3.10  I f f l u x c r o s s e d the y - a x i s then the f i r s t  would have t o be  f o r the v a l u e of  7 .  However, due  m  symmetry, the magnetic f i e l d a x i s , hence the  employed as a  t o the  i s always p a r a l l e l  y - a x i s i t s e l f i s a contour  a n g u l a r l y symmetric and t h e r e i s no B In t h i s way  geometry r e s u l t s  instead of  dxdz.  i n an  t o the  y-  the system i s  component along the z-  i t i s analogous t o F i g 3.2.  different  area  However the  component  of  rdrdB  T h e r e f o r e , the i n t e g r a l t h a t r e p r e s e n t s the  f l u x through an area i n the r - 8 0 t o r , normalized Magnetic  r  system's  line.  In a c y l i n d r i c a l system such as F i g . 3.1  axis.  correction  field  plane l o c a t e d a t z of l e n g t h  in 6 is plots  can  be  produced  for  a  circular  Magnetic Measurement System / 32 VJr.z)  - jJr'B (x',z)dr'.  magnetron by f i r s t measuring B T  m  can then be determined  integration.  (3.12)  z  i n an r - z p l a n e . The v a l u e o f  z  a t each p o i n t  The contours o f 7  through numerical  can then be p l o t t e d through  m  a v a r i e t y o f commercial g r a p h i c s packages.  C. MEASUREMENT SYSTEM  1.  Design  A system was developed t h a t c o u l d measure t h e field  For a c i r c u l a r  magnetron  t h i s would map out the f i e l d i n an r - z plane, t a k i n g  advantage  of  i n a two dimensional g r i d .  magnetic  t h e a n g u l a r symmetry.  Though o n l y B  z  would have t o be  measured t o produce t h e f i e l d p l o t s , t h e system was designed to be a b l e t o measure e i t h e r component i n case measurements o f B  r  were d e s i r e d .  A b l o c k diagram  system i s shown i n F i g 3.3  of the e l e c t r o n i c  control  and a schematic o f t h e mechanical  aspect i n F i g 3.4. The l e v e l o f accuracy r e q u i r e d had t o be c o n s i d e r e d b e f o r e the  system  was designed  i n detail.  o b j e c t i v e s d i s c u s s e d i n Chapter  In keeping  with the  1, i t was d e c i d e d t h a t any  c a l c u l a t i o n s would o n l y r e q u i r e d measurements a c c u r a t e t o a few p e r c e n t . was in  For the p r o d u c t i o n o f f i e l d l i n e p l o t s , t h e data  integrated.  T h i s reduced the e f f e c t o f any random e r r o r s  t h e system though  c a r e had t o taken w i t h r e s p e c t t o any  Magnetic Measurement System / 33  Corrtrol Program  Computer  Lab Pac Interface Card  PdRTB •  PORTA  Axial Stepping Motor Controller  PORTC  r  Radial Stepping Motor Controller  Axial Stepping  Multiplexer  Radial Stepping Motor  Motor  Prog. Gain Amp,  Pre-Amp  8-Blt ABC  Hall P r o b e  Constant Voltage Source C12 Volts)  F i g u r e 3 . 3 Block Diagram of the e l e c t r o n i c s of the magnetic f i e l d measurement system. systematic The  errors.  f i r s t source o f s y s t e m a t i c e r r o r c o n s i d e r e d was the  detector i t s e l f .  I t had t o g i v e r e p e a t a b l e r e s u l t s but needed  o n l y be a c c u r a t e t o a few p e r c e n t .  T h e r e f o r e , a H a l l probe,  which was a c c u r a t e t o about +/- 1% , 25  was deemed s u f f i c i e n t .  A magnetometer was designed s p e c i f i c a l l y f o r t h i s system. There was a Lab  Pac  i n t e r f a c e card already a v a i l a b l e  l a b ; however, the commercial meters immediately found  t o be incompatible  with  the interface  i n the  on hand were card  for  magnetometer system. Though the meters gave a v o l t a g e  the  output  Magnetic Measurement System / 34 proportional than  that  t o the measured f i e l d ,  which  could  convertors. Also,  be  i t was  read  t h e i r maximum was  by  the  card's  less  8-bit  i m p o s s i b l e t o s e t the meters  e l e c t r o n i c a l l y , which l i m i t e d the dynamic range.  A-D gain  Rather than  o r d e r a new meter o r i n t e r f a c e c a r d i t was d e c i d e d t h a t from the  p o i n t o f view o f time and expense t h a t i t would be b e s t t o  take advantage o f the i n e x p e n s i v e H a l l probe c h i p s t h a t have recently simple  become a v a i l a b l e .  t o use  allowing f o r  and  an  These  amplifier  chips  was  t u r n e d out  custom  built  to  be  f o r them  a good d e a l o f f l e x i b i l i t y when i n t e r f a c i n g the  system w i t h o t h e r components. The H a l l probe chosen was a Sprague UGN-3501K. output  was  both  temperature  ( 1 % / l v o l t ) dependant.  and  input  voltage  The i n p u t v o l t a g e dependence was  remedied  with  a  volts.  The  temperature  operating  ( l % / 5 deg)  The probes  constant voltage  i n a controlled  source  sensitivity  easily  accurate to  was  dealt  with  0.03 by  environment where the temperature  did  not v a r y by more than 2 degrees C e l s i u s .  the  c h i p was a l s o n o n - l i n e a r f o r a p p l i e d f i e l d s o f more than  1000 Gauss. the  output  meter's  The output o f  The n o n - l i n e a r i t y was c o r r e c t e d f o r by comparing of  the  Sprague  probe  to  that  of  i n the presence o f a magnetic f i e l d .  a The  commercial field  was  s u p p l i e d by a l a r g e Helmholtz c o i l , which produces a u n i f o r m field  i n the v i c i n i t y  of i t s a x i s .  The outputs o f the  two  d e t e c t o r s were compared f o r a range o f v a l u e s between 0 and 3000 Gauss.  The  subsequent v a l u e s measured by t h e  Sprague  Magnetic Measurement System / 35 probe  could  fitting.  then  be  corrected  for  increased  the  Though t h i s  through digital  cubic  spline  e r r o r , at  maximum f i e l d measured (2400 Gauss) the n o n - l i n e a r i t y was 25%.  the only  A l s o the v a s t m a j o r i t y of data p o i n t s were below  1000  Gauss. The  output  of  the  Hall  probe  was  passed  through  a  p r e a m p l i f i e r , which had an a d j u s t a b l e g a i n and o f f s e t c o n t r o l . The  signal  level  was  increased  with  the  use  of  an  i n s t r u m e n t a t i o n a m p l i f i e r with a programable g a i n of 1, 3, and  30.  The  output  of the  a m p l i f i e r was  sent  t o an  8 bit  analog t o d i g i t a l c o n v e r t e r i n t e r f a c e d w i t h the computer. measurement system had and  an  accuracy  10  The  a dynamic range from 1 t o 3000 Gauss  between  1 to  3%  , depending  on  the  input  s i g n a l l e v e l and the a m p l i f i e r g a i n . The ports  a n a l o g - t o - d i g i t a l convertor were s u p p l i e d by a Lab Pac  and  three  i n t e r f a c e c a r d which c o u l d  be programmed w i t h a h i g h l e v e l language. set  as output p o r t s  8 b i t control  P o r t s A and B were  t o program the s t e p p i n g motor c o n t r o l l e r s  w h i l e P o r t C had f o u r i n p u t and f o u r output l i n e s f o r c o n t r o l . Two  of the output  gain while  the  l i n e s were used t o c o n t r o l remainder,  p r o v i d e d the "handshaking" which were b u i l t by the UBC The two  mechanical  perpendicular  combined  with  the  the a m p l i f i e r input  lines,  f o r the stepper motor c o n t r o l l e r s , P h y s i c s e l e c t r o n i c s shop.  system allowed directions.  f o r motion i n a plane The  stepping  motors  attached t o a d r i v i n g s h a f t of 20 threads per i n c h  in  were  and had  a  Magnetic Measurement System / 36  Lower  Guide  Bar,  Stepping  Motors  Magnetron Holder  Detector, Holder  Teflon  1 7^  Guide  U p p e r Guide Bar  F i g u r e 3 . 4 Schematic measurement system.  Driving  o f the mechanical  r e s o l u t i o n o f 200 s t e p s p e r r e v o l u t i o n .  Shafts  aspects of the  Theoretically,  made t h e p o s i t i o n accuracy b e t t e r than +/- .01 mm.  this  There was,  however, a s l i g h t wobble i n t h e system which r e s t r i c t e d t h e accuracy t o approximately +/- .05 mm.  The d r i v i n g s h a f t moved  a t e f l o n guide which rode a l o n g two p a r a l l e l b a r s .  Only one  end o f t h e u n d e r s i d e o f the t e f l o n guide had a grove i n which a  b a r would  fit,  while  the other  Therefore only the bar that  side  was  milled  flat.  f i t i n t o t h e groove had t o be  accurately aligned. The  software o f t h e system was w r i t t e n as a l i b r a r y o f  r o u t i n e s run by a main c o n t r o l l e r program. a  single  specified  function number  "handshaking".  such of  as  steps  advance or  Each r o u t i n e d i d  the stepping  performed  part  motor  a  of  the  These c o u l d then be l i n k e d t o g e t h e r by  the  main program t o run a scan o f t h e d e s i r e d c h o i c e .  Magnetic Measurement System / 37 2.  Alignment and  Calibration  The e r r o r i n the measurement of the about  1 %.  T h i s was  used  f i e l d was,  at best,  as a guide when c o n s i d e r i n g  how  p r e c i s e l y the system needed t o be c a l i b r a t e d and a l i g n e d .  It  was  be  a l s o kept i n mind t h a t the s y s t e m a t i c e r r o r s had  to  kept s m a l l enough not t o n o t i c e a b l y a f f e c t the contour p l o t s of  Y  •  m  m  The f i r s t problem t o be d e a l t w i t h was t o ensure t h a t the two t e f l o n guides ran p e r p e n d i c u l a r t o one another. was  simplified  with  only  one  of  the  two  The t a s k  s u p p o r t i n g rods  a c t i n g as a guide bar. Both t e f l o n guides were m i l l e d as r e c t a n g u l a r b l o c k s t o w i t h i n the s m a l l e s t p o s s i b l e t o l e r a n c e ( +/-  .002  " ).  The  g u i d i n g groves were then c u t p a r a l l e l t o t h e i r a d j a c e n t edge. The top g u i d i n g bar was mounted i n t o the top assembly  so t h a t  i t would l i e p a r a l l e l t o the edge, which, i n t u r n was l i n e d up w i t h edge of the lower t e f l o n guide t h a t was p e r p e n d i c u l a r t o its  groove.  It  was  found  p e r p e n d i c u l a r t o w i t h i n a 0.5  that  the  two  guides  were  of a degree.  The next step was t o a l i g n the H a l l probe d e t e c t o r so t h a t i t s a x i s was  p a r a l l e l t o the upper guide bar.  accomplished  by  s u p p l y i n g a magnetic  lower  guide bar then  until  i t s output  generate  a  field  was of  adjusting zero. 50  A  Gauss.  field  parallel  the angle Helmholtz One  T h i s c o u l d be  of the d e t e c t o r  coil  end  t o the  of  was a  used  to  straight  r e c t a n g u l a r bar was p l a c e d along the s i d e of the two c o i l s and  Magnetic Measurement System / 38 the o t h e r end l i n e d p a r a l l e l with t h e lower guide b a r . The angle o f t h e d e t e c t o r was then a d j u s t e d u n t i l i t s output +/-  .5 Gauss.  degrees. level,  This aligned the detector  t o w i t h i n +/-  As t h e e a r t h ' s magnetic f i e l d was a f a c t o r  the current  t o the c o i l  was  was  turned  .5  at this  o f f and t h e  a m p l i f i e r o f f s e t adjusted, then t h e c u r r e n t turned back on and the process repeated u n t i l t h e d e t e c t o r gave t h e same r e a d i n g i n both The  cases. detector  detector  was  preamplifier, amplifier,  was  then  calibrated.  set parallel to  unity  to  gain;  t o a maximum  gain  The  t h e Helmholtz and  the  of t h i r t y .  i n c r e a s e d i n 2.5 Gauss steps up t o 60 Gauss. fit  was performed t o determine t h e output  ratio  o f t h e system.  axis  o f the  field;  the  instrumentation The  field  was  A l e a s t squares voltage  The p r e a m p l i f i e r v o l t a g e  to f i e l d was  then  a d j u s t e d so t h a t the output l e v e l o f the a m p l i f i e r f o r 1 Gauss at  maximum g a i n was equal  t o the minimum v o l t a g e d i f f e r e n c e  t h a t t h e AD c o n v e r t o r s c o u l d d e t e c t , 39.4 mV. The f i e l d would subsequently allowed The  be measured t o w i t h i n  f o r e f f i c i e n t data  an i n t e g e r v a l u e ,  storage.  magnetron h o l d e r was then a d j u s t e d  so t h a t i t s a x i s  was a l i g n e d p a r a l l e l t o t h e a x i s o f t h e d e t e c t o r . was  This task  s i m p l i f i e d by i n i t i a l l y s e t t i n g the f a c e o f t h e magnetron  h o l d e r p a r a l l e l t o t h e upper guide bar. one  which  end o f a square was p l a c e d  To accomplish  this,  a g a i n s t t h e upper guide b a r  w h i l e t h e other end was p o s i t i o n e d approximately  1 cm from t h e  Magnetic Measurement System / 39 magnetron h o l d e r .  Then, by t h e use o f a p a i r o f c a l l i p e r s and  p l a c i n g t h e square t o e i t h e r s i d e o f t h e magnetron h o l d e r t h e f a c e was a l i g n e d .  The magnetron h o l d e r was then r o t a t e d  90  degrees a l i g n i n g i t s a x i s p a r a l l e l t o t h a t o f t h e d e t e c t o r . The h e i g h t o f the magnetron was s e t so t h a t i t s a x i s was a t t h e same l e v e l  as t h a t o f t h e d e t e c t o r .  piece with a small l a t h e , then holder. level  indent  i n i t s centre  A  cylindrical  was machined on a  p l a c e d i n t h e c e n t r e o f a magnetron s e t i n the  A l i n e on t h e d e t e c t o r h o l d e r was  as t h e c e n t r e  of the detector.  etched a t t h e same A small  square  was  p l a c e d up a g a i n s t the end o f the s t e e l p i e c e and a machined b l o c k was used t o s e t i t s h e i g h t t o t h a t o f t h e e t c h i n t h e detector  holder.  The h e i g h t  o f t h e magnetron  was  then  a d j u s t e d so t h a t the indent would be a t t h e same h e i g h t as t h e top o f t h e s t r a i g h t edge. Once t h e magnetron h o l d e r was a t t h e c o r r e c t angle and h e i g h t , t h e i n i t i a l s t a r t i n g p o s i t i o n o f the d e t e c t o r c o u l d be determined.  The s t e e l c e n t r e p i e c e was l e f t i n p l a c e from the  h e i g h t alignment.  A square was p l a c e d a g a i n s t t h a t s i d e o f  the p i e c e which was away from the main assembly.  The d e t e c t o r  was p o s i t i o n e d u n t i l the edge o f i t s h o l d e r came i n c o n t a c t with the side of the the  detector  piece  centre  diameter  square.  from t h e h o l d e r • s edge and t h e c e n t r e  the detector  T h i s was checked through which should  By measuring t h e d i s t a n c e o f  could  a scan  be p o s i t i o n e d  across  radially.  t h e magnetron  be symmetric about the o r i g i n .  face  To r e c o r d t h e  Magnetic Measurement System / 40 proper p o s i t i o n , the d i s t a n c e between the lower t e f l o n  guide  and the assembly edge along the guide bar was measured.  This  was  used t o r e z e r o the d e t e c t o r . For p o s i t i o n i n g along the a x i s a mark 3 mm  of  a  square  against  was  the  positioned  made.  face so  of  that  The the  the  end  of  centre mark  the  square  piece  bisected  from the edge  and the  was  the  placed assembly  depth  of  the  detector.  3.  F i e l d Scan T e s t s The system was i n i t i a l l y designed without the use of s h a f t  encoders  i n o r d e r t o simply the e l e c t r o n i c s and the assembly.  Scanning  t e s t s were then employed t o see i f the system would  run  with  the  desired  level  of  accuracy  without  direct  p o s i t i o n measurement. Backlash was a problem t h a t had t o be c o r r e c t e d . To a v o i d t h i s the data were always c o l l e c t e d i n the same d i r e c t i o n of motion, w i t h the d e t e c t o r moving away from the magnetron. a scan the assembly would c o l l e c t measurements i n the direction, direction, set  then  move  required  radial  r e t u r n t o the magnetron f a c e , then b e g i n  another  T h i s l e t the  l e a s t l o a d do the most of the work.  step  in  axial  the  of measurements.  the  In  s t e p p e r motor w i t h  the  In order t o e l i m i n a t e the  b a c k l a s h b e f o r e b e g i n n i n g the next s e t o f measurements i n the axial  direction,  the  detector  would  move  towards the magnetron f a c e then back a g a i n .  an  I t was  extra  step  found t h a t  Magnetic Measurement System / 41 by moving the d e t e c t o r i n t h i s manner t h a t 10 scans a l o n g the a x i s a t the same r a d i a l p o s i t i o n produced  the same r e s u l t s .  The p o s i t i o n accuracy was a l s o t e s t e d by d o i n g a scan of 65 by 65 mm final  and  measuring  p o s i t i o n was  There was  initial  and  final  a c c u r a t e t o w i t h i n +/-  a s m a l l amount o f d r i f t  I f the system was the d r i f t was  the  positions.  0.1  The  mm.  i n the v o l t a g e output.  l e f t on f o r a day b e f o r e b e g i n n i n g a scan  l e s s than 1 Gauss per day.  f i e l d l i n e p l o t took about 10 hours.  A scan t o produce a  CHAPTER IV.  PLASMA PROBE  A . INTRODUCTION A plasma probe was  designed and b u i l t t o o p e r a t e a t the  t h r e e p o i n t s on the j-V curve d i s c u s s e d  i n Chapter 2.  The  r e s u l t s would be coupled w i t h the magnetic f i e l d  information  t o h e l p understand the p r o p e r t i e s o f unbalanced  magnetrons.  The most complete study o f t h i s nature t o date was Window e t . a l . .  In  5  results  a  similar  order t o be a b l e compare w i t h  probe  was  built.  The  probe  was  done by their not  a  c o n v e n t i o n a l one i n t h a t i t was q u i t e l a r g e , and would a f f e c t the plasma d i s c h a r g e .  However, the probe was designed t o take  the p l a c e o f the s u b s t r a t e and i t s h o l d e r and hence became p a r t o f the d i s c h a r g e system. predominately  The purpose o f the probe  t o measure the e f f e c t s  o f the plasma  s u b s t r a t e , such as through i o n bombardment. still  on  was the  However, i t was  p o s s i b l e t o analyze the plasma t o a c e r t a i n e x t e n t a t  the more n e g a t i v e v a l u e s as has been done i n o t h e r s t u d i e s . 2 6  B. MEASUREMENT SYSTEM  1. Design As s t a t e d i n the I n t r o d u c t i o n , the probe was t h a t i n Ref. 5.  s i m i l a r to  A 10 cm diameter copper d i s k was  used as a  probe f o r the average behaviour o f the d i s c h a r g e w h i l e f i v e smaller  probes  of  0.8  cm 42  diameter  provided  spatial  Plasma Probe / 43  CATHODE ASSEMBLY  DRIVING ROD  DETECTOR  GUIDING RDD  '— BACKING PLATE H n  y  LEVELING SCREWS  a  RADIAL ADJUSTMENT  - FEEDTHROUGH CLAMPING BOLT  CHAMBER DDDR STEPPING MDTDR F i g u r e 4 . 1 Plasma Probe System  information.  The f i r s t o f t h e s m a l l e r probes was p o s i t i o n e d  i n t h e c e n t r e o f the l a r g e probe with t h e o t h e r s p l a c e d a t  1  cm i n t e r v a l s along a r a d i u s . Though t h e probe was very s i m i l a r t o t h a t o f Ref 5, t h e supporting adapted t o  mechanism different  ( F i g 4.1)  differed  as  s p u t t e r i n g chamber.  i t had t o be In Ref. 5  the  probe was attached t o s l i d i n g s e a l , p o s i t i o n e d d i r e c t l y under the magnetron.  Instead,  o f a r o t a r y feedthrough  i n our system, advantage which normally  turned  t a b l e by means o f a s t e p p i n g motor o u t s i d e  was taken  a substrate  o f t h e chamber.  The probe assembly c o u l d be moved along t h e magnetron's a x i s by  means  of  a  threaded  driving  rod  attached  t o the  Plasma Probe / 44  ® ± - -100 V  F i g u r e 4.2 Schematic o f e l e c t r i c a l plasma probe  components  o f the  feedthrough, w h i l e a guide rod would p r o v i d e d the n e c e s s a r y counter t o r q u e t o a l l o w only.  A  circular  feedthrough  f o r motion  indent  allowed  i n the  for a  simple  i n the a x i a l  chamber  door  direction around  clamping system  the  f o r the  guiding rod. An  assembly  support, insulating  the  probes  the  were  detector  mounted  on  was a  designed. 5  backing p l a t e which, i n t u r n , was  copper h o l d e r . in  to hold  mm  deep  For nylon  fastened into a  The d e t e c t o r h o l d e r was mounted onto a s l i d e  the main assembly  through t h r e e  levelling  screws  which  would a l l o w the probe t o be a l i g n e d p a r a l l e l t o the magnetron face.  The s l i d e i t s e l f c o u l d move along the assembly frame,  which allowed the probe t o be p o s i t i o n e d r a d i u s . The angular p o s i t i o n  along t h e chamber  of the probe c o u l d be a d j u s t e d by  Plasma Probe / 45 the placement o f the base p l a t e s . Due  to  the  electrically  insulating  isolated  backing  plate,  the  probes  were  from the chamber. A schematic o f the  e l e c t r i c a l setup i s F i g 4.2. I t should be noted t h a t d u r i n g a measurement a l l o f the probes were a t the same p o t e n t i a l .  2. Alignment The f i r s t step i n the alignment process was t o ensure t h a t the  large  presented  probe  was  parallel  some d i f f i c u l t y  to  i n that  mounted onto the chamber door.  the  target  the  probe  face.  This  assembly  was  However, as t h e door i n t h e  c l o s e d p o s i t i o n was p a r a l l e l t o the t a r g e t f a c e , the probe was aligned  t o the chamber door i n s t e a d .  During the alignment  process,  the door was  as p o s s i b l e t o a v o i d  any  problems  h e l d as v e r t i c a l  resulting  from the s h i f t i n g  o f the c e n t r e  of  gravity. Next,  the  centre  magnetron a x i s . cylindrical ground piece  the  T h i s was  piece  shield. i n which  of  that  was  aligned  done q u i t e simply  f i t snugly  A hole a felt  probe  was  the  by machining a  i n t o the opening o f the  drilled  marker  along  would  i n the c e n t r e just  fit.  The  o f the probe  p o s i t i o n c o u l d be a d j u s t e d r a d i a l l y by the s l i d e on which the detector entire  holder  assembly.  was  mounted Then  by  and  angularly  by  r o t a t i n g the  c l o s i n g t h e magnetron  door  and  o b s e r v i n g the r e s u l t i n g mark on the d e t e c t o r f a c e i t c o u l d be  Plasma Probe / 46 c e n t r e d t o w i t h i n +/were taken  .5 mm  f o r comparison  accuracy. purposes,  When the  a set of t e s t s  assembly  was  left  a l i g n e d i n the chamber f o r the e n t i r e s e t of t e s t s .  3. O p e r a t i o n Initially  the system  ran w i t h an a c c e p t a b l e  wobble i n  both the a x i a l and r a d i a l d i r e c t i o n s of approximately +/mm. of  .25  However, a f t e r a few s p u t t e r i n g runs, some of the t h r e a d the main assembly wore away and  developed.  T h i s was  an  unacceptable  wobble  c o r r e c t e d by the use o f a rubber  band  between the main assembly and the base p l a t e . A f t e r t h i s the system ran as smoothly  as b e f o r e .  CHAPTER V.  A.  EXPERIMENTAL RESULTS  INTRODUCTION The  systems d e s c r i b e d  measure  the  magnetic  i n Chapters 3 and  field  and  the  resulting  c h a r a c t e r i s t i c s f o r a s e r i e s of magnetrons. presented  in  this  Chapter  along  4 were used  with  an  The  to  discharge  r e s u l t s are  analysis  of  the  observed phenomena. The  t e s t s were broken down i n t o f o u r s e c t i o n s .  The  first  s e t of experiments i n v o l v e d examining the e f f e c t s of a l t e r i n g the r e l a t i v e s t r e n g t h s  of the c e n t r e  and  annular magnets.  For the second s e t of experiments, the e f f e c t s o f  target  t h i c k n e s s and the magnetic f i e l d c o n f i g u r a t i o n were examined. The  magnetic f i e l d was  geometry o f the c e n t r e In  the  third  configuration  was  were v a r i e d .  The  s t e e l centre. function target The ratio.  of  The  set  f u r t h e r a l t e r e d through changing  the  piece. of  experiments,  used w h i l e v a r i o u s magnetron had  an  optimum  sputtering  magnetron parameters  an annular magnet and  a mild  charged p a r t i c l e f l u x e s were measured as a  sputtering  gas  pressure,  discharge  power,  and  composition. final The  s e t of t e s t s examined the  d e p o s i t i o n r a t e s and  as a f u n c t i o n of a x i a l p o s i t i o n .  47  ion/deposition  flux  i o n c u r r e n t were determined  Experimental  B.  RESULTS FROM VARYING ANNULAR AND  THE  Results /  48  BETWEEN  THE  RELATIVE STRENGTHS  CENTRE MAGNET  1. M a g n e t r o n C o n f i g u r a t i o n s  F i v e d i f f e r e n t magnetic c o n f i g u r a t i o n s were examined i n t h i s s e t of t e s t s .  The b a s i c geometry i s shown i n F i g  In a l l cases the annular magnets were neodymium based w i t h an outer diameter of 4.95 configurations  had  a  cm and were 0.64  cylindrical  centre  neodymium a l l o y magnet or m i l d s t e e l .  The  alloy  cm deep.  piece  of  3.1.  The  either  dimensions of the  c e n t r e p i e c e were the same f o r each magnetron w i t h a r a d i u s and depth of 0.64 The  cm.  d i f f e r e n c e between  shown i n Table 5.1. was  The  the  magnetic  configurations i s  f i e l d s t r e n g t h of the c e n t r e magnet  measured on the a x i s a t a d i s t a n c e 3 mm  from the s u r f a c e .  The c e n t r e magnet of the f i r s t magnetron was w h i l e those f o r magnetrons 2 and heating,  t o 50%  strengths greatest  of value  and  the at  25%  3 were demagnetized through  of t h e i r maximum v a l u e .  annular  magnet  a distance  component measured was  f u l l y magnetized  B. z  3 mm  were from  measured the  The  field  for  their  surface.  The  The magnets were both mounted on  a m i l d s t e e l p o l e p i e c e d u r i n g the measurement p r o c e s s .  The  f l u x from the s u r f a c e of the magnets were a l s o c a l c u l a t e d f o r purpose of comparison. in  the  Appendix.  The method of c a l c u l a t i o n i s d i s c u s s e d  The r a t i o of the f l u x c r o s s i n g the s u r f a c e  Experimental Table  5.1  Magnetic  Configurations  Centre P i e c e Magnetic Config.  R e s u l t s / 49  Material  Annular Magnet  Field Strength  Inner radius  Field Strength  (Gauss)  (cm)  (Gauss)  1  Neo. A l l o y  2300  2.05  950  2  Neo. A l l o y  1800  2.05  930  3  Neo. A l l o y  1350  2.05  910  4  Mild  Steel  700  2.05  900  5  Mild  Steel  1450  1.65  1500  (when i s o l a t e d ) between the annular magnet and c e n t r e magnet f o r c o n f i g u r a t i o n 1 i s , t o w i t h i n a few p e r c e n t , 2. of  t h e f l u x between t h e  is  1.5.  2. D a t a C o l l e c t i o n  All  annular magnets o f magnets 5  and 1  and P r o c e s s i n g  o f t h e magnetic f i e l d  the same procedure.  The r a t i o  measurements were taken  A g r i d o f data p o i n t s spaced  1 mm  with apart  i n t h e a x i a l d i r e c t i o n and 0.5 mm r a d i a l l y was c o l l e c t e d f o r the v a l u e o f B . z  The g r i d extended 6.4 cm along t h e a x i s and  3.2 cm i n t h e r a d i a l d i r e c t i o n and s t a r t e d on t h e a x i s 3 mm from t h e f a c e o f t h e magnets. Before each scan, t h e o f f s e t o f t h e a m p l i f i e r was a d j u s t e d to  c a n c e l the e f f e c t s o f the e a r t h ' s magnetic f i e l d  zero o f f s e t .  and any  The magnetic c o n f i g u r a t i o n was then p l a c e d i n  Experimental R e s u l t s / 50 the  holder  and  repeatability.  the d e t e c t o r  positioned  manually  The s t a r t i n g p o s i t i o n was  to  ensure  approached i n the  same d i r e c t i o n o f motion as t h a t o f the d a t a c o l l e c t i o n  to  a v o i d any problems r e s u l t i n g from b a c k l a s h . A f t e r the data was c o l l e c t e d , i t was p r o c e s s e d to the  produce magnetic f i e l d l i n e s p l o t s .  then i n t e g r a t e d a l o n g the r a d i u s a t each  p o s i t i o n through the use o f Simpson's middle v a l u e f o r each added " s t r i p " .  of  The n o n - l i n e a r i t y o f  d e t e c t o r was c o r r e c t e d f o r through c u b i c s p l i n e i t e r a t i o n .  The d a t a was  for  i n order  axial  Rule which r e q u i r e s a  T h i s produced t h e v a l u e s  the imaginary magnetic s c a l e r p o t e n t i a l f o r a 1 mm  grid  2  64 by 32 mm.  The p o t e n t i a l f i e l d was  r e f l e c t e d about the  magnetron a x i s , then added t o the o r i g i n a l f o r the purpose o f presentation.  3.  F i e l d Line Plots The magnetic  presented i n  field  F i g s 5.1  l i n e s of configurations through  5.5.  are  As d i s c u s s e d i n Chapter  3, these a r e a c t u a l l y the contours o f T . m  the  1 to 5  A c r o s s - s e c t i o n of  magnets i s a l s o presented shown both t o s c a l e and i n i t s  position  relative  t o the f i e l d .  For the purpose  of  later  arguments, the p o s i t i o n s o f the t a r g e t used i n t h e s p u t t e r i n g run  a r e a l s o shown.  These have been  l i n e s above the magnetron. thick  r e p r e s e n t e d by  In each case the t a r g e t i s 3  expect f o r magnetron 5, where a 8 mm  displayed.  dotted  target  mm  i s also  For magnetron 1 the placement o f the ground s h i e l d  Experimental R e s u l t s /  F i g u r e 5.1 Magnetron 1. This configuration i s used i n c o n v e n t i o n a l magnetron s p u t t e r i n g . Shown a l s o i s the ground s h i e l d c o n f i g u r a t i o n .  F i g u r e 5.2 Magnetron 2. The s t r e n g t h o f the c e n t r e magnet has been reduced t o 50% o f t h a t o f magnetron 1.  Experimental R e s u l t s /  F i g u r e 5.3 Magnetron 3. The s t r e n g t h o f t h e c e n t r e magnet has been reduced t o 25% o f t h a t o f magnetron 1.  F i g u r e 5 . 4 Magnetron 4. Here the c e n t r e has been r e p l a c e d by a m i l d s t e e l p i e c e .  magnet  Experimental R e s u l t s / 53  F i g u r e 5 . 5 Magnetron 5. The annular magnet i s r e p l a c e d by one o f a g r e a t e r s t r e n g t h . used d u r i n g a s p u t t e r i n g run i s presented. The f l u x between the f i e l d l i n e s i s c o n s t a n t f o r a l l f i v e plots,  5 x 10" Wb. 6  T h i s was achieved p a r t i a l l y by a s s i g n i n g  e q u a l l y spaced v a l u e s f o r the contours. taken,  however,  as  the  r e f l e c t e d about the a x i s .  imaginary  E x t r a c a r e had t o be  scaler  The v a l u e of  T  potential  was  on t h e a x i s was  m  zero.  To  satisfy  the requirement  that  flux  was  constant  between t h e f i e l d l i n e s , the p o s i t i v e and n e g a t i v e v a l u e s were equally  spaced  about  zero.  The  flux  between  the  first  p o s i t i v e contour, which was the f i r s t t o r e t u r n the r e a r o f the magnetron, and the a x i s was then h a l f o f t h a t between the contour  lines.  The  flux  between  this  field  line  and i t s  r e f l e c t i o n was then equal t o the f l u x between the o t h e r  field  Experimental  Results /  54  400 <a  Cl  -400  A -4->  6C  <"  -800  M  W  3  -1200  QJ  • rH  .a - i 6 o o QJ  PI  «>-2000  s  -2400  0  F i g u r e 5.6  5  10  15  20  25 30 35 40 Position (cm)  45  50  55  60  65  Magnetic f i e l d s t r e n g t h along the a x i s f o r magnetrons 1 to 5. The i n s e t shows an i n c r e a s e d s c a l e f o r the f i e l d .  lines. The is  a x i a l component of the magnetic f i e l d a l o n g the a x i s  shown i n F i g . 5.6.  As  the  t h i s i s the s t r e n g t h of the  radial  component here i s zero  field.  When the magnetic f i e l d i s v i s u a l i z e d i n t h r e e  dimensional  space, the f i e l d l i n e s are r o t a t e d about the a x i s , r a t h e r than extended outwards from the page as i n a c a r t e s i a n c o o r d i n a t e system. as  T h i s does c r e a t e some d i f f i c u l t y i n i n t e r p r e t a t i o n ,  equally  spaced  field  lines  away  from  r e p r e s e n t a constant magnetic f i e l d due t o in  Eq.  3.12.  arguments.  This  i s taken  the  axis  do  not  the r a d i a l f a c t o r  into considerations  in  later  Experimental 4.  Results /  55  Plasma Probe Measurements The  charged  particle  flux  resulting  magnetrons 1 through 5 i n a s p u t t e r run was  from  the  use  of  measured w i t h  the  apparatus d e s c r i b e d i n Chapter 4. Each First  of  the  the  experiments were  detector  was  placed  in  r e l a t i v e t o the magnetron f a c e .  face  once  the  p o s i t i o n i n g process, enough  preventing  to any  g r a v i t y . The  the  position fastened  i n i t i a l l y p o s i t i o n e d t o the  door  was  door was  respect to  closed.  During  raised until  allow  f o r measurement  error  arising  probe was  same manner.  i t s starting  T h i s , i n t u r n , would p o s i t i o n i t with  magnetron  just  i n the  As the assembly was  t o the chamber door, the probe was door.  run  from  a  the  i t was  i n s i d e the shifting  the  open  chamber, centre  of  then p r o p e r l y p o s i t i o n e d i n the same  d i r e c t i o n of motion i t would take d u r i n g the s p u t t e r i n g run t o avoid  problems w i t h  backlash.  The  chamber was  pumped down t o p r e s s u r e of approximately gas was The the  5 X 10"  closed  and  Torr.  Argon  a t 2 00 mA  during  5  then i n t r o d u c e d a t a p r e s s u r e o f 1 Pa. d i s c h a r g e c u r r e n t was  run.  A  copper  target,  h e l d constant 3  mm  thick,  was  employed.  Measurements were taken a t 1 cm i n t e r v a l s along the magnetron a x i s from 3 t o 11 The average  cm.  data  c o l l e c t e d a t each a x i a l p o s i t i o n i n c l u d e d both  and  spatial  information.  The  ground  current  measured f o r both the l a r g e and the s m a l l c e n t r a l probe. should  be  noted t h a t when measurements i n v o l v i n g the  was It  large  Experimental R e s u l t s / 56 probe were taken, the s m a l l e r probes were a l s o i n c l u d e d i n the circuit.  The  probes  were  then  determine the f l o a t i n g p o t e n t i a l .  isolated  electrically  F i n a l l y a -100V  bias  to was  a p p l i e d and the i o n c u r r e n t s were measured f o r both the e n t i r e system and each o f the s m a l l e r probes. In  Chapter 1 i t was  ground s h i e l d was the  discharge.  d i s c u s s e d how  the placement  a l s o an important f a c t o r i n the nature o f  For magnetron 1 two ground s h i e l d s were used.  The f i r s t , r e f e r r e d t o as the r e s t r i c t i v e s h i e l d , the  field  o f the  intersected  l i n e s between the annular and c e n t r e magnet.  second, r e f e r r e d t o as the open s h i e l d ,  was  from  configuration  these  field  lines.  The  second  The  c u t back away was  converted t o the f i r s t through the a d d i t i o n o f a l i p i n i t s opening.  The opening o f the second c o n f i g u r a t i o n and the l i p  are  shown i n F i g . 5.1.  When the p a r t i c l e f l u x e s were examined  for  magnetrons 2 t o 5 the open s h i e l d was  5. R e s u l t s f o r the Large Plasma  always used.  Probe  R e s u l t s from the measurements taken a t an a x i a l of  distance  6 and 10 cm w i t h the l a r g e plasma probe are shown i n T a b l e  5.2.  A s e t o f r e s u l t s are d i s p l a y e d f o r Magnetron  ground s h i e l d The  configuration.  discharge voltage  s t r e n g t h was  1 f o r each  increased  as the c e n t r e magnet's  reduced, w h i l e the a n n u l a r magnet was c o n s t a n t .  The use o f magnetron 5 decreases the power requirements t o below t h a t o f magnetron 1. The probe c o l l e c t s about h a l f o f  Experimental R e s u l t s / 57 T a b l e 5.2  D i s c h a r g e c h a r a c t e r i s t i c s measured by t h e l a r g e p r o b e f o r m a g n e t r o n s 1 t o 5.  1 (res.) 1 (open) 2 3 4 5  the  Disch. Voltage (V)  Probe selfbias (V)  6  334  -17.0  94  -2.9  10  332  -15.6  76  -2.6  6  332  -20.1  190  -9.0  10  334  -15.3  136  -5.3  6  342  -20.0  193  -9.8  10  345  -14.8  144  -4.9  6  361  -20.0  193  -10.3  10  361  -14.0  151  -5.0  6  397  -20.5  200  -13 . 6  10  397  -10.7  151  -6.3  6 10  307 310  -29.8 -17.7  200  -39.1 -18.4  Axial Dist. (cm)  Magnet. Config.  discharge  current  at  6 cm  Probe ground current (mA)  Probe - 100 V current (mA)  190  f o r magnetron  1 with the  r e s t r i c t i v e s h i e l d but n e a r l y a l l w i t h t h e open c o n f i g u r a t i o n . All  or nearly  collected  at  a l l of the discharge this  position  current  f o r the  (200 mA)  remainder  of  is the  magnetrons.  6. R e s u l t s  f o r the Small  Probes.  The r e s u l t s f o r t h e s m a l l e r probes a r e shown i n F i g s . 5.7 t o 5.10.  F i g . 5.7 d i s p l a y s  magnetron c o n f i g u r a t i o n s .  t h e ground c u r r e n t s f o r t h e  five  In F i g . 5.8 t h e i o n c u r r e n t s a r e  d i s p l a y e d along t h e a x i s f o r each o f t h e magnetron assemblies. For  Figs.  5.9  and 5.10  the r a d i a l  dependence  of the i o n  c u r r e n t s a r e shown f o r magnetrons 1 and 5 r e s p e c t i v e l y .  Experimental R e s u l t s / 58  o  •  Position  5 4  (cm)  F i g u r e 5.8 Ion c u r r e n t s t o the s m a l l a l o n g the a x i s f o r magnetrons 1 t o 5.  central  detector  Experimental R e s u l t s / 59  o • A  0.00  4 cm 7 cm 10 cm  2 3 Position (cm)  F i g u r e 5.9 R a d i a l dependence o f the i o n c u r r e n t s f o r magnetron 1. The data i s shown f o r an a x i a l d i s t a n c e o f 4, 7, and 10 cm.  F i g u r e 5.10 R a d i a l Dependence of the i o n c u r r e n t s f o r magnetron 5 a t a x i a l d i s t a n c e s o f 4, 7, and 10 cm.  Experimental R e s u l t s / 60 7.  Discussion Figs.  5.1  through  5.6  demonstrate  c o n f i g u r a t i o n a f f e c t s t h e magnet f i e l d .  how  the  magnetic  The d i f f e r e n c e s i n  the f i e l d between t h e magnetrons can be observed p r i m a r i l y i n two r e g i o n s .  The f i r s t  r e g i o n i s t h e magnetic t u n n e l  which  c o n s i s t s o f those f i e l d l i n e s going between t h e annular magnet and t h e c e n t r e magnet.  The second r e g i o n i s a magnetic f u n n e l  caused by t h e c o n s t r i c t i o n o f f i e l d l i n e s about t h e magnetron axis. The  magnetic t u n n e l s u s t a i n s t h e primary d i s c h a r g e .  As  the magnetron becomes i n c r e a s i n g l y unbalanced from 1 and 4, both t h e r e l a t i v e amount o f f i e l d l i n e s i n t h e t u n n e l and the extent o f t h e t u n n e l from the t a r g e t s u r f a c e decreases.  When  the  from  inner  radius  o f t h e annular  magnet  i s increased  magnetron 4 t o 5, t h e o v e r a l l f l u x i s i n c r e a s e d and a g r e a t e r number o f f i e l d l i n e s i n the t u n n e l i s observed. t u n n e l extends approximately  However the  the same d i s t a n c e from t h e t a r g e t  s u r f a c e as b e f o r e . The  tunnel  a c t s t o c o n t a i n the d i s c h a r g e  where t h e f i e l d  lines  are p a r a l l e l  through magnetic b o t t l e e f f e c t s .  i n the region  t o the t a r g e t  surface  The confinement i s due t o  the f i e l d s t r e n g t h being g r e a t e r along t h e t u n n e l f i e l d i n the proximity  lines  o f t h e annular magnet and magnetron c e n t r e  than i n t h e r e g i o n where t h e f i e l d l i n e s a r e p a r a l l e l t o the target. A  set  of  investigations  were  done  to  examine  the  Experimental R e s u l t s / 61 effectiveness  o f the tunnel  f o r both  primary  trapping  c o n f i n i n g t h e e l e c t r o n s i n t h e r e g i o n where t h e f i e l d are p a r a l l e l t o t h e t a r g e t s u r f a c e . looked  at the r a t i o  and lines  The f i r s t i n v e s t i g a t i o n  o f the d i s t a n c e  t o which  an  emitted  e l e c t r o n would i n i t i a l l y t r a v e l from t h e t a r g e t between t h e different  magnetron  configurations,  i n order  t o give  an  i n d i c a t i o n o f t h e r e l a t i v e e f f e c t i v e n e s s o f t h e primary t r a p s . If  we assume t h a t t h e e l e c t r o n t r a v e l s beyond t h e p o s i t i v e  space charge value  i n front of the target  and t h a t  the absolute  o f t h e plasma p o t e n t i a l i s much l e s s than t h a t o f t h e  d i s c h a r g e v o l t a g e then, from equation 2.12, distances  the r a t i o  o f the  f o r two magnetrons i s approximately (5.1)  The d i s c h a r g e v o l t a g e i n c r e a s e s by approximately 25 % between magnetrons 1 and 4 w h i l e the f i e l d s t r e n g t h i n t h e v i c i n i t y o f the t a r g e t drops by about h a l f .  Therefore,  t o 4, we would expect the emitted from  the target.  electrons  e l e c t r o n s t o extend f u r t h e r  F o r magnetron  t o be contained  from magnetrons 1  largely  5  we  would  i n t h e same  expect the region  as  magnetron 1. The next i n v e s t i g a t i o n examined the r e l a t i v e e f f e c t i v e n e s s o f the t u n n e l region  f o r each magnetron t o c o n f i n e e l e c t r o n s t o the  where t h e f i e l d  surface.  lines  I t was d i f f i c u l t  were p a r a l l e l  t o the target  t o compare the magnetic m i r r o r i n  the v i c i n i t y o f t h e magnetron c e n t r e , as, though t h e f i e l d i n  Experimental R e s u l t s / 62 the  region  unbalanced  of the discharge cases,  was  decreasing  so was t h e f i e l d  f o r t h e more  a t t h e magnetron c e n t r e .  For magnetron 5, however, t h e f i e l d i n t h e d i s c h a r g e r e g i o n i s approximately  t h a t o f magnetron 1 w h i l e  f i e l d i s l e s s a t t h e magnetron c e n t r e .  from T a b l e  Therefore  5.1 t h e  the tunnel  of magnetron 5 i s l e s s e f f e c t i v e i n c o n t a i n i n g e l e c t r o n s from the c e n t r e r e g i o n . For magnetrons 1 t o 4, the f i e l d s t r e n g t h i n t h e v i c i n i t y of t h e annular magnet i s approximately c o n s t a n t .  As t h e f i e l d  s t r e n g t h i n t h e r e g i o n o f the d i s c h a r g e decreases f o r t h e more unbalanced  cases,  effective  the  f o r the  configurations. confinement  annular  more  balanced  For magnetron  region  mirror  magnetrons  5,  the f i e l d  i s approximately  magnetron 1, however t h e f i e l d greater.  magnetic  is for  less these  i n t h e main  t h e same  as t h a t f o r  i n t h e annular r e g i o n i s much  T h e r e f o r e , t h e annular magnetic m i r r o r o f magnetron  1 i s l e s s e f f e c t i v e than t h a t f o r magnetron 5. With t h e open ground s h i e l d c o n f i g u r a t i o n , t h e d i s c h a r g e e l e c t r o n s can escape both from the r e g i o n s i n t h e v i c i n i t y o f the annular magnet and from the magnetron c e n t r e . for  t h e more  unbalanced  magnetrons  Therefore  t h e e l e c t r o n s have  a  g r e a t e r p r o b a b i l i t y o f escape along t h e magnetron a x i s . The  magnetic  f u n n e l becomes more c o n s t r i c t e d  a x i s as t h e magnetron becomes more unbalanced. with  the greater  escaping  along  probability  t h e magneton  of  T h i s , combined  the d i s c h a r g e  axis,  should  about t h e  electrons  result  i n the  Experimental Results / 63 discharge  current  conditions.  becoming  more  focused  under  these  From Table 5.2 i t can be seen t h e l a r g e d e t e c t o r  c o l l e c t s a l l or p r a c t i c a l l y a l l of the discharge current at 6 cm along t h e magnetron a x i s . at t h i s point the discharge  In F i g 5.7 i t can be seen t h a t c u r r e n t i s becoming more  focused  about t h e a x i s as p r e d i c t e d . Table 5.2 shows t h a t t h e o v e r a l l i o n c u r r e n t t o t h e l a r g e d e t e c t o r i n c r e a s e s as the magnetron becomes more unbalanced. From Eq. 2.2, i t i s shown t h a t the i o n c u r r e n t s e i t h e r the density  o f the plasma i n c r e a s e s  increase i f  or the e l e c t r o n  temperature i n c r e a s e s .  From Eq. 2.3,  potential  o n l y magnetron 5 shows a s i g n i f i c a n t  increase  i s constant,  i n e l e c t r o n temperature.  and assuming t h e plasma  I t i s p o s s i b l e t h a t the  e l e c t r o n temperature i s r i s i n g s l i g h t l y from magnetrons 1 t o 4 as t h e plasma p o t e n t i a l i s not known and Eq. 2.4 i s o n l y an approximation.  However, because o f the square r o o t dependence  o f t h e i o n c u r r e n t on e l e c t r o n temperature, t h i s dominant  f a c t o r i n any o f t h e cases.  i s not t h e  Therefore  i t would  appear t h a t the i n c r e a s e i n i o n c u r r e n t i s l a r g e l y due t o an i n c r e a s e i n t h e plasma d e n s i t y i n t h e r e g i o n o f t h e probe. A  possible  explanation  f o r the small  increases  i n ion  c u r r e n t f o r magnetrons 1 t o 4 i s t h a t t h e primary d i s c h a r g e i s contained cases.  further Though  from  the target  t h e probe  i n t h e more  i s a t t h e same  unbalanced  p o s i t i o n on t h e  magnetron a x i s , i t i s c l o s e r t o t h e a c t u a l d i s c h a r g e o v e r a l l plasma d e n s i t y i s g r e a t e r .  and t h e  Experimental Results / 64 An  i n c r e a s e d plasma d e n s i t y i n t h e v i c i n i t y o f t h e probe  c o u l d a l s o be due t o i o n g e n e r a t i o n the magnetic t u n n e l .  i n t h e r e g i o n away from  One p o s s i b l e mechanism f o r t h i s i n c r e a s e  i s a more e n e r g e t i c e l e c t r o n f l u x d i f f u s i n g from t h e t u n n e l . The  higher  energy  electrons  have a g r e a t e r  p r o b a b i l i t y of  i n d u c i n g i o n i z a t i o n on t h e i r path t o the d e t e c t o r .  From Table  5.2 i t can be seen t h a t from magnetrons 1 t o 4 t h e d i s c h a r g e v o l t a g e i s i n c r e a s i n g , i n d i c a t i n g t h a t the primary t r a p p i n g i s less efficient. at  The f l o a t i n g p o t e n t i a l f o r magnetrons 1 t o 4  6 cm does not, however,  i n d i c a t e a much more  electron flux i n t h i s region. potential  For magnetron 5, t h e f l o a t i n g  i n d i c a t e s a more e n e r g e t i c  vicinity  of the detector,  through  less  efficient  energetic  electron  however t h i s trapping  as  flux  cannot be the  tunnel  i n the  explained i s more  e f f i c i e n t than t h a t f o r magnetron 4. An  i n c r e a s e plasma d e n s i t y  i n the v i c i n i t y  c o u l d a l s o be due t o i o n g e n e r a t i o n the magnetic t u n n e l .  Window e t a l .  o f the probe  i n t h e r e g i o n away from 5  have suggested t h a t a  secondary d i s c h a r g e c o u l d be contained by a magnetic b o t t l e i n the f u n n e l r e g i o n .  The magnetic f i e l d measurements performed  i n t h i s t h e s i s a r e c o n s i s t e n t with a magnetic b o t t l e i n t h i s region. magnetic  F i g . 5.11 shows t h e f i e l d s t r e n g t h along one o f t h e field  lines  i n t h e funnel  There i s a l o c a l minimum, B  2  region  and a l o c a l  near  the axis.  maximum, B . 3  The  magnitude o f B decreases f o r f i e l d l i n e s c l o s e r t o t h e a x i s . 2  The  spatial  extent  o f t h e secondary magnetic b o t t l e was  Experimental R e s u l t s / 65 300 (j->  to ZD  200  X  Ld Cd  — I CO  o  100  o ti  <  DISTANCE A L O N G FIELD LINE ( c m )  F i g u r e 5.11  Magnetic f i e l d s t r e n g t h a l o n g a secondary magnetic b o t t l e f i e l d l i n e .  investigated  for configurations  1,  4,  and  5.  The  field  s t r e n g t h a l o n g the f i e l d l i n e s was determined through the use of  a computer program  written f o r t h i s task.  The  criterion  f o r a f i e l d l i n e t o be c o n s i d e r e d p a r t o f the secondary b o t t l e was t h a t B  2  was a t l e a s t 2 0% l e s s than B  The r e s u l t s showed  3  t h a t as the magnetron became more unbalanced, the secondary magnetic  bottle  p o s i t i o n of B the  2  closer  same as where the f i e l d  local  b o t t l e was target.  to  the  target.  The  axial  f o r each magnetron was, t o w i t h i n a m i l l i m e t r e ,  absolute value of the  moved  was,  went t o zero i n F i g 5.6.  t o w i t h i n a few Gauss,  maximum i n F i g 5.6.  The  shape  The  the same as  o f the  secondary  r o u g h l y a cone w i t h the wider end c l o s e s t t o the  An i n t e r e s t i n g r e s u l t was t h a t the s p a t i a l dimensions  Experimental R e s u l t s / 66 of  the secondary magnetic b o t t l e was p r a c t i c a l l y the same i n  each case.  For magnetron 1 the dimensions were a l a r g e  s m a l l r a d i u s o f approximately 8 and 6 mm magnetron  5 approximately 7 and  5 mm.  r e s p e c t i v e l y and f o r The  secondary b o t t l e a l o n g the magnetron a x i s was 1.2  and  length  o f the  approximately  cm. U n l i k e the t u n n e l , the secondary magnetic b o t t l e must be  s u p p l i e d w i t h e n e r g e t i c e l e c t r o n s from another source; i . e . , from  the  primary  discharge.  The  magnitude  g e n e r a t i o n i n the funnel r e g i o n i s dependant,  of  plasma  therefore,  on  the a b i l i t y o f the f i e l d t o channel e l e c t r o n s from the t u n n e l t o the b o t t l e ,  the a b i l i t y  o f the b o t t l e t o t r a p  electrons  above the i o n i z a t i o n t h r e s h o l d o f the s p u t t e r i n g gas, and the a v a i l a b i l i t y o f e l e c t r o n s w i t h the r e q u i r e d  energy.  T y p i c a l e l e c t r o n e n e r g i e s f o r the d i s c h a r g e from e f f i c i e n t magnetrons such as 1 are i n the range from 2 t o 5 eV . should  be  efficient  expected the  that  average  as  the  electron  magnetron  19  It  becomes  less  temperature  increases.  T h e r e f o r e t h e r e are e l e c t r o n s w i t h e n e r g i e s s u f f i c i e n t ionization  f o r a l l o f the magnetons used i n t h i s  for  section.  The s p a t i a l e x t e n t o f the magnetic m i r r o r i s approximately the same f o r a l l the magnetrons used  in this  section.  The  f u n n e l l i n g o f the d i s c h a r g e then f a v o u r s l a r g e r i o n g e n e r a t i o n i n the secondary magnetic b o t t l e as the magnetron becomes more unbalanced. As mentioned p r e v i o u s l y , the maximum energy t h a t a trapped  Experimental Results / 67 e l e c t r o n can  possess i n the secondary magnetic b o t t l e i s an  important f a c t o r i n i o n g e n e r a t i o n .  shows t h a t  the  o r b i t a l r a d i u s i s dependant on both the e l e c t r o n energy  and  the  magnitude  should  not  of  be  the  magnetic  l a r g e r than the  Eq.  2.6  field.  The  orbital  dimensions o f  the  radius  secondary  magnetic b o t t l e . To  determine  energy  that  approximately  could  be  trapped  what the  the  maximum  criterion  was  electron that  the  e l e c t r o n o r b i t a l r a d i u s c o u l d not be l a r g e r than the minimum r a d i u s o f the secondary b o t t l e . magnetic trapped 11,  field  value,  the  Using the v a l u e of B  maximum e n e r g i e s  that  3  f o r the  could  f o r magnetrons 1, 2, 3, 4, and 5 were found t o be  17,  25,  and  175  eV  respectively.  Notwithstanding  approximation used, i t i s e v i d e n t t h e r e i s in trapping e f f i c i e n c y  i n going  a large  be 7, the  increase  from magnetron 4 t o 5.  i n c r e a s e d t r a p p i n g i s expected t o r e s u l t i n an i n c r e a s e d  This ion  density. Three o t h e r f a c t o r s l e n d support t o an e f f e c t i v e  ionizing  mechanism away from the primary d i s c h a r g e f o r magnetron 5.  The  first  i s the  greater  the  lower  probe  self  e l e c t r o n temperature  bias  in  Table  5.2.  i n d i c a t e d by  This  indicates  the  presence of a plasma d i s c h a r g e c l o s e r t o the probe. Secondly, magnetron 5 has despite  no  tunnel.  This  generated  a lower d i s c h a r g e  i n d i c a t i o n of  in  can the  be  having  explained  secondary  by  voltage a  more  than magnetron 1 effective  a proportion  magnetic  bottle  of  primary the  ions  drifting  back  Experimental Results / 68 towards the t a r g e t and h e l p i n g t o support third  f a c t o r i s the decrease i n i o n c u r r e n t  o n l y i n F i g . 5.8. 2.5  cm.  The a x i a l p o s i t i o n of B  f o r magnetron 5  i s a t approximately the  discharge.  C. CENTRE PIECE GEOMETRY AND  TARGET THICKNESS EFFECTS  Introduction From the d i s c u s s i o n s i n p a r t B,  the  3  The  T h i s i n d i c a t e s t h a t the probe i s i n t e r f e r i n g w i t h  secondary  1.  the d i s c h a r g e .  ion  current  that  bombards  i t became apparent t h a t  the  substrate  was  largely  dependant on the development of the secondary magnetic b o t t l e away from the t a r g e t .  Attempts were made t o change the  field  c o n f i g u r a t i o n through a l t e r i n g the geometry of the c e n t r e p o l e piece.  Another mechanism used  to  alter  the  magnetic  field  c o n f i g u r a t i o n was t o change the t h i c k n e s s of the t a r g e t . would a l t e r the magnetic t u n n e l but not the The  r e s u l t s f o r two  configurations thicknesses  are  target thicknesses  shown i n t h i s  were 3 and  8 mm.  The  This  funnel. and  section.  two  The  magnetron two  target  f i r s t magnetron used  was  The second, magnetron 6,  had  the same annular magnet and the base of the c e n t r e p i e c e  was  magnetron 5 of the l a s t s e c t i o n .  the same as t h a t f o r magnetron 5, however, a t 0.32 the a x i s , magnetron 6's  centre piece tapers  comes t o a p o i n t . The d i s t a n c e 0.64  cm.  of the p o i n t  cm  along  inward u n t i l i t from the base i s  Experimental R e s u l t s / 69  F i g u r e 5.12 Magnetron 6  -2400  10  -120  15 20 25 30 35 40 45 50 55 60 65 Position (cm)  F i g u r e 5.13 Magnetic f i e l d magnetrons 5 and 6.  strength  along  the a x i s f o r  Experimental Results / 70 T a b l e 5.3  Results f o r the large probe for c o n f i g u r a t i o n s 5 and 6 w i t h a 3 and 8  Probe  Probe  magnetic mm t a r g e t .  Probe  Magnet.  Axial  Disch.  self-  ground  - 100 V  Config.  Distance  Voltage  bias  current  current  (cm)  (V)  (V)  (mA)  (mA)  6  -307  -29.8  200  -39.1  10  -310  -17.7  190  -18.4  6  -320  -26.7  198  -34.3  10  -320  -12.3  185  -12.4  6  -501  -23.6  198  -28.8  10  -506  -11.7  187  -14.1  6  -635  -25.0  200  -48.7  10  -629  -11.1  189  -24.6  5 3 mm 6 3  mm 5  8  mm 6  8  mm  J  3  4  I  I  5  I  I  I  6  7 8 Position (cm)  I  I  I  i  1  9  I  L  10  11  12  F i g u r e 5.14 Ground c u r r e n t s t o the c e n t r a l d e t e c t o r along the magnetron a x i s f o r magnetrons 5, 6 f o r t a r g e t t h i c k n e s s e s o f 3 and 8 mm.  Experimental Results / 71  7  0  6, 5, 6, 5,  3  4  5  6  7 8 Position (cm)  9  10  8 mm 8 mm 3 mm 3 mm  11  12  F i g u r e 5.15 Ion c u r r e n t s along t h e a x i s f o r magnetrons 5, 6 f o r t a r g e t t h i c k n e s s e s o f 3 and 8 mm.  2. E x p e r i m e n t a l  Results  The f i e l d r e s u l t i n g from magnetron 6 i s d i s p l a y e d i n F i g . 5.12.  Both t a r g e t t h i c k n e s s a r e d i s p l a y e d i n t h e same manner  as t h a t f o r magnetron 5.  The magnetic f i e l d along t h e a x i s i s  shown i n F i g . 5.13 f o r magnetrons 5 and 6.  The r e s u l t s f o r  the l a r g e probe a r e presented i n Table 5.3 and f o r t h e small c e n t r a l probe i n F i g s . 5.14 and 5.15  3.  Discussion  There i s l i t t l e d i f f e r e n c e i n the magnetic f u n n e l between 5 and 6. minimum  The main d i f f e r e n c e appears t h a t f o r magnetron 6 the o f t h e funnel  i s two  millimetres  closer  t o the  Experimental R e s u l t s / 72 magnetron.  The t u n n e l  o f magnetron 6 c o n t a i n s  fewer  field  l i n e s than t h a t o f magnetron 5 and extends out from t h e face by a l e s s d i s t a n c e .  The f i e l d s t r e n g t h along t h e l a s t  field  l i n e o f t h e t u n n e l i s t h e same f o r both magnetrons t o w i t h i n a few p e r c e n t . The  secondary  magnetic  bottle  has  the  same  spatial  dimensions f o r both magnetrons w i t h t h a t o f magnetron 6 b e i n g 2 mm  c l o s e r t o t h e magnetron.  electrons  that  can be c o n f i n e d  The maximum energy  of the  i n the b o t t l e i s s l i g h t l y  h i g h e r than t h a t f o r magnetron 5 as i n d i c a t e d i n F i g . 5.13. The  most  interesting  result  i s that  f o r a 3 mm  thick  t a r g e t , magnetron 5 i s t h e most e f f e c t i v e i n producing w h i l e f o r a 8 mm t h i c k t a r g e t i t i s magnetron 6. the  larger  i o n generation  i s from  ions  In each case  the magnetron  with t h e  g r e a t e r d i s c h a r g e c u r r e n t along t h e a x i s ( F i g . 5.14). For t h e 3 mm t a r g e t , t h e d i s c h a r g e v o l t a g e s i n both cases are low, i n d i c a t i n g e f f e c t i v e primary t r a p p i n g . generates more i o n c u r r e n t mentioned  previously  this  than  that  appears  Magnetron 5  o f magnetron  t o be due t o a  6.  As  greater  d i s c h a r g e c u r r e n t along the magnetron a x i s . As t h e funnel appears t o be o f the same width f o r both magnetrons, difference  the tunnel i n discharge  i s most currents  likely  responsible  long t h e a x i s .  f o r the  From F i g .  5.13 i t can be seen t h a t t h e s t r e n g t h o f t h e magnetic f i e l d i n the v i c i n i t y o f t h e c e n t r e i s approximately magnetrons.  t h e same f o r both  However, due t o t h e r e d u c t i o n i n h i g h permeable  Experimental R e s u l t s / 73 m a t e r i a l i n t h e c e n t r e p i e c e o f magnetron 6 along t h e edges, the f i e l d and  s t r e n g t h i s l e s s i n t h e r e g i o n between t h e c e n t r e  annular  magnet c l o s e t o t h e t a r g e t s u r f a c e .  the d i s c h a r g e target. that  f o r magnetron 6 w i l l  extend  Therefore,  f u r t h e r from t h e  T h i s w i l l be a r e g i o n o f a weaker magnetic f i e l d than  f o r magnetron 5 and the magnetic t u n n e l  e f f e c t i v e i n keeping t h e d i s c h a r g e The  magnetic  tunnel  will  be more  from t h e c e n t r e .  becomes much  less  efficient for  magnetron 5 when the 8 mm t a r g e t i s employed and even more so f o r magnetron 6.  These f a c t o r s a r e i n d i c a t e d by t h e d i s c h a r g e  v o l t a g e s shown i n Table 5.3. discharge  A l s o , f o r both magnetrons, t h e  c u r r e n t along t h e a x i s i s much l a r g e r than i n t h e  case w i t h t h e 3 mm t a r g e t . The i n e f f i c i e n t t r a p p i n g and t h e l a r g e d i s c h a r g e c u r r e n t s along t h e a x i s i n d i c a t e t h a t t h e d i s c h a r g e i s b e i n g  supported  more by t h e secondary d i s c h a r g e than when the 3 mm t a r g e t i s employed.  T h i s c o u l d e x p l a i n why t h e i o n c u r r e n t i s g r e a t e r  f o r magnetron 6. relies  more on t h e secondary  evident factor  As magnetron 6 i s much l e s s e f f i c i e n t , i t  from the g r e a t e r i s t h a t with  discharge  axial  discharge  the l a r g e r d i s c h a r g e  than  5.  This i s  current.  Another  voltage  and l e s s  e f f i c i e n t t r a p p i n g , t h e average energy o f t h e e l e c t r o n s which escape t h e primary t r a p i s g r e a t e r . The  t o t a l i o n c u r r e n t i s l e s s f o r magnetron 5 than when  a 3 mm  t a r g e t i s used.  overall  plasma d e n s i t y  A possible explanation i s less.  i s that the  With the h i g h e r  discharge  Experimental R e s u l t s / 74 voltage,  the ions impacting upon the t a r g e t w i l l produce more  secondary  electrons.  T h e r e f o r e the  o v e r a l l plasma  density  r e q u i r e d t o s u s t a i n the d i s c h a r g e i s l e s s .  D.  PLASMA CHARACTERISTICS OF  1.  UNBALANCED MAGNETRONS  Introduction  The  purpose of t h i s s e c t i o n was  t o examine the  c h a r a c t e r i s t i c s f o r magnetron 5 under a number of conditions.  The  2.  Target  Two  p r e s s u r e and  C w h i l e the t a r g e t  same  material,  d i s c h a r g e c u r r e n t were v a r i e d .  Material  target  compositions  g r a p h i t i c carbon.  were  The p r e s s u r e was  the d i s c h a r g e c u r r e n t was The  sputtering  p a r t i c l e f l u x e s were measured i n the  method as t h a t of s e c t i o n B and s p u t t e r i n g gas  discharge  100  discharge voltage  examined,  copper  h e l d c o n s t a n t at 1 Pa.  and and  mA.  increased  from 500  copper t a r g e t t o 650 v o l t s f o r the carbon.  volts  T h i s i s due  for  the  t o the  decreased v a l u e of the secondary e l e c t r o n e m i s s i o n c o e f f i c i e n t for  carbon.  The  difference  measurements were w i t h i n 5%).  Therefore,  characteristics  to  appear  materials.  Similar  copper and  silicon . 1 4  between  the  experimental within  these  independent  results  have  remainder  error  also  the  plasma  two  target  noted  between  these been  the  (approximately  bounds, for  of  Experimental R e s u l t s / 75  0 5  i  i  L  " 0.5  i  i  1.0  i  i  1.5  i  2.0  2.5  L o g of D i s c h a r g e C u r r e n t  F i g u r e 5.16 Logarithmic p l o t of i o n c u r r e n t s t o the c e n t r a l probe versus d i s c h a r g e c u r r e n t . Magnetron 5 is used w i t h an 8 mm carbon t a r g e t . The probe i s p o s i t i o n e d a t a d i s t a n c e o f 6 cm along the magnetron a x i s .  3.  Discharge  Current  The d i s c h a r g e c u r r e n t was mA.  The p r e s s u r e was  v a r i e d over a range of 7 t o  150  h e l d constant a t 1 Pa and the probe  was  p o s i t i o n e d 6 cm along the magnetron a x i s .  A logarithmic plot  of the i o n c u r r e n t from the s m a l l c e n t r a l d e t e c t o r b i a s e d a t 100  V versus  discharge  current  i s shown i n F i g . 5.16.  r e s u l t s were p l o t t e d l o g a r i t h i m i c a l l y t o p r e s e n t lower d i s c h a r g e c u r r e n t s more c l e a r l y . normalized  which, on  the  data.  the data at  The r e s u l t s were a l s o  a logarithmic plot,  s h i f t i n g the y - i n t e r c e p t o n l y .  The  has  A l i n e a r f i t was  the  effect  of  i n c l u d e d with  Experimental R e s u l t s / 76 The  f i t appears  approximately along  the  unity.  to  be  reasonable  This  magnetron a x i s  4.  are  directly  slope  ion  of  currents  proportional to  the  These r e s u l t s compare w e l l  14.  p r e s s u r e was  discharge  The watts,  varied  c u r r e n t was  The probe was  over the range of  50 mA.  and  as  observed  to 2  the t a r g e t was  the  pressure  increased.  This  is  due  carbon.  to  i o n i z a t i o n c r o s s - s e c t i o n of the plasma and when  range  from  p r e s s u r e was  Pa.  p o s i t i o n e d 6 cm along the magnetron a x i s .  conventional  magnetrons  f l o a t i n g p o t e n t i a l stayed constant 1  to  2  Pa,  lowered t o .5 and  respectively. stayed  .25  power requirements of the system went from 27 t o  decreased  the  a  Pressure The  The  has  i n d i c a t e s t h a t the  d i s c h a r g e c u r r e n t over t h i s range. w i t h t h a t o f Ref  and  constant  However,  both  to within  but  are  increased  - 26  error.  ground This  i s also  and  as  and - 42 ion  The  volts in  sharply  .25 Pa t o - 32 the  the  employed.  at about  30  the  volts  currents  indicates that  for  carbon, the i o n f l u x i s independent of p r e s s u r e i n t h i s range. S i m i l a r r e s u l t s have a l s o been noted f o r copper and  silicon . 1 4  E. ION/DEPOSITION FLUX RATIO  1.  Introduction The  purpose of the next s e t of t e s t s was  t o examine the  Experimental Results / 77 ion/deposition determine how and  2.  f l u x r a t i o f o r magnetron 5.  The  g o a l was  t o both maximize the i o n / d e p o s i t i o n f l u x  the e f f e c t i v e d e p o s i t i o n  Deposition  ratio  area.  F l u x Measurements  The d e p o s i t i o n f l u x d u r i n g a s p u t t e r i n g run was Copper was  to  measured.  chosen as a t a r g e t m a t e r i a l as i t had been used i n  the i o n f l u x measurements and had a h i g h s p u t t e r i n g r a t e . d e p o s i t i o n r a t e s were determined by weighing g l a s s before  and  after  Special experiment, mechanically  two  clamp  holders purposes  the  were  designed  i n mind.  The  substrates  expose  the  same area,  i n place,  d i f f e r e n t substrate s i z e s .  eliminating  The h o l d e r was  this  was  avoiding  to such  Secondly, they  the 1/8  for  first  methods as t a p i n g which would leave a r e s i d u e . would  substrates  deposition.  substrate with  The  error  due  to  " t h i c k and  had  a 1 " h o l e m i l l e d i n deep enough t o accommodate the  substrate.  A l i p covered the top of the s u b s t r a t e so t h a t an area of " diameter was  exposed.  45 degrees t o prevent any  The  l i p was  cut back a t an angle of  shadowing e f f e c t s .  The d e p o s i t i o n t e s t went as f o l l o w s .  The g l a s s  substrates  were weighed immediately a f t e r c l e a n i n g on a s c a l e a c c u r a t e 10"  and  h o l d e r were cleaned w i t h i s o p r o p y l a l c o h o l .  The s u b s t r a t e  was  then  any  the  fastened  The  to  contact  the  s u b s t r a t e blown o f f .  areas of the  substrate The  table  substrate  to  table  5  grams.  7/8  and  d e p o s i t i o n time was  dust  on  chosen so t h a t  Experimental R e s u l t s / 78 2.5E1 6 r (N E  y 2.0E16 o CO  \  | 1 .5E1 6 o  2o  ^_  1.0E1 6 -  o % 5.0E1 5 o CL Q>  Q  O.OEO • 4  1  ' 5  '  ' 6  1  1  1  7  1  1  1  1  8  1  1  9  Position (cm)  1  1  1  10  1  1  11  12  13  F i g u r e 5.17 D e p o s i t i o n r a t e s along the a x i s f o r magnetron 5 f o r a d i s c h a r g e c u r r e n t o f 200 mA and a copper t a r g e t . the f i l m s would weigh a t l e a s t 10" grams. T h i s was 3  about t e n minutes a t a d i s c h a r g e  typically  c u r r e n t o f 200 mA.  After  d e p o s i t i o n , the f i l m and s u b s t r a t e were blown f r e e o f dust and weighed immediately. function estimated  of a x i a l  The d e p o s i t i o n f l u x was examined as a  distance.  t o be +/-  The e r r o r o f measurement  1.5 x 10"  4  grams.  The d e p o s i t i o n r a t e s were measured  along  a x i s between 5 and 12 cm i n increments o f 1 cm.  the magnetron The p r e s s u r e  was h e l d constant a t 1 Pa and the d i s c h a r g e c u r r e n t a t 200 At factor.  this  pressure  there  was  mA.  i s not a s i g n i f i c a n t s c a t t e r i n g  T h e r e f o r e we would expect the d e p o s i t i o n r a t e along  the a x i s t o go approximately along the a x i s .  as 1/z  2  where z i s the d i s t a n c e  To t e s t the above model a l e a s t squares f i t  Experimental Results / 79 was  performed  on  deposition rate.  the  logarithms  The  r e s u l t s were  Value o f n i n l / z F i g 5.17  is  n  2.0  of  +/-  the  axial  position  »05  shows the r e s u l t s along w i t h the b e s t f i t l i n e .  data has  been presented  i n u n i t s of atoms/s-cm .  This  2  determined by d i v i d i n g the mass of the f i l m by the area, d e p o s i t i o n time and  3.  Ion/Deposition The  showed  results that  the  magnetron a x i s . along  and  The was  substrate  the atomic mass of copper.  f l u x maximization from ion The  the  small  current  radial  probes,  i s largely  Fig.  focused  i o n / d e p o s i t i o n f l u x r a t i o was  the magnetron a x i s from 5 t o 11 cm.  The  about  5.10, the  determined  ion flux  was  determined by d i v i d i n g the c u r r e n t s t o the s m a l l c e n t r a l probe by  the  area  of the  determination r a t i o along results  probe and  the  charge on  the  ions.  of the d e p o s i t i o n f l u x was d i s c u s s e d above. the magnetron a x i s i s shown i n F i g . 5.18.  show  that  the  ion/deposition  s u b s t r a t e p o s i t i o n s c l o s e r t o the  ratio  increases  The The The for  target.  A l s o o f importance i s the u s e f u l d e p o s i t i o n area f o r h i g h ion/deposition radial  flux ratio.  d i s t r i b u t i o n of the  F i g . 5.19  shows the  ion currents  normalized  f o r magnetron 5 a t  v a r i o u s p o s i t i o n s along the magnetron a x i s .  The r e s u l t s show  t h a t the d i s t r i b u t i o n becomes more focused at p o s i t i o n s c l o s e r t o the t a r g e t . from  the  axis  The r e d u c t i o n i n the i o n / d e p o s i t i o n r a t i o away is  partially  compensated  by  the  reduced  Experimental Results /  3.0  O  I  1  1  1  1  1  1  1  1  1  1  1  r  2.5  < cc X  2.0  O  1.5  O Q. Ld Q  1 .0  ^  0.5 0.0  _i  i  i  6  i i_ 7  _i  i i_  8  9  10  11  12  AXIAL POSITION (cm) F i g u r e 5.18 I o n / D e p o s i t i o n f l u x r a t i o a l o n g t h e a x i s magnetron  1.2 UJ  0  4 cm 7 cm 1 0 cm  O • A  1 .0  0.0  1  for  5.  2  3  4  5  RADIAL POSITION (cm) F i g u r e 5.19 I o n c u r r e n t s v e r s u s  radial position for m a g n e t r o n 5. The i o n c u r r e n t s a r e n o r m a l i z e d for comparison purposes.  80  Experimental Results / 81 deposition  flux.  At  pressures  low  enough  to  s c a t t e r i n g , the d e p o s i t i o n f l u x f o l l o w s approximately relationship ,  where cos8  ratio  of the  d i s t a n c e o f the p o i n t of d e p o s i t i o n from the  centre  2 7  substrate distance  (which of  the  i s on  i s equal  the  substrate  to  magnetron from  the  axis) target.  approximation, the i o n / d e p o s i t i o n r a t i o was  and  prevent a cos 6 2  radial of  the Using  the  axial this  found t o decrease  a t a r a d i a l d i s t a n c e from the c e n t r e o f the s u b s t r a t e o f 2 cm t o 23,  41 and 70% of t h a t a t the c e n t r e  , f o r a substrate at  a d i s t a n c e from the t a r g e t of 4, 7, and 10 cm, r e s p e c t i v e l y .  CHAPTER VI. CONCLUSION  The  objectives  mechanisms  involved  magnetrons manner  of  have  than  been  the  t h e s i s have been a c h i e v e d .  in  ion  investigated  previously  understanding of the  investigations  ion/deposition  a  This  for more  unbalanced quantitative  has  lead  to  an  secondary d i s c h a r g e  in  the  of h i g h i o n f l u x e s a t the  have  ratio  in  studied.  r o l e o f the  f u n n e l i n the p r o d u c t i o n The  production  also  The  shown  how  through placement  to  substrate.  maximize  along  the  the  magnetron  a x i s and the c o n s i d e r a t i o n s necessary t o m a i n t a i n an e f f e c t i v e area of s u b s t r a t e As this  bombardment.  s t a t e d above, the  t h e s i s show t h a t  r e s u l t s presented and  large  currents  to  the  discussed substrate  h i g h l y dependant on the development of a secondary away from the magnetic t u n n e l . the the  ability  of the  ionization  designing both the  This discharge  of  the  i s dependant on  sputtering  above  gas.  unbalanced magnetrons, a t t e n t i o n must be s p a t i a l dimensions of the  When given  secondary b o t t l e and  magnitude of the l o c a l f i e l d maximum (B ) 3  are  discharge  secondary b o t t l e t o t r a p e l e c t r o n s  potential  in  to the  i n order t o a c h i e v e  large ion/deposition flux ratios. Care  must  also  be  taken  with  respect  to  the  target  t h i c k n e s s as t h i s e f f e c t s the t u n n e l , which, i n t u r n , e f f e c t s the secondary d i s c h a r g e . t h e s i s was  The optimum magnetron chosen i n t h i s  c o n f i g u r a t i o n 5 w i t h a 3 mm 82  target.  Configuration  Conclusion 6 w i t h a 8 mm the  t a r g e t produced  substrate,  design.  The  second was  but  had  f i r s t was  two the  /  83  higher o v e r a l l ion currents  at  disadvantages over the greater  previous  power requirements.  The  the f a c t o r t h a t small changes i n the t u n n e l l e a d t o  l a r g e changes i n i o n c u r r e n t s i n d i c a t e d by the d i f f e r e n c e s i n the  discharges  between  magnetrons  5  and  6.  This  causes  problems d u r i n g the s p u t t e r i n g process as the t a r g e t t h i c k n e s s decreases over time.  A system c o u l d be designed t o move the  magnetics d u r i n g  deposition  the  process,  but  at  a  loss  of  simplicity. The i o n / d e p o s i t i o n f l u x r a t i o was  shown t o be dependant on  the a x i a l p o s i t i o n of the s u b s t r a t e w i t h the r a t i o i n c r e a s i n g towards the target  target.  distances  the  However, a t useful  t r a d e o f f e x i s t s between the deposition  areas.  t a r g e t a l s o has  Moving  the  deposition  shorter  substrate  to  area  i s l e s s and  a  ion/deposition the  substrate  ratio  and  further  the disadvantage of r e d u c i n g  the  larger  from  the  deposition  rate. A  possible  simple  method  that  would  allow  larger  d e p o s i t i o n areas c l o s e r t o the t a r g e t i s t o a l t e r the magnetic f i e l d beyond the secondary d i s c h a r g e .  I f the f i e l d l i n e s were  l e s s focused beyond t h i s p o i n t , the i o n c u r r e n t s would be more evenly  distributed radially.  f i e l d l i n e s c o u l d be achieved  The  d e s i r e d a l t e r a t i o n of  the  through the c o r r e c t p o s i t i o n i n g  of a d i s k magnet behind the s u b s t r a t e t o reduce the magnitude of B  2  and  i n c r e a s e the magnitude of B . p  Care would have t o be  Conclusion  /  84  taken both t o a v o i d c r e a t i n g another magnetic b o t t l e , as t h i s would i n c r e a s e the l o c a l i z a t i o n of the i o n c u r r e n t s , and t o avoid magnet  decreasing bottle  electrons.  to  the  trapping  below  that  efficiency which  of  could  the trap  secondary ionizing  REFERENCES 1.  J.A. Thornton and A.S. P e n f o l d , i n "Thin F i l m Processes" (J.L. Vossen and W. Kern) Chap. 2 , Academic Press, New York, 1978.  2.  J.L. Vossen and J . J . Cuomo, i n "Thin F i l m P r o c e s s e s " (J.L. Vossen and W. Kern) Chap. 1 , Academic Press, New York, 1978.  3.  J . G . L i n h a r t , " Plasma P h y s i c s " , N o r t h - H o l l a n d P u b l i s h i n g Co., New York, 1961.  4.  W.Knauer, J . A p p l . Phys. 33,  5.  B. Window and N. S a w i d e s , J . Vac. S c i . Technol. A4, (1986).  6.  J.A.Thornton, Ann.  Rev.  7.  J.E. Sundgren and A4, 307 (1986).  H.T.G. H e n t z e l l ,  8.  N. S a w i d e s , J . Appl. Phys. 5 9 ,  9.  H.R. Kaufman, J . J . Cuomo and J.M.E.Harper, J . Vac. S c i . Technol. 21, 405 (1982).  10.  S. S c h i l l e r , V. H e i s i g and K. Goedicke, T h i n S o l i d F i l m s 40, 327 (1977).  11.  T. Minami, H. Nanto, and S.Takata, A p p l . Phys. L e t t . 41, 985 (1982).  12.  S. O n i s h i , M. Eschwei, and W.C.Wang, A p p l . Phys. L e t t . 38, 419 (1981).  13.  D.B. F r a s e r and H.D. (1977).  Cook, J . Vac. S c i . T e c h n o l . 14,  147  14.  N. S a w i d e s and B. Window, J . Vac. S c i . Technol. A4, (1986).  504  15.  B. Window and K.H. (1989).  183  16.  A.G. Spencer, K. Oka, 38, 857 (1988).  17.  R.P. Vac.  2093  (1962).  Mater. S c i . 7, 239  4133  (1986).  171,  Howsen and R.W.Lewin, Vacuum  Howson, A.G. Spencer, K. Oka, and R.W. S c i . Technol. A7, 1230 (1989). 85  (1977).  J.Vac.Sci.Technol.  Muller, Thin S o l i d Films R.P.  196  Lewin, J .  References / 86 G.L.  Harding, J . Vac. S c i . T e c h n o l . A 8 ,  18.  B.Window and 1277 (1990).  19.  B. Chapman, " Glow Discharge and Sons, New York (1980).  20.  D. Bohm and E.P. Gross, Phys. Rev. 75,  21.  E.S. McDaniel," C o l l i s i o n Phenomina i n I o n i z e d Ch. 13. Wiley, New York, 1964.  22.  W.Knauer, J . A p p l . Phys. 3 3 , 2093  23.  D. Bohm, E.H.S. Burhop, and H.S.W. Massey, i n "The Characteristics of E l e c t r i c Discharges i n Magnetic Fields" (A. G u t h r i e and R.K. Wakerling, e d s . ) , pg. 13. McGraw H i l l , New York 1949.  24.  S.M. Rossenagel and H.R. A 5, 88 (1987).  25.  P. Horowitz, W. H i l l , " The A r t o f E l e c t r o n i c s " , 1007. Cambridge U n i v e r s i t y P r e s s , New York 1989.  26.  L. H o l l a n d and G. Samuel, Vacuum, 3 0 , 267  27.  R. Glang, i n " Handbook o f T h i n F i l m Technology" ( L . I . M a i s s e l and R. Glang), McGraw-Hill, New York 1970.  28.  J.D. Jackson, " C l a s s i c a l E l e c t r o d y n a m i c s " Chap. 5, John Wiley and Sons , New York 1975.  Processes", John 1851  Wiley  (1949). Gases",  (1962).  Kaufman, J . Vac. S c i . T e c h n o l . pg.  (1980).  APPENDIX  F l u x from a magnet  face  Though the c a l c u l a t i o n s f o r a magnetic f i e l d p o i n t i n space i s q u i t e d i f f i c u l t ,  at a given  a much s i m p l e r t a s k i s t o  determine the net f l u x l e a v i n g the f a c e o f a magnet. T h i s can be shown by c o n s i d e r i n g a c y l i n d r i c a l  magnet w i t h  the same  c o o r d i n a t e system as F i g . 3.1 w i t h a r a d i u s , R, and a depth, b. For a magnet with a magnetization the v e c t o r p o t e n t i a l i s g i v e n b y  M(x')  the s o l u t i o n t o  28  assuming t h a t M i s constant throughout the volume then VxM(x')  = 0  therefore  As t h e magnet i s magnetized along i t s z a x i s we have t h a t M z x z= 0 and M zxr~M 0  87  /88  Therefore  AU)-rrr^- rdz'dQB n  J-ilx-x1  Jo  and  i t can be seen by symmetry t h a t A  e  i s a f u n c t i o n of r and  z only. Now  consider  the  flux  through  one  of  the  faces  of  the  magnet <j) - j B-nds - 271 j B R  Now,  as A  f  = 0 we  value  numerically  of  58  have  A  f o r 8.  e  ^  is The  , 6\r'  r'dr'  ° 27rA> (a,  analytic  in  z  flux  magnet i s a l s o q u i t e simple see  dr  i  (t>=27r./ —, •'o r '  The  r'di'  i n c y l i n d r i c a l c o o r d i n a t e s we have t h a t  z  And  ( r , 0) 7  Z  from the  and  surface  Q  can  be  solved  of an  annular  t o s o l v e f o r . From above we  that ^=2%A (R,  0)  0) -2UAQ(R  OI  0)  can  

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0074522/manifest

Comment

Related Items