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UBC Theses and Dissertations

Fabrication process and characteristics of a silicon strip detector Mills, David J. 1985-12-31

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FABRICATION  PROCESS AND  CHARACTERISTICS  OF A SILICON STRIP DETECTOR by DAVID J .  MILLS  B . A . S c , U n i v e r s i t y of B r i t i s h  Columbia,  1983  THESIS SUBMITTED IN PARTIAL FULFILLMENT OF REQUIREMENTS FOR  THE DEGREE OF  Applied  MASTER  OF SCIENCE v  in THE FACULTY OF GRADUATE Department  We  accept to  STUDIES  of E n g i n e e r i n g  this  thesis  the r e q u i r e d  as  Physics  conforming  standard  THE UNIVERSITY OF BRITISH COLUMBIA April  1985  © David John M i l l s  1985  THE  In p r e s e n t i n g  t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f the  requirements f o r an advanced degree a t the U n i v e r s i t y o f B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make it  f r e e l y a v a i l a b l e f o r reference  and study.  I further  agree t h a t p e r m i s s i o n f o r e x t e n s i v e copying o f t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by t h e head o f my department o r by h i s o r h e r r e p r e s e n t a t i v e s .  It is  understood t h a t copying o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l gain  s h a l l n o t be allowed without my w r i t t e n  permission.  Department o f  i ^ ^ g j u  ^r\TilAr^  The U n i v e r s i t y o f B r i t i s h Columbia 1956 Main M a l l Vancouver, Canada V6T 1Y3 ^te  DE-6 (3/81)  Apr]/  - X f  1/  (y/  ABSTRACT  The state  detectors  theory the  current  A  PIN d i o d e  uses  physics  state detectors  of semiconductor  are b r i e f l y  i s discussed  discussed. with  process  sensitive solid  for  silicon  state detectors  surface  prototype  surface  barrier  and t e s t e d a t UBC and TRIUMF  device active  has area  1  mm  o f 40 mm  position  has been d e v e l o p e d a t  The  expected  rate c a p a b i l i t y  2  detector  measured  efficiency  detector using  resolution  i n diameter  mg/cm .  ratio.  barrier  process  i s included.  A built  The  e m p h a s i s on  UBC b a s e d on t h e work o f J.B.A. E n g l a n d . A f a b r i c a t i o n recipe  solid  detector.  fabrication  position  possible  in nuclear  of s o l i d  silicon  and  process.  i n one d i r e c t i o n , thickness  f o r 50 MeV p i o n s  i s i n excess  i s limited  this  and a mass  efficiency  s y s t e m has been  i f 1 MHz  by a m a r g i n a l  of  The an 55  i s 70% and  per s t r i p .  The  signal-to-noise  TABLE OF CONTENTS  CHAPTER What  I : INTRODUCTION is a solid  General  1  state detector?  1  p r o p e r t i e s o f SS d e t e c t o r s  Motivation CHAPTER  ..  for detector  development  3 a t TRIUMF  4  I I : PRINCIPLES OF OPERATION  B a s i c band t h e o r y charge generation  of s e m i c o n d u c t o r s and 8  B u l k t y p e SS d e t e c t o r s , semiconductors Diode d e t e c t o r s ,  Energy  r e s i s t i v i t y of 11  electrical  Charge c o l l e c t i o n  Depletion  Position  14 20  leakage c u r r e n t  ..23  r a d i a t i o n damage  depth, energy  Transmission  characteristics  time  resolution, noise,  Leakage c u r r e n t ,  8  26  resolution  27  detectors  28  resolution  ...29  CHAPTER I I I : FABRICATION OF DEVICES Ion  Implanted  Surface  SS d e t e c t o r s  barrier  31  SS d e t e c t o r s  Preliminary e l e c t r i c a l barrier detectors CHAPTER  31  characteristics  ....34 of s u r f a c e  IV: SOLID STATE DETECTOR SYSTEM TEST  Preamplifier  electronics  39 43 43  iv Alpha Beta  source source  Observed  tests,  46 50  of system  53  design  53  Beam t e s t ,  position  Beam t e s t ,  noise  Beam t e s t ,  bias voltage  Timing  asymmetry  tests  noise  Beam t e s t  detector  resolution  and e f f i c i e n c y  o f SS d e t e c t o r  and e f f i c i e n c y  signals  55 60 67 70  CHAPTER V: SUMMARY AND CONCLUSION  72  Noise,  improvements  72  Future  considerations  74  BIBLIOGRAPHY  75  APPENDICES: A p p e n d i x A: M o d i f i e d E n g l a n d surface barrier detectors  process f o r ....76  LIST  Table  2.1  OF  TABLES  Charge c a r r i e r mobilities of s e m i c o n d u c t o r s  vi  L I S T OF F I G U R E S  Figure  1.1  Generic  solid  state detector  Figure  1.2  T R I U M F M13  Figure  1.3  Photographs  Figure  2.1  Charge  Figure  2.2  Charge c a r r i e r  pion  2  beamline  of prototype  generation  5 7  detector  i n SS d e t e c t o r  10  concentration i n  semiconductors Figure  2.3  PIN diode  Figure  2.4  Band d i a g r a m s  Figure  2.5  Electrical biased  13 .15 o f pn j u n c t i o n  characteristics  16  of a  reverse  pn j u n c t i o n  Figure  3.1  Implantation  Figure  3.2  Cross  18  fabrication  technique  section of the surface  32  barrier  detector  35  Figure  3.3  Cross  s e c t i o n of the detector  Figure  3.4  Leakage c u r r e n t  Figure  4.1  Photograph  Figure  4.2  Figure  4.3  Figure  4.4  C i r c u i t diagram of d e t e c t o r p r e a m p l i f i e r s and b i a s v o l t a g e Response of d e t e c t o r t o alpha p a r t i c l e s Asymmetry of response of d e t e c t o r to alpha  particles of detector  4.5  Response  Figure  4.6  Noise  Figure  4.7  Data a c q u i s i t i o n beam t e s t  38  of prototype  of detector  Figure  mount  41  preamplifiers  ....44  45 47 48  to beta  particles  in detector/preamplifiers  ..51 52  electronics for 54  vii Figure  4.8  Beam t e s t  Figure  4.9  S c a t t e r p l o t of d e t e c t o r w i r e chamber p o s i t i o n  position  Scatterplot  position  Figure  4.10  apparatus  w i r e chamber  56 57  of d e t e c t o r position,  noise  versus  only  Figure  4.11  Position  Figure  4.12  Beam p r o f i l e a s seen w i t h  Figure  4.13  M u l t i p l i c i t y of d e t e c t o r  Figure  4.14  Figure  4.T5  E f f i c i e n c y a n d n o i s e of SS d e t e c t o r and w i t h o u t n o i s e r e j e c t i o n D i s t r i b u t i o n o f muon l a b a n g l e f o r p i o n decay  Figure Figure Figure Figure  4.16  resolution  versus  58  of d e t e c t o r  59  SS d e t e c t o r  ...61  events  Histograms of p a r t i c l e angles beam t e s t  63 with 64 65  i n the 66  4.17a G r a p h i c a l summary of e f f i c i e n c y and n o i s e o f t h e SS d e t e c t o r  68  4.17b G r a p h i c a l summary o f e f f i c i e n c y and noise continued  69  4.18  Time s p e c t r u m s o f s i g n a l s detector  from SS 71  ACKNOWLEDGEMENTS  I would use  of  like  the  Engineering  to express solid  department  my t h a n k s t o . D r .  state  laboratory  state fabrication  I  am i n d e b t e d  A. Amaudruz experimental PISCAT g r o u p Thanks Dr.  R.R.  guidance  Many  f o r t i m e and h e l p  during  t o thank  Dr.  t e c h n i c a l advice i n  t o J . C r e s w e l l , D. Maas, G. S h e f f e r and P.  techniques.  Johnson  fortheir  Electrical  techniques.  f o r technical advice  are  the  a t UBC. I would a l s o l i k e  P. J a n e g a a n d D r . J.B.A. E n g l a n d solid  in  L . Young f o r t h e  due and  on  electronics  and  nuclear  t h a n k s t o P. Amaudruz and t h e i n t h e beam  experiments.  t o my s u p e r v i s o r D r . K a r l Erdman a n d t o Dr.  this project.  D.  Gill  f o r encouragement  and  CHAPTER I  INTRODUCTION The  use o f s o l i d  state detectors  in  nuclear  i n c r e a s i n g . The d e v e l o p m e n t o f f a b r i c a t i o n reduced What  their  c o s t and improved  is a solid The  state  their  state) detector  crystal  with  internal  external  voltage  X-ray  is  generates  the i n t e r n a l  as  a current pulse SS  types.  electric  detectors In b u l k  i s a s l a b of field  semiconducting  generated  by an  charged  particle  i t s passage  through  the  crystal  w h i c h a r e swept o u t o f  the  crystal  field  and a r e d e t e c t e d  or  electronically  ( F i g u r e 1.1). can  be c l a s s i f i e d  detectors  the  semiconductor  i s very  compensation  techniques.  contacts  the  to  both  i t . A  when  charge c a r r i e r s  by  has  quality.  electric  applied across  detected  technology  is  detector?  SS ( s o l i d an  physics  intrinsic  low due t o h i g h  normally  as e i t h e r bulk  One  only  conductivity  crystal needs  insulating  or  diode  of  the  p u r i t y or charge to  crystal  attach  ohmic  to produce a  detector. The bulk  diode  detector  has l e s s  stringent restrictions  p r o p e r t i e s of the semiconducting  depletion active  zone c r e a t e d  in a reverse  region. This active  region  material  and  on t h e  uses  the  b i a s e d pn j u n c t i o n a s i t s can  extend  partially  or  2  FIGURE 1 . 1  BIAS  Schematic  of  a  semiconductor  VOLTAGE  charged  particle  detector.  3  completely General  through  the c r y s t a l  properties  Solid  state  particles,  energy  combination  of  detectors  o f SS  detectors  detectors  can  resolution, the  make  slab.  three.  them  be  designed  postition  resolution  The i n t r i n s i c  versatile  for timing  devices  of -  or  some  properties of  these  with  some  unique  propert ies.  SS  detectors  internal  designed  electric  fields  nanoseconds with  pulse  timing  and high  of events  Position patterning  the  (REF  built  stopped  particles  charge  detector,  SS  times  and  of nanoseconds.  rate a p p l i c a t i o n s are thus in  SS  detectors  collecting  is  of  Accurate possible.  achieved  electrodes. With  techniques,  high  i n the order  by  standard  S i detectors  5 um r e s o l u t i o n f o r m i n i m u m i o n i z i n g  detectors  proportional  (REF  rise  of tens  photolithographic  with  capacitance  have  particles  6). SS  The  widths  charge  small  have p u l s e  resolution  semiconductor been  for  can  pulse  produced  t o the energy  and  detectors.  X-rays,  used  or the energy  may  lost  this  i s commonly  used  their  determine  the energy of  l o s s of t r a n s m i t t e d by  the  particle  i n the active  has been  A single detector  and measure  to  b e m e a s u r e d down  4). Historically,  detectors  be  t o stop energy.  i s  region  t o a few p e r c e n t t h e m o s t common  or stack low  of t o t a l l y  energy  particles. directly of  the  accuracy use  for  depleted  particles  or  The solid  energy  state  fluctuation This  detector  semiconductor  the  life  current  development  greater  to l e v e l s  area  one  considers require  containment  state  detectors  future  even  detector.  other  bulky  light  Motivation  need  may  built  high was  be  rate the  primary  TRIUMF. The TRIUMF M13 p i o n of  2X10 /S. 6  A high  of  the  significant  in  This  sensitive  and  of  avoided  relatively  or  photomultipliers  preamplifiers, amplifiers wafer  a r e used e x t e n s i v e l y  good b e h a v i o r  when  timing  position sensitive  with  of  diameter  i s l e s s o f a drawback  pipes  development  used.  reduction  5 cm  2  position  capability  of the o r i g i n a l  (REF 6 ) .  2  on t h e same s e m i c o n d u c t o r  due t o t h e i r  particles.  techniques  (=25 mg/cm ).  SS d e t e c t o r s  of  the  l e s s than  large arrays  f o r detector  detectors  excess  been  systems. At present,  At present  physics  The  that  this  readouts being  energy  thick  t h e random  The most  a s low a s 40 nA/cm  are t y p i c a l l y  a  by  by t h e i n c r e a s e  has  in  t o l e a k a g e c u r r e n t , and  value.  and l a r g e mass t h i c k n e s s  detectors gas  i s limited  100 m  than  small  absence  and on t h e f a b r i c a t i o n  detectors  These d e t e c t o r s and  i n the  t o some c r i t i c a l  i n these  current  primarily  can a l s o c o n t r i b u t e  current  detectable  depends on t h e i n t e g r i t y  material  damage  limited  flowing  o f an SS d e t e c t o r  leakage  leakage  is  of c u r r e n t  leakage  Radiation  r e s o l u t i o n o r minimum e n e r g y  in high  or  solid  but  in  o r CCD as  the  i n low  vacuum.  a t TRIUMF  of  position  motivation  SS  f o r b u i l d i n g them a t  b e a m l i n e c a n have rate detector  sensitive  p i  +  fluxes  c a n be u s e d  in  in this  5  FIGURE  1.2  M13 p i o n beam l i n e a t T R I U M F . B1 a n d B2 a r e d i p o l e b e n d i n g m a g n e t s ; F l a n d F 2 a r e t h e f o c u s l o c a t i o n s o f t h e momentum selection slits.  channel in of  as a beam p r o f i l e  scattering the pion  monitor  for diagnostics  experiments. Currently  beam  i s selected  t h e momentum  by a p a i r  of  f o c u s e s downstream of a b e n d i n g magnet A SS d e t e c t o r tag as  the  located  position  i t traverses  increase  and t h e r e f o r e  pion  target  the  resolution  A been  position built  experimental silicon  surface  millimeter  without  in  at  barrier one  at  can then  be  degrading state  particle  opened  the  to  momentum  detector  monitor  to  a t the  t o improve  of t h e s p e c t r o m e t e r .  tested  group  used  t h e momentum o f e a c h  c a n be u s e d a s a p o s i t i o n  sensitive,  and  located  f o c u s e s c a n be  I n a s i m i l a r manner, a s o l i d  scattering energy  flux  slits  resolution  ( F 1 , F2 i n F i g u r e 1.2).  t h e c h a n n e l . The s l i t s  the  resolution.  a t one o f t h e s e  or as a t o o l  silicon,  by  the  TRIUMF.  PISCAT The  techniques.  direction  d i a m e t e r a n d i s 230 jum t h i c k  solid  and  state  d e t e c t o r has  (pion  device  was  scattering) made  I t has a r e s o l u t i o n an a c t i v e  area  o f one  o f 4 cm i n  (55 mg/cm ), ( F i g u r e 1.3). 2  using  Surface barrier, position m a n u f a c t u r e d a t UBC. The are v i s i b l e .  sensitive, solid state detector p r e - a m p l i f i e r readout e l e c t r o n i c s  CHAPTER I I  PRINCIPLES OF OPERATION Basic  band  t h e o r y o f s e m i c o n d u c t o r s and c h a r g e g e n e r a t i o n  A semiconductor energy  states  normally band.  for  Similarly, full  the  states  temperature  states  electrons.  w i t h a gap i n t h e The  empty and a r e c o l l e c t i v e l y  normally zero  is a crystal  the energy  below  without  temperatures, distribution  the  no  band  are  of e l e c t r o n s  or holes  E  collection  any  of  crystal  Pauli  energy  are p'  conduction  i n the lowest  the Fermi  energy,  the  the  electrons  the  In  lying  Fermi  above t h e gap a r e  as  is  violating  At zero temperature above w h i c h  known  t h e band gap.  electrons  possible  principle.  valence  states  available  at  energy  exclusion  i s d e f i n e d as  seen.  defines  At  non-zero  the  thermal  (REF 8 ) :  .-(E -E /kT) c  F  n = N e c -(E -E /KT) p  v  p = N e ^ v  2.1  Equations where n and p a r e t h e r e s p e c t i v e  densities  holes,  i n t h e c o n d u c t i o n band, E  E  c  i s the e l e c t r o n  the h o l e energy of  states  for  energy  i n t h e v a l e n c e band, N  c  of  and N  v  electrons  are  t h e c o n d u c t i o n and v a l e n c e bands  and v  is  densities  respectively  and  kT  i s the  vacancies positive the an  temperature  in  the  charged  electron  crystal  lattice.  the  Insulators  usually  In  a  solid  semiconducting non-conducting charge  carriers).  crystal  valence  has  and  electrons  an a  This  phonon e x c i t a t i o n , electrons  on  the  with a  larger  band  the  full  motion  like  valence  an  empty  more  or  in  of  sites  than by  the  band  (no  (no  gap.  of  hole the  charge crystal  states  quickly  The  electron  (holes)  scattering  electron-hole  the  insulator.  energy  configuration  r a d i a t i v e decay  carriers  volume  band  band  available  behind  the  gap.  p a r t i c l e passes through the  in  the  active  acts  state  characterized of  of have  "lighter"  centre  excited  (generating  holes  100%  or  like  mass  and  and  empty c o n d u c t i o n  into  band, l e a v i n g  band.  10%  the  normally  behave  charge  "heavier"  detector  When a c h a r g e d  scatters  conduction  to  state  carriers)  between be  same but  state  of  electron  the  electrons  semiconductors are  lying close the  to  i t s d i r e c t i o n of  masses  are  h o l e s can  Intrinsic  are  on  Effective  mass and  energy  band and  c r y s t a l w h i c h depends  p a r t i c l e and  semiconductors  Fermi  valence  ( e f f e c t i v e mass). Both  by  electrons.  full  u n i t s . Holes are  p a r t i c l e s w i t h a mass c l o s e  occupied  it  almost  e f f e c t i v e mass i n t h e  electron  in energy  in  the  in  the  decays  from  pairs)  by  valence until  a  -1 2 quasi-stable state holes  is  state  is  reached  characterized  in  the  conduction  carriers  are  free  the  detector  and  by  form t h e  an  and  to d r i f t  (10  s).  equal valence  i n the  detected  This  number of bands.  longer electrons These  internal electric current  pulse  lived and  charge field  (Figure  of  2.1).  10  FIGURE 2 . 1  I  L_.  L_.  !<£>  I  (  I  1_.  I"  CONDUCTION I BAND | BAND GAP  I  Q  L.  ,  i>-  I  r-  I  1°"  A  VALENCE BAND  >CD  cr. UJ LU  EQUILIBRIUM  AT TIME OF IONIZATION  Schematic of charge g e n e r a t i o n of a s o l i d s t a t e d e t e c t o r .  process  1 ps AFTER IONIZATION  i n the  active  region  The s i z e energy and  loss,  of t h i s  current  pulse,  Q,  i s proportional  AE, of t h e d e t e c t e d p a r t i c l e  t o the  i n the a c t i v e  region  i s g i v e n by Q = qKAE/E • gap Equation  where Q i s t h e c h a r g e or  electrons),  E  generated  i n the d e t e c t o r  (either  holes  i s t h e band g a p o f t h e s e m i c o n d u c t o r gap  3  2.2  (1.12  r  eV f o r S i ) and q i s t h e e l e c t r o n i c  charge. K i s a factor  less  than  energy  than  one  that  ionization, Si  as  about  eV  is  hole pair  30  for  eV  the average  per  ionization collection  multiplication  also  occurs  however, in  and  often  semiconductor  Bulk  field.  causes  SS  semiconductor. electrodes detector strength  An  external an  made  of  from  controlled,  so i t i s n o t u s e d  high  V,  resistivity  applied  electric  For a s l a b of t h i c k n e s s  i s u n i f o r m l y V/d.  a high  semiconductors  voltage,  internal  with  i s not e a s i l y  detectors.  generates slab.  semiconductors  resistivity  require  charge  charged p a r t i c l e  are  chambers  an  Avalanche  breakdown,  detectors  to produce  in  charge  wires.  effect  1/3  use a v a l a n c h e  total  t y p e SS d e t e c t o r s ,  Bulk  in  This  required  and o f t e n  other  K i s about  ionization  near  electric  energy  (REF 7 ) . Gas  multiplication  internal  losses  f o r example phonon e x c i t a t i o n .  3.2  electron  accounts  field  to contact in  d, t h e e l e c t r i c  the field  One  limitation  resistivity  of  bulk  of t h e c r y s t a l  carriers.  The  leakage  calculated  from  equilibrium  the  due  to  current  is  the  finite  thermally  excited  charge  of  semiconductor carrier  detectors  bulk  detectors  properties.  concentration  i s given  can  be  In  thermal  by  Equations  2.1 o r  -E np = n ^  - e  2  gap  AT Equation  where  n  and  p  respectively, ^  in  the  the semiconductor energy  units.  density  of  detector  A  electrons  carrier  proportionality is  i s shown  leakage  of  and  omitted.  in (Figure  current  constant The  2.2)  dependent  intrinsic  J  n  E gap  temperature  f o r Ge, S i ,  per u n i t area,  holes  concentration, '  band gap, kT i s t h e a b s o l u t e  states  concentration electron  density  n. i s t h e i n t r i n s i c i  J  is  are  carrier  GaAs.  The  , i n an i d e a l  bulk  =  n  qn^M Equation  q  i s the e l e c t r i c  concentration, electron 1kV/cm GaAs  mobility.  bulk  For  field,  detectors  respectively.  charge,  E i s the i n t e r n a l  electric  behavior  on  (n=p=n^) i s (REF 8 ) : J  where  2.3  Of t h e s e  a t room  n^=n  i s the e l e c t r o n  electric  example,  field  leakage c u r r e n t s  are  A/cm ,  three  temperature.  2  only  carrier  and u  is  the  a t room t e m p e r a t u r e w i t h  the best 14  2.4  3  GaAs  for  mA/cm  2  has  an  Ge,  and 2  a  Si,  uh/cm  acceptable  2  I n t r i n s i c charge c a r r i e r as a f u n c t i o n of i n v e r s e  c o n c e n t r a t i o n of Ge, S i , and GaAs t e m p e r a t u r e ( a f t e r Sze R e f . 8 ) .  In  a non-ideal  produced contact  by  ohmic.  contribute  detector,  the i n j e c t i o n  electrodes  contacts  bulk  i f s p e c i a l care Unwanted  sites  d i s c u s s i o n of  section  on d i o d e d e t e c t o r s .  commercially  detectors gap  donor as  caused  Further  of  of c h a r g e s  charge c a r r i e r s  recombination  feasable.  semiconductors  current  can  i n t o the c r y s t a l  i s not taken or  can  to  acceptor  mid-band  current  Recent  included  improvements  semiconductors Bulk d e t e c t o r s  and  faults. i n the  i n the q u a l i t y  are  making  made from  s u c h a s GaAs o r GdS may be  the  i m p u r i t i e s can generation  is  be  by t h e  make  by i m p u r i t i e s o r c r y s t a l  leakage  available  more  leakage  large  common  bulk band  i n the  future.  Diode d e t e c t o r s '  In d i o d e reverse  biased  active  volume  electrical characteristics  t y p e SS d e t e c t o r s , pn j u n c t i o n  that  f o r charged  i t i s the d e p l e t i o n provides  particle  o f a l l j u n c t i o n SS d e t e c t o r s  the  diode  considered Let region be  (Figure  here although us  consider  and the l i g h t l y  made by d i f f u s i n g  such as boron surface fewer  2 . 3 ) . The the p p~n* +  the  barrier.  In  +  site  diode  +  will  by be  of t h e h i g h l y doped p This  pn  junction  a c l a s s I I I dopant  than  semiconductor, in  intrinsic  +  can  element  o r by t h e c o n s t r u c t i o n  a p t y p e doped  e l e c t r o n s per l a t t i c e  -  approximated  i s similar.  doped n~ r e g i o n .  i n t o an n" s u b s t r a t e  are p n n  interface  or i m p l a n t i n g  semi-insulating  d e t e c t i o n . The e l e c t r i c a l  properties PIN  the  zone o f a  of a  there are material  FIGURE  2.3  Xo  Schematic  of PIN  diode  and  definition  of c o o r d i n a t e  X  x.  16  F I G U R E  2.4a  M O B I L E  qVo I O N I Z E D  E L E C T R O N S @ © S> I O N I Z E D  ACC_EPTOR_S_ITES  6 § 5 e 9 g g ) e e e^5>5> ® Q ~ + f++t + + +  D O N O R  ®  ©  S I T E S  € Ef  M O B I L E H O L E S D E P L E T I O N ! Z O N E  J  F I G U R E  2.4b  Band diagrams f o r pn j u n c t i o n w i t h (a) no e x t e r n a l a p p l i e d v o l t a g e , (b) an a p p l i e d v o l t a g e of V . E and Ev a r e the e n e r g i e s of the bottom of t h e c o n d u c t i o n band and t h e t o p of the v a l e n c e band r e s p e c t i v e l y ; E f i s t h e Fermi energy and q i s the e l e c t r o n i c c h a r g e . a  c  and  the Fermi  toward is  level  i s consequently  shifted  downward i n e n e r g y  t h e b o t t o m o f t h e band gap. S i m i l a r l y t h e  shifted  upward  toward  Fermi  level  t h e t o p of t h e band gap i n an n t y p e  semiconductor. In  the  absence  redistribution constant of  of  throughout  the  local  valence  charge  junction barrier holes  and  2.4).  junction  an  and In  totally  n"  or  density  that  the  than  equilibrium  voltage  to the n  to  energy  is  levels of the the  depletion  prevent  a  depleted  across  the  pn  zone  diffusion  i n t o the p region  V  is  (reverse  0  diode, +  of  i n the  is  of +  across  bias), free  (Figure  depletion  zone;  2 . 4 ) . In  zone  extends  In t h e a p p r o x i m a t i o n t h e d i o d e has a much  or n  +  regions  totally  carriers,  one c a n c a l c u l a t e t h e d e p l e t i o n  electric  field  and  depleted width  the  charges  a larger depletion  the  region.  region  zone  applied  proportionately  e i t h e r the p  depletion  7, F i g u r e 2 . 5 ) .  level  a region  change  or e l e c t r o n s  PIN  intrinsic  dopant  thus  enough  increases  depleted  the c r y s t a l  is  bands a r e a f u n c t i o n  t h e j u n c t i o n and l e a v e  b a r r i e r height  leaves  Fermi  t h e j u n c t i o n . The  t h e same s i g n a s V  move away from  This  the  there  gradients.  external  with  field,  that  conduction  i s p r e c i s e l y large  When  the  near  into the n region  across  such  distribution  (Figure  external  the c r y s t a l .  large concentration  the  any  charges  free charge c a r r i e r s  of  a  of  shape as a f u n c t i o n o f a p p l i e d v o l t a g e  lower  assuming  of  and  that  charge internal V  (REF  FIGURE  2.5  CHARGE DENSITY  ELECTRIC FIELD STRENGTH  ELECTRIC POTENTIAL  X  FULLY DEPLETED  X  PARTIALLY DEPLETED  Q u a l i t a t i v e c h a r g e d e n s i t y , e l e c t r i c f i e l d and p o t e n t i a l a s a f u n c t i o n o f p o s i t i o n i n a r e v e r s e b i a s e d PIN d i o d e . C h a r g e d e n s i t y i s p r o p o r t i o n a l t o t h e c o n c e n t r a t i o n o f uncompensated i o n i z e d dopant i o n s .  For  an  depletion  SS  w i d t h , W, W  V  voltage, constant ions  0  V  a  a  i s the  of  s  is  and q  fully  depleted,  the  Equation  2.5  by (REF 7)  n  p o t e n t i a l with  voltage,  the . semiconductor,  field  not  in depletion  applied  i n t h e n~ r e g i o n  electric in  i s given  i s the b u i l t  0  that  = 2(V +V )e /qp  2  where  detector  is  p  n  the  e s  is  no a p p l i e d  the  dielectric  i s the d e n s i t y electronic  of dopant  charge.  i s c a l c u l a t e d by i n t e g r a t i n g t h e c h a r g e  the d e p l e t i o n E(x)  zone and i s t h u s  = (W-x)p /e n  linear  The  density  (REF 8 ) :  0 < x < W  s  = 0  elsewhere Equations  where x i s d e f i n e d For  a totally  at  the width,  is  still  diode,  in Figure depleted  2.3. diode  0  with  t h e same s l o p e  but now h a s maximum and  dependent  the d e p l e t i o n  x , of the i n t r i n s i c  linear  on t h e a p p l i e d  2.5  voltage  region.  width  The e l e c t r i c  as i n a p a r t i a l l y  minimum  i s fixed  values  (Figure 2.5).  field depleted  (E , max  E . ) min  AE  = E  E(x)  -E  max  =  =  min  qp  f l  x /* 0  s  (x -x)AE/x +E 0  0<x<x  0  = 0 V  a +  V  0  =  o  elsewhere x (E 0  m i n +  AE/2)  Equations The  electric  potential  integrating across  the  a t any p o i n t  electric  t h e whole c r y s t a l  field.  i n the c r y s t a l The  2.7  i s found  potential  by  difference  i s the a p p l i e d v o l t a g e , V  , plus the a  built-in diodes  potential, are  (active  (Figure  0  convenient  region)  frequency  V  and  2.5).  Totally  d e t e c t o r s because capacitance  capacitance,  C,  of  width  W i s t h e same a s a p a r a l l e l  width  (REF 8)  are  the  depleted  the d e p l e t i o n  constants.  PIN d i o d e  The  PIN width high  with d e p l e t i o n  p l a t e c a p a c i t o r of the  same  C = Ae /W s  Equation where A i s t h e a r e a Charge c o l l e c t i o n  The the of  signal  drift  time  2.8  of the diode.  time  response  time  i n a SS d e t e c t o r  of charge c a r r i e r s  i s d e p e n d e n t on  a n d on t h e RC t i m e  the d e t e c t o r / p r e a m p l i f i e r system.  constant  The  drift  semiconductor crystal  velocity,  v,  i s proportional  of  charge  to the e l e c t r i c  carriers field,  E,  in  i n the  (REF 8 ) .  v  =  ME  Equation (REF  8) where  electrons  i s  temperature, Carrier are  u i s the  mobilities  shown  carrier  higher  than  doping  i n Table  Table  2.1  mobility.  that  for  concentration for lightly  2.1  f o r Ge,  Carrier  The  holes  and  for  and v a r i e s  with  semiconductor  doped s e m i c o n d u c t o r s  S i and  mobilities  a t 300  k  1 900  450  400  Electrons  3900  1 500  8500  three V/cm  semiconductors a t a v a l u e near  detector  of t h i c k n e s s  noted start 10  7  that  the d r i f t  to saturate  cm/s  K  2  Holes  be  a t 300  (cm /Vs) GaAs  also  type.  GaAs.  Si  should  2.9  mobility  Ge  It  a  velocities  above  (REF 8 ) . F o r a  d, t h e l o n g e s t d r i f t  fields fully  time  i n these of  3000  d e p l e t e d SS  i s g i v e n by:  t  = / dx/V(x) =  / dx/ E(x)  d  (d/MAE)In(E  d  M  /E  •  max' m i n  )  Equat i o n 2.10a where E  _ . E . , AE a r e ma x mln m  m  partially field  depleted  9  =  Q  detector  in  Equations  2.7.  For  a  . i s zero but, as the e l e c t r i c min ' 90% of t h e charge i s c o l l e c t e d i n  i s linear,  t  defined  <.9W/ME  m a x  E  )ln<10) Equat i o n 2.10b  where  W  i s  collection  the  depletion  width.  In  a  bulk  detector the  time i s = d/ME  t  Equat i o n 2.10c where E i s V/d, t h e u n i f o r m 200  micron  S i detector  collection  time would t  = t  0 0  electric  similar  field.  For a hypothetical  t o t h e one b u i l t  a t TRIUMF, t h e  be  l n ( E / E / • ,) max' ( m i n ) Equation  where  t  holes.  0  = 4 ns f o r e l e c t r o n s and t  The c a p a c i t a n c e  This  detector  and  operated  times  made w i t h with  on t h e o r d e r  0  = 13 n s  f o r such a detector small  area  a large bias  the  slower  i s about  50 p F / c m .  fast  electronics  strips, voltage  for  2.1Od  will  of nano-seconds and pulse  have  2  pulse.rise  separation  down  to  30 ns  The very  , depending  efficiency  high  as  on e l e c t r o n i c s r e s p o n s e  f o r charge c o l l e c t i o n  the  carrier  zone. C a r r i e r l i f e t i m e s high  resistivity  carrier  recombination,  still  long  Energy  has a l r e a d y  detector  active  is  region  minimum  but  system. Noise charge  to c o l l e c t i o n  been  The  stopped mono-energetic associated required  with  it  t o produce  pulse  a  intrinsic  distribution  i n terms  milliseconds  radiative  in  electron  i n t h e d e p l e t i o n zone a r e  a charge c o l l e c t e d  t o the energy d e p o s i t e d  The  energy  is  i n SS d e t e c t o r s  noise  i n the d e p l e t i o n  current  stated that  detectable,  by  is  time.  leakage  proportional  generated  background  ideal  lifetimes  of the d e v i c e .  energy  of  detectors  a t room t e m p e r a t u r e . GaAs has s h o r t e r  resolution, noise,  It SS  compared  i s long  M S ) due t o a l l o w e d  (-10  hole  i n SS  a r e on t h e o r d e r  silicon  lifetimes  lifetime  time.  resolution,  limited  is  due  mono-energetic  the  to the d e t e c t o r / a m p l i f i e r  the  i n the  variation  particle  a  i n the or  by t h e n o i s e  to  by  and  in the  system.  i n t h e amount o f c h a r g e g e n e r a t e d by a particle dependent  has on  a  statistical  the  an e l e c t r o n - h o l e p a i r . of energy  i s (REF 7 ) :  average The  variance  energy,  width  of  £, the  W  =  2.96(HE)  1 / 2  Equation where E  of  the  (3.2  eV  statistics  is negligible  for  error  m e a s u r i n g a 6 MeV  small  is  i s the size  in  only  energy  of  11  KeV  scintillators electron  (30  statistical  The mostly  £  (REF  larger  to  500  eV),  noise  noise.and  Shot n o i s e , due to  noise  i s (REF 2  n  >  leakage  particle  The with  proportional  effective and  in a reverse biased  <i  Both these  2  n  >  chambers  have  or  detected larger  thermal  is  due  noise. carrier  current,  charge,  I . s  The  is  directly  mean s q u a r e  shot  Equation  2.12  8)  = 2qBI ^ s  frequency  Thermal n o i s e c o n d u c t a n c e , G,  a Si detector  junction  N  where B i s t h e  to  statistical  e n e r g y per  consequently  the  resolution.  to f i n i t e  proportional  <i  Gas  Because of  u n c e r t a i n t y due  detectors.  alpha  a  intrinsic  Si) this  SS  7).  e r r o r s i n energy  current  for  have eV  to shot  incident particle.  2.11  of  b a n d w i d t h of  interest.  i s p r o p ' o r t i o n a l t o t e m p e r a t u r e and the d e v i c e  (REF  to  the  Equation  2.13  8):  = 4kTBG  n o i s e mechanisms have a u n i f o r m  or w h i t e  frequency  spectrum  and  interest.  A third  important  in  detectors  to  a  therefore source  the  due  For (REF  are  of  high  noise,  the  band  frequency  leakage  by  flicker  frequency  i t s 1/f  given  limited  bandwidth noise,  of  of  is  interest  not  for  SS  expected  is  spectrum.  current  I  , the  noise  8) <i  >  2  n  = 2qBI ^ s  ( i  +  ^  e  V  /  K  T  )  Equat ion where  q  is  interest, energy. the  V  the i s the  The  Shockly  Empirically, tenth  of  the  The  electronic bias voltage  second  (thermal)  diode  equation  one  detect  can  m a g n i t u d e of  leakage  diffusion  generation  current  the  D  P  R  =  V  is  A  the  =  the  respective  intrinsic in  the  been  pulse  of  temperature  simplified  using  conductance.  approximately  one  current.  partially  (first  (second  bandwidth  calculate  leakage  current  is  term has  is  i s the  kT  to  the  B  described  term, E q u a t i o n  term, e q u a t i o n  2.15)  by  the  2.15)  and  i n a pn  step  Equat ion  2.15  diode:  J  where  and  a current  current  theoretical  junction  charge,  2.14  carrier  q / V  r  p '  diffusion  hole  and  (  n  i  W  N  D  )  +  constant electron  concentration,  n r e g i o n , and  V  i s the  N  Q  q  n  i  W  /  T  e  for holes, lifetimes,  i s the  donor  r  P n^  and  r  e  is  are the  concentration  depletion width. R e c a l l that  the  intrinsic (Equation thus  carrier 2.3) w h i l e  has  carriers  a  of  lifetime  strong  is  also  recombination Further  concentration  reduced in  contributions  detector  from  as w e l l  device.  In  the  emission  surface  states  often  Leakage  detectors  i s the p r i m a r y  Leakage c u r r e n t ,  causing  faults  a b s e n c e o f slow n e u t r o n s , dominates which and  radiation  in a d e t e c t o r lattice  damage  temperature diffused  devices.  have a l i f e t i m e  than  and  by  depleted  edges  voltage  leakage  of  room  the  dependent  current  current  and  in  the  temperature  for useful  i t is  current  isotope the  SS  devices.  -10  1 4  noise  production.  former  by  In t h e  mechanism  which traps  reduce charge  efficiency,  ions deposit  more e n e r g y  Heavy  sometimes  and  damage c a u s e s c h a r g e  times,  400°C) heat  1 1  the  required  Ion implanted  of 1 0  injection  p r o b l e m due t o t h e l a r g e  proportionately  can  (less  in  faults.  a totally  generation  to leakage  response  do  from  and  damage  leakage c u r r e n t . and  the  damage. L a t t i c e  slow d e t e c t i o n increase  to  depth  contributes  lattice  at  engineering  radiation  come  detectors,  current  and d e p l e t i o n  current  (generation  in  leakage  dominate  zone.  leakage  and by l a t t i c e  contact  contributes  depletion  Radiation  crystal  barrier  temperature  d e p e n d e n c e . The l i f e t i m e f o r impurities  the  back  with  the  to leakage current  surface  area  by  as r e s i s t i v e  Schottky  surface  decreases;  temperature  sites)  carriers  increases  be  more  damage.  annealed  treatment detectors  particles/cm  2  in  out  Crystal by  low  implanted  or  have been  shown t o  i n a muon f l u x  (REF  9).  Surface  barrier  detectors  tend  to  have  shorter  life  expectancies.  In  a  neutron is  a  slow  addition,  decay  will  Depletion  To  dopant of  and w i l l  the  zone.  phosphorus.  make t h e c r y s t a l in  the  energy  of  A stack  stopped  the p a r t i c l e  of t o t a l l y  measuring  medium  detector  energy  low e n e r g y  of  the  dead  of  low e n e r g y  limit  particle  zone  by  of i n t e r e s t  the  s u r f a c e and t h e d i s t a n c e The  dead  surface zone  zone  barrier  can  particle  be  as a  collimated  can  large  of r e s o l u t i o n  at the surface  characterized  active  SS d e t e c t o r s c a n  and a r e i d e a l  a single  depletion  solid  depth  i s r e a c h e d when  approaches  t o t h e edge o f reduced  The a b s o l u t e  the  source.  the  dead  of the  zone  is  on t h e zone.  of Angstroms i n  thickness  of  range  depletion  the energy  angle  state  the  the thickness  t o hundreds  e s t i m a t e d by m e a s u r i n g of  for  i s used.  t h i c k n e s s of the metal c o n t a c t s  detectors.  monoenergetic  stop i n the a c t i v e  of the d e t e c t o r . T h i s  be  function  i n an SS  t o low e n e r g y p a r t i c l e s o r  particles,  w i t h an a p p r o p r i a t e l y  The  detector  depleted  volume d e p l e t e d  X - r a y s . To measure  more n t y p e . In  particles  have more t h a n 99% o f t h e i r the  Phosphorus  resolution  i t i s necessary that  depletion  to  can absorb a  signals.  depth, energy  detector,  (3% a b u n d a n t )  Si  radio-isotopes  add n o i s e  measure  3 0  /3 d e c a y  and s u b s e q u e n t a l l y donor  region  neutron flux  of the  dead  of a d e t e c t e d  incidence  for  a  Transmission  SS  detectors  detectors  energy  loss  small  compared  detected is  pulse  primary  with  (^20%  Assuming  total  to  of  in  energy  energy  signal-to-noise ratio be  improved  According  p u l s e s . However,  surface high  higher  by  voltage,  implanted  barrier  devices  electric than  loss  is  particles,  the  energy  thin  of  a  substantial large  to d i s t i n g u i s h matter.  The  i s to detect  detectors  it  depleted  such a  loss in  detector  As  loss  the  Even w i t h  10  5  of  totally  i n c r e a s i n g the 2.7  and  i n c r e a s i n g the  in a t o t a l l y  resistivity  internal  the  energy  to Equations  become a p r o b l e m as of  the  their  the  and  particles  depleted  detectors  loss.  charge c o l l e c t i o n ,  voltages  energy  scattering, fully  a transmission  The  bias  of  by  d e p l e t i o n depth.  loss).  r a t e s of  energy  applied  the  r e s o l u t i o n i s used  low  the  particles  i s a l s o measuring  s i g n a l s a s s o c i a t e d with  device.  that  energy  reduce  one  different  problem  the  to detect  u s e d . When m e a s u r i n g  particle,  with  often  can  the  uncertainty,  can  up  are  straggle  particles  small  to  desireable  transmitted  built-in  used  i s p r o p o r t i o n a l to the  detectors  energy  often  in transmission.  normally  thin  are  depleted  injection can  bias voltage  across  2.10,  this  speeds  the  current  height  detector  current  at  breakdown e f f e c t s .  or d i f f u s e d PIN and  a l l types  intrinsic  regions.  field  exceeds  V/cm)  or  i f the  a  diodes  of  with  the  a  back  The are  large contact  breakdown l a r g e r than  behave b e t t e r w i t h Breakdown o c c u r s  critical  value  very i f the  (somewhat  d e p l e t i o n zone moves  through  the  back  contact  devices).  These  (or  front  processes  contact  are called  in  surface  avalanche  barrier  breakdown and  punchthrough r e s p e c t i v e l y . Minimum temperature taken 10"  particles  SS d e t e c t o r s  as t h i n  t o reduce  noise.  should  any SS  be  detected  as 100 microns  corresponds  s y s t e m .that Position  It  in  room  i f care  is  t o a s i g n a l of around  can  Less e x a c t i n g produce  SS  direction  the behavior  be o p t i m i z e d  electrodes techniques  reproduce techniques  strip  (REF-6).  strip  charge  to  behavior  the  readout  of the d e t e c t o r / e l e c t r o n i c s  f o r any g i v e n a p p l i c a t i o n .  limit  diffusion  length,  patterning  on t h e s u r f a c e  with  the  electronics  one m i c r o n  dimensions.  Kemmer  5 micron  et  a l to  r e s o l u t i o n i n one  r e s o l u t i o n was a c c o m p l i s h e d  an a m p l i f i e r on e v e r y between  the  of the d e t e c t o r .  for  have been u s e d by  This high  spacing,  a r e made by  features with  readout  third  using  s t r i p and  amplifiers.  The  on p o s i t i o n r e s o l u t i o n i n SS d e t e c t o r s may  t h e width of i o n i z a t i o n  8)  related  developed  detectors  interpolation  theoretical  (REF  the s i g n a l to noise  intimately  sensitive detectors  collecting  industry  Mm  that  resolution  Photolithographic  20  is  is  should  Position charge  be e m p h a s i z e d  detector  electronics.  be  This  can  electrons. It  of  ionizing  L,  tracks  of c a r r i e r s  in  SS  before  detectors they  or t h e  are collected.  L =  (Dt)  l / 2  Equation where D i s t h e d i f f u s i o n the  time  carrier  of i n t e r e s t .  constant  f o r charge c a r r i e r s  The d i f f u s i o n  m o b i l i t y u and t e m p e r a t u r e  constant  is  2.16a  and t i s  related  to  (REF 8 ) :  D = MkT/q Equation Electrons  in silicon  at  temperature.  room  integrated two  area  Detectors  detectors  made  with  more  feasable  fora  high  ns  CCD r e a d o u t s o r  make l a r g e a r e a  of e l e c t r o n i c s r e q u i r e d  a l l types  (passivate) the  detector strips. used  an a v e r a g e o f 6 /um i n 10  high  by  resolution  reducing  resolution  the small  detector.  In  in  diffuse  preamplifiers could  dimensional  density  will  2.16b  the  of d e t e c t o r s surface  environment the  8).  should  Two e x a m p l e s o f  i n t h e two p r o c e s s e s  is  important  of t h e s e m i c o n d u c t o r  (REF  surface  i t  In  a  position  be p a s s i v a t e d  surface  passivation  described  to  from  protect  impurities  sensitive  between  electrode  techniques  i n Chapter I I I .  SS  are  CHAPTER I I I FABRICATION OF  With a r e c o g n i z e d decided  that  fabricated  position  a t UBC.  commercially  but work  Engineering  Solid  Kemmer by  England  proved be  al  to  be  emphasized  Ion  implanted The  1980  is  was  6)  in t h i s  and  SS  surface  and  should  be  available  expensive.  in  the  The  was  main  Electrical t h r u s t of  techniques  barrier  surface  The  used  techniques  barrier  more s u c c e s s f u l , and  the by used  technique  will  therefore  detectors detector  a standard  PIN  of  flow  chart  (Kemmer  claims  40  developed  diode  strips  is attractive  so a s  2  Also  t o be  contamination  possible  make  a  low  Kemmer  (REF  6)  in  in Chapter  II,  but  position sensitive.  in Figure i t s very  3.1.  low  desireable  after leakage  i s the  detector  type  A of  current  w e l l above  the  q u a l i t y of  the  almost  fabrication. SS  This  leakage  even when b i a s e d  t h a t makes t h e  environmental  by  described  i s shown  nA/cm ),  passivation  as  b e c a u s e of  depletion voltage.  to  very  implantation  the  are  it  discussion.  detector  surface  still  primarily  ion  devices  devices  Laboratory.  the  simpler  made i n a p a t t e r n  total  done  a t TRIUMF,  silicon  3,5,12). E n g l a n d ' s  implanted  fabrication  are  State  (REF  (REF  detectors  sensitive  they  to reproduce et  f o r SS  Position sensitive  fabrication  work was  need  DEVICES  detector  It  immune was  using  to not  this  FIGURE  3.1  C l e a n 5000K wafer  n  type  Grow 2000A o x i d e ( l O h r s 1040C d r y oxygen)  Pattern oxide with photolithography  Implant Arsenic  Anneal (30min  Boron (15ReV 5 x 1 u ' % m (30KeV 5x1 O'Vcm' ) 3  i m p l a n t damage 600C i n n i t r o g e n )  D e p o s i t aluminum by e v a p o r a t i o n (1000A)  P a t t e r n aluminum photolithography  by  Kemmer's i m p l a n t e d d e t e c t o r f a b r i c a t i o n p r o c e s s . Note t h a t t h e s i l i c o n s u r f a c e i s p r o t e c t e d from t h e e n v i r o n m e n t by e i t h e r aluminum o r s i l i c o n - o x i d e ( R e f . 6 ) .  3  technique built was  i n the development  using a modified  not  uniform  The  process  strip  to  most common p r o b l e m  cleanliness.  The  contamination clean  from  time  The  cleanliness  E.E.  like  controlled.  Wet  impurities  to  temperature  steps  The  dry  steps  like  the  resistivity  steps  bulk of  in  10 juA/cm  this  and  2  of  the  the  of  crystal  process  i f a highly for  is  make  controlled  the  fabrication  lacked this  quality  steps.  i s not  photolithography  regions  In  of an  completely  can  introduce  d e t e c t o r w a f e r and annealing  can  high drive  detector.  lattice  High temperature  the  detector  state fabrication  l a b o r a t o r y that  and  the  of  processing  .oxidation  history. of  a t UBC wet  surface like  integrity  temperature  and E.E.  the  its  solid  available  the  the  into  i n any  not  best  strip.  laboratory  i n both  environment  impurities  is  The  a leakage  t h e w a f e r more l i k e l y  environment  process.  had  l a r g e number of  of  available.  semiconductor  i s a l s o dependent treatment even  in  on  can  lower  a  clean  e n v i ronment.  Since the  ion  crystal  temperatures. the  anneal  process  this  be  damage  or  must  t e m p e r a t u r e as  process  is  very  ions d i f f u s e  lattice.  themselves annealing  a l s o damages t h e  The  dopant  crystal  i m p l a n t a t i o n doping  At  move  necessary  the  a  f u n c t i o n of  important.  and  are  same t i m e ,  towards  annealed  the  i s dependent  out  During  crystal  surface.  at  time  incorporated the  s u r f a c e of  The  high  used the  in  anneal  into  the  faults  heal  amount  of  upon t h e e n e r g y and  dose  of  the  implanted  "activation" crystal  (REF  atoms  and  (the percentage  lattice,  recommends results  dopant  the  rest  annealing  at  600°C with  recommend  (REF 1 3 ) . The a n n e a l  leakage  current  experimentation An  option  annealing  be  Kemmer  process  before consistent r e s u l t s extensive  temperature deposit  to  laboratory  at  to  temperature  short  certainly  this  anneal  affects  detectors,  and  process  the  further at  UBC.  i n the f u t u r e i s s u r f a c e  can  probably  be  a  another  be . a c h i e v e d control. techniques oxide. better  A  without  F o r example, c o u l d be  the  lower  used  RCA  to  before  cleaning  i t i s not always  process  carrying  laboratory  surface etch  than  fabrication  a  from  one  out a time-consuming  SS d e t e c t o r s  A surface barrier  fabrication  process  y e a r s ago a t t h e U n i v e r s i t y  Si/Si-oxide/Ge  in  procedure.  barrier  (REF  have t o be m o d i f i e d  UBC. G e n e r a l l y s p e a k i n g ,  transplant  to  redevelopment  ten  will  environmental  prove  used  possible  England  f o r 16 h o u r s  considered  mask/passivation  may  technique  than  an 800°C a n n e a l  process  s p u t t e r i n g or plasma  the  oxidation  Surface  Kemmer  w i t h h i g h power a r c lamps.  The  without  i n c o r p o r a t e d into the  but the best  implanted  may  dopant  interstitial).  i s required to optimize  that  desired  f o r 30 m i n u t e s ,  high  processes  of  the  of dopant  remaining  a t UBC were a c h i e v e d  14). Others  upon  10). H i s tunnel  detector  diode  on  is both  was d e v e l o p e d  of B i r m i n g h a m an  n"  surfaces  wafer  more  by J.B.A. with  a  ( F i g u r e 3.2).  FIGURE  3.2  11OOA A l 650A  Ge  20A-50A SiO,  2 30/un S i (5000.rt.cm n t y p e )  W/1777777777777777777Z  C r o s s s e c t i o n of t h e s u r f a c e b a r r i e r s t r i p d e t e c t o r b u i l t a t UBC ( m o d i f i e d E n g l a n d t e c h n i q u e , R e f . 3,5,10,12). F r o n t and back a r e i d e n t i c a l e x c e p t f o r p a t t e r n s i n aluminum.  Surface  electrodes  resistance  of  sensitive  detectors.  requiring  only  probability  the  of A l or Au  in  the  degraded. in  detector  process  Surface  r a d i a t i o n and,  similar  of  and  surface  reduce  fabrication  process  or  other  thus SS  a higher  The  low  barrier  short,  reduces  mistakes  do  devices  not  have s h o r t e r  and may  100°C  are  leakage c u r r e n t  cost  simple  the  during  above  properties  detectors  sheet  is  i s never heated  i t s bulk  the  for position  laboratory. This  crystal  in theory, device.  to  a pattern  i n the  barrier  implanted  fabrication  day  used  to provide  contamination  The  England  and  The  one  of  manufacture.  device  are  lives  than  process  make t h e s e  a for  problems  unimportant.  The  r e c i p e d e t a i l e d i n Appendix  attempts  at  duplicating  slightly  modified  leakage  detector  with  aluminum  proved  t o be  As  water  quite  It  distilled,  are  were  found  must be by  (REF  Several  of  several  and  is  only  12).  Two  low  this  process  parts  of  the  process  cleanliness  is  of  primary  that  w a f e r s t h a t were not  large leakage c u r r e n t s ,  England  also claims  enough f o r the  filtered,  protected  process,  fabricated using  mentioned,  with  clean  best  important.  was  cleaned.  i s not  chemicals  wafers  metalization.  produced diodes carefully  England's  i s the  from h i s r e c o m m e n d a t i o n s  previously  importance.  A  very  deionized clean  epoxy  and  and  even  that deionized  process  and  pure. Only surface  after is  were  filtered  recommends  water. S i m i l a r l y ,  the  i f they  etched  only  u t e n s i l s and the  edges  protected  by  germanium of  the  i s the d e t e c t o r r e l a t i v e l y surface.  passivation  due  impurities); England  However,  provides  its  gettering  effects  to  i s one  of  it  surface  was  was  prevented  the  to choose  excellent (ability  of t h e a t t r a c t i v e  the  left  surface to  properties  e t c h d i d not  provides  of  the  trap of  quick quenching or  rippled.  the etchant (wafer  the  appear  to  device.  agitation  T h i s perhaps  from  effect  ideal  of the e t c h , the  slightly.  reduced  an  final  even w i t h c o n t i n u o u s  mottled  surface  surface  thickness  that  careful  by d i l u t i n g  each  silicon  found  e t c h b a t h and  uneven  germanium  contamination  surface barrier detector.  opportunity  from  from  The  this  Etching  the  safe  With 250  the  Si  could  10 um  t o 230  of  be  removed Mm),  the  of  the  behavior  detector. The surface  t y p e o f epoxy u s e d  for  barrier  is also  must c o v e r the  detectors  t h e a r e a not  CIBA epoxy  viscosity  to  s u r f a c e (another  These  are  conductive them  s o u r c e of  "amine  silicon.  necessary  as  l e a k a g e . They a r e  England  l o n g as  from  current which forming  the e v a p o r a t e d  found films  epoxy 50  and  t o have of  low  touching  recommends p a s s i v a t i n g I t was  these  epoxy  are designed  epoxies,  layer  w i t h epoxy b e f o r e e v a p o r a t i n g Ge. not  Transene  leakage  type"  surface inversion  i n the  ohmic  of  i m p o r t a n t . The  t h e c h a n c e of an a i r b u b b l e  silicon  also  very  i n A p p e n d i x A)  to prevent  reduce  passivation  p r o t e c t e d by Ge.  (mentioned  a high r e s i s t i v i t y  edge  that  (REF  the 3)).  prevent  a  underneath the  edges  this  was  were kept  away  FIGURE 3.3  EVAPORATED A l CONTACT  CIRCUIT BOARD  SILICON  EPOXY  Cross s e c t i o n of the d e t e c t o r edge p a s s i v a t i o n .  circuit  board  mount and  from t h e w a f e r edges The p r o c e s s t o make c o n t a c t is  developed  mask.  shorting wafer (used  strips  be  thin  evaporation  film  (Figure  through a s i n g l e  shadow  however,  to avoid  electrically  i f t h e shadow mask c a n n o t  touch  the  Ultrasonic  wirebonding  industry)  is  t o make e l e c t r i c a l  contact  t o be t i m e c o n s u m i n g , f r a g i l e  s t r u c t u r e of a s u r f a c e  3.3). I t contact  i n the semiconductor  tends  evaporation  t o do b o t h t h e  t h e epoxy ramp i n t h e way.  available  Wirebonding  board  by E n g l a n d ,  taken,  together  extensively  technique  the  must  with  uses a second A l  t o the m o u n t i n g c i r c u i t  and t h e s t r i p  Care  3.2).  a t UBC  p o s s i b l e , a s recommended  evaporation  is  (Figure  another  to the wafer. and may  damage  barrier detector,  and so  n o t recommended.  Preliminary  electrical  characteristics  of  surface  barrier  detectors Before  mounting  leakage current to assess  the  t h e q u a l i t y of t h e  greater  prevent crosstalk sheet  than  crosstalk. but  is  the input  strips  resistance  and  100 Kfl. T h i s  between  strips  was  the  measured  on  the  detector  must  be  impedance of t h e p r e a m p l i f i e r s t o  Capacitive not  wafers,  devices.  coupling  so e a s i l y  r e s i s t a n c e of t h e germanium  the  detector  and t h e r e s i s t a n c e between  The r e s i s t a n c e between much  completed  strips  can  also  lead  to  measured o r c o n t r o l l e d . The layer  was  is  enoug'h  that  measured a t between  40 Kfl  i s more t h a n a d e q u a t e s t r i p  high  isolation.  To  measure  to apply  a bias  flowing  in  leakage c u r r e n t , voltage  to three  the  middle  situation  similar  to  detectors  produced  typical  t h e w a f e r was  voltage.  The  wafer with the  the  symmetric  biased  was  the rest  voltage  with  field  detector  while  the f r o n t  will  now  expected  be  in  current  when p a r t i c l e s  biased  than  high  detector.  pulses  are  will  i s forward negative.  current.  leakage  strips  that  was  tested.  In  theory,  of e i t h e r  polarity.  to  Symmetry  a  s i d e of  is  from t h e f r o n t negative  When  or f r o n t  junction  the  detector  reverse  toward the  biased  detector  be seen on t h e d e t e c t o r Similarly,  a  positive  t h e back j u n c t i o n r e v e r s e  biased;  the  above  produce a  detected.  have  this  50%  should  barrier  this  at  o f t h e I/V measurements i n  the detector  current  biased pulses  i n the leakage c u r r e n t  but n o t o b s e r v e d . A n e g a t i v e  leakage  more  these  techniques  surface  3.5.  acceptable  depleted  i s a p p l i e d to the patterned  the f r o n t  positive  seen t o be  i n the d e t e c t o r  a voltage  r e c i p e had a  pictured in Figure  being  that  the  The  quite consistent across  results  of  current  be m e a s u r e d i n a  England  totally  and ,the d e p l e t i o n zone^ grows  causes  lower  be  found  manufacturing  b a c k . The e l e c t r i c  strips  later  t h e asymmetry  detector,  modified  to  The  used  configuration.  a t -30 V was  behavior  than  can be b i a s e d  negative the  expected  I t was  then  (I/V) b e h a v i o r  of the s u r p r i s i n g  l a b was  that  the  one o r two s t r i p s  were more n o i s y  One  could  p r o b e was  strips.  operating  per s t r i p  I/V  only  average.  with  voltage  1 MA leakage  The as  current  adjacent  strip the  a multipoint  b i a s proved  T h i s asymmetry  can o n l y  to  give  was a  be c a u s e d by  FIGURE  D  E  T  E  C  T  O  BIAS  L e a k a g e c u r r e n t o f one s t r i p  detScto? ° V  l t a g e  r e v e r s e  R  3.4  S  T  R  I  VOLTAGE  P  3  6  (V)  (1 mir,X30mm) i n t h e SS d e t e c t o r the patterned side  biases  of the  the  different  patterned, surfaces epoxy, that  back  are the  puzzling  i n the  characteristics  All  solid  There  Preliminary  and  that  ready  as  England  an  with  the  constant  also  the  mounted  in  3,  indicating Even  of  more  in  charge IV.  is  of  seen  This  type  charge  asymmetry  Current  surface  voltage barrier  expected.  act  surface  to  is  some  barrier  aluminum  increase  device  tests  were  responsible.  Chapter  this  (front  qualities  wafers  was  in  state detectors  i s roughly  manufactured  the  other  detector.  discussed  however,  all  layers  r e d u c e d t o a f a c t o r of  finished  s e e n when the  increase  as  asymmetry  from p h o t o n s by  is,  current  an  The  aluminum  partially  symmetric  photodetector. shielded  was  show  i s not  the  After  are  that  further  detector  not),  effects  collection  of  identical.  is  be  is  asymmetry  edge  will  geometry  of  and  extent  detector  3  in  ixh/cxn  2  showed  that  the  layers. leakage  daylight.  at a l l non-zero b i a s  modified  England process  f o r charged  particle  tests.  This  voltages.  detector  the  a  i s mostly  germanium  about  operated  like  were  wafers acceptable  CHAPTER  IV  SOLID STATE DETECTOR SYSTEM TEST A  detector  surface were  barrier  performed  detecting  a  amplifier detectors on  system  the  ratio  system  of  the  A l s o measured was  efficiency  for alpha  beta  charge  1 mm  using  the  beam t e s t s  efficiency  particle  s y s t e m . The  the  Pion  t o measure the  charged  confirmed.  and  assembled-  m a n u f a c t u r e d a t UBC.  transmitted  signal-to-noise  was  for  and  the  resolution  was  generation/collection  particles.  Preamplifier electronics The current Italy  preamplifiers sensitive thick  (part  silicon with  low  detectors input  detectors  is their  inch)  low  and  gain  was  For  small  linear  or and  detector. gain  1  high  noise  and  behavior  prototype  system  a v a i l a b l e from L a b e n  negative  pulses.  lower  have  (15  high  speed  noise  good  (four nA  the  In  summary,  and  higher  D i v i s i o n e L a b e n , 20133 M i l a n o ,  telex  the speed  in  1  strip square  input).  The  circuit. for  amplifiers  are  than  the but  photograph  312451  for  equally well  i t s behavior, A  per  prototype  work  are  risetime)  useful for  equivalent  amplifiers  useful.  ns  channels  RMS  for observing  been  (2  Particularly  (4±.5) mV/juA i n these  of  are  density  signals  They a r e  would  the  hybrids  impedance.  measured a t  positive  film  for  number MSD2). T h e s e a m p l i f i e r s were d e s i g n e d  strip  a  used  silicon higher of  the  FIGURE 4. 1  C u r r e n t s e n s i t i v e p r e a m p l i f i e r a r r a y . In s p i t e o f t h e h i g h d e n s i t y Laben h y b r i d s , two l a y e r s of c i r c u i t b o a r d s a r e used t o r e a d o u t t h e 20 s t r i p s from e a c h s i d e o f t h e detector.  45  FIGURE  4.2  10  KJT  " W W  BIAS VOLTAGE  '  .01  MF  to Cu  I—I  EH W  in  a o  a. EH  EH  D  D  EH U  o  H  EH W Q  LABEN  MSD2  AMPLIFIERS  P r e a m p l i f i e r  a n d  b i a s  v o l t a g e  c i r c u i t .  detector/preamplifier circuit Alpha  diagram  source  i s shown  tests,  Charge  asymmetry  efficiency  and  Figure  side  4.3  alpha  can  shows  of  preamplifier. MeV  by  2.2  generation  times  from the  observed  the  voltage  i n these  2.10;  times  A  collection  on  energy  is  the  seen  hole as  in this  fmC  estimated  the  t o be l e s s  gain  pair). the  1/3  than  20%.  and a d j a c e n t  4.8  charge  expected. of  as e x p e c t e d  c o n f i g u r a t i o n i s as expected strips  to  This  4.3  the  o f k=.34 i n  a r e on t h e o r d e r  t o be a s f a s t  from  of  when r e d u c e d  of 7 n s . The c h a r g e c o l l e c t i o n  between a d j a c e n t  in pulse  i s i n c r e a s e d . The  gives a value  same  calculations were  and  i s 5.8 MeV;  electron  junction  arid i n c r e a s e  i s 230  of a i r , t h i s  the  seen f o r  b i a s v o l t a g e s . The  bias voltage  pulse  pulses  the p u l s e s p i c t u r e d i n F i g u r e  on t h e o r d e r  .Crosstalk  of the  signals.  charge  source  of p u l s e width  the d e t e c t o r  efficiency  detector  in  several negative  as  The a l p h a  collection  Equations  particle  observed  2  (3.3 eV p e r  Uncertainties The  seen  l o s s e s i n 1 cm  Equation  alpha  from a ""Cm  shortening  be  area  characterictics  the p r e a m p l i f i e r output  particles  charge c o l l e c t e d the  asymmetry  with  of the d e t e c t o r w i t h  height  a  4.2.  and g e n e r a t i o n  was  4.1, and  time.  characteristic  the  detector  measured  striking  i s included in Figure  in Figure  collection  SS d e t e c t o r were  detected  system  have  20%. from rise  behavior from  of  theory.  amplifiers  was  47  FIGURE  c)  BIAS=-32V  4.3  d) BIAS=-39V  C u r i u m 244 a l p h a p u l s e s f o r d i f f e r e n t b i a s v o l t a g e s (measured after the p r e a m p l i f i e r s ) . Notice that charge c o l l e c t e d (area of p u l s e ) i s r o u g h l y c o n s t a n t w h i l e t h e p u l s e h e i g h t and r i s e time vary.  ALPHA SOURCE ON FRONT SIDE  ALPHA SOURCE ON BACK SIDE  Response o f d e t e c t o r t o 5.8 MeV a l p h a particles for different b i a s p o l a r i t i e s and s u r f a c e s of e n t r a n c e f o r t h e p a r t i c l e s . S k e t c h e s o f t h e i n t e r n a l e l e c t r i c f i e l d and t h e i n i t i a l ionization d i s t r i b u t i o n a r e i n c l u d e d . The l e f t hand s i d e o f t h e s k e t c h e s r e p r e s e n t s t h e f r o n t o f t h e d e t e c t o r ( p a t t e r n e d s i d e ) where t h e p r e a m p l i f i e r s are connected.  When placed the  the  on  the  behavior  pulses  bias  opposite changes  observed  voltage  observations  can  the  the  detector, of  the  The pulse) the  charge i s seen  front  or  voltage). this  of  voltage slightly  electrons. trapping the  of  bias  shown a r e  distributions.  the  the  the  These  d e p l e t i o n depth  efficiency  and  the  of  drift  the  the of  detector  V.  The  V,  detector a  the  the  same r e s u l t s  at  32  in  that  pulse  for holes  effect  three seems  for electrons  most  (-area  entering a  28  depleted  were not the  either  given  Mm'in  bias  silicon,  at  seen  of  a at  detector  bias a  bias  is  only  V.  areas  voltage  is  i s at  zone  (for  is totally  indicating  bias  depletion  seen  for  indicates (negative times  to  that  bias  better  indicate  either  i n the  different the  voltage than  the  charge on  the  that  for  presence  crystal  bulk  or  of in  surface.  The a  range  side)  sites  to estimate  Also  of  the  This  shows  back  efficiency  strip  4.4  carriers.  difference  collection  Figure  combinations  ionization  is  junction,  same f o r a p a r t i c l e s  of  source  the  position.  collection  alpha  from  the  ±25  polarities  front  charge  way.  possible  and  used  over-depleted  The  detector  t o be  ±32  of  field  the  in  implies that  voltage  four  or  deposited  the  As  the  source  be  charge  of  in a mysterious  and  electric  i s reversed  side  for the  polarity  qualitative  time  voltage  extreme widening  particles  enter  on  the  of  the  detector  non-junction  side  pulse of  the  seen  when  the  detector  is  another  unexpected  Equations the  2.10  collection  electrons,  the  space charge  Beta  where  to  from a  1 0 6  Rh  which  is  result the  addition,  f o r h o l e s than  This  is  pulse  time  deposited.  can p o s s i b l y electric  The  be e x p l a i n e d  field  due  to  by the  particles.  s o u r c e were u s e d transmitted  |3 d e c a y s  are  almost  the  voltage  effect  electronics  30 ns  for  further  from  1 0 6  urn of  by  the  long  detector. a r e shown  and  show  seen,  asymmetry  p u l s e s from a n e g a t i v e b i a s e d  of  however,  the  no  pulses.  negative to p o s i t i v e .  tests  Ru  t h e low end o f  for a particle  is still  i s s w i t c h e d from  i n 230  to 0 p a r t i c l e s  lengthening observed  reduction  particles.  w i t h a peak e n e r g y of  stopped  response  4.5. The p u l s e s a r e a b o u t of  to observe the  by t h e 0 p a r t i c l e  lost  of the charge c o l l e c t i o n  positive  energy  by a  signal  of t h e d e t e c t o r  1/3 c h a r g e bias  data.  250 KeV when p a r t i c l e s  spectrum  Photographs  the  about  Ru  i n turn  silicon  energy  1 0 6  to small  The peak e n e r g y  The  a  the  on t h e l o c a l  3.5 MeV.  evidence  In  tests  response  Figure  ns.  by  with the a b s o l u t e s t r e n g t h of  from E q u a t i o n s 2.10  particles  decays  time p r e d i c t e d  t o be l a r g e r  the  is correlated  effects  source  detector  in  in  charge d e n s i t i e s ^ g e n e r a t e d  0  the  t h e o r d e r o f 20  i s n o t seen  field  discrepancies  The c o l l e c t i o n  times are p r e d i c t e d  effect  electric  large  a r e a t most  which  lengthening  effect.  when As a  prototype,  were d e s i g n e d t o r e c e i v e detector.  FIGURE  4.5  20ns p e r d i v i s i o n 5mV p e r d i v i s i o n  D e t e c t o r p u l s e s seen from a R u t h e n i u m 106  ( a f t e r p r e a m p l i f i e r s ) f o r beta source.  particles  52  FIGURE  4.6  5mV/div 20ns/div  Noise  seen  at output  of  preamplifiers.  Observed  noise  of s y s t e m  The  noise  seen on an o s c i l l i s c o p e  preamplifier  was about  1 mV peak  i n the  output  (.2 M A RMS  to'peak  of  equivalent  input  t o p r e a m p l i f i e r ) ( F i g u r e 4.6).  What  is  that  this  with  bias voltage  detector noise  noise  or with  appeared  did  not  exposure to  change  of the  be m o s t l y  spite  of the s p e c i f i c a t i o n s ) ,  when  the  only  be a c h i e v e d  voltage, of  detector  as  detector  caused  The  daylight.  slightly  low n o i s e  was u s e d  The  reduced  behavior  could  f o r the d e t e c t o r  t o be a s i g n i f i c a n t  bias source  design prototype  detector  was  tested  b e a m l i n e a t TRIUMF. The e f f i c i e n c y measured  for  different  different  settings  a l s o made o f t h e possible  of  noise  detector level  was t o o low  one w a f e r was t e s t e d  The  detector  acquisition  as  types  by  three  and  bias voltage.  of  M13  pion  the  was  energies  at  Estimates  were  system.  It  was  not  r a t e performance of the d e t e c t o r during  was  the  linked  shown i n F i g u r e  p r e a m p l i f i e r s on t h e 40 d e t e c t o r  individually  the  experimental  time.  extensively.  system  system  in  for detecting particles  particle  t o measure t h e h i g h  t h e beam f l u x  Only  the  on t h e  noise.  Beam t e s t  as  is  by t h e p r e a m p l i f i e r s ( i n  was removed. T h i s  power s u p p l i e s p r o v e d  interesting  to  a s i t was o n l y  when a b a t t e r y  the  LeCroy  to  the  CAMAC  4.7. The s i g n a l s  data from  s t r i p s were d i s c r i m i n a t e d  2735A  u n i t s . The l o g i c a l ECL  CD  a w  SOLID STATE DETECTOR  ANALOGUE SIGNALS 40 CHANNELS MALU GATES, TDC START FROM SCINTILLATOR COINCIDENCE  Block diagram of d e t e c t o r f o r t h e p i o n beam t e s t .  data a q u i s i t i o n  electronics  output by  pulses  CAMAC  from  majority  discriminators size  do n o t g i v e pulses  In  to  addition  delay  line  could  Y direction oriented  a n d 2 mm  beamline With  was  e . +  channel  Heavier  particles  The p i o n  energy  the  set  96 M e V / c  flight  information,  minimum available  Beam t e s t ,  up  f o r each  position  Measurement  of  8%  i s possible  observed. t o more  f o r the test.  recorded  performed  i t  i n each event ionizing  (Figure  The  1 mm The  vertical  strip  detector  values  during  (slits  open t o  pions)  9 5 % n*,  A  range  than  twice  first  i s 50 MeV.  With  the f r a c t i o n By u s i n g  of  time  of of  the  three  particles  from  minimum  30,000  3%  i n the  to distinguish  Approximately detector  i n the  i s roughly  each.  4.8).  direction.  a t t h i s momentum ( 3 0 MeV  delay-line and  are stopped  a n d muons g o e s up t o a b o u t  particles  were  at  the  f o r ray tracing  momentum  t h e beam  so  directly.  two  s e t a t 128 M e V / c  scintillator. channel  of  room  amplifier  output  i n the Y  s e t a t two  1 0 % A p / p momentum w i n d o w ) 2%  the  sensitive  give  electrons  used  for a trigger  test.  and  signal  i n the X d i r e c t i o n .  t o be p o s i t i o n  2735A  detector,  chambers were  the  +  The  n o t be r e c o r d e d  strip  were used  i n the counting  units.  chambers had a r e s o l u t i o n  T h e M13  M  read  an a n a l o g u e  the  proportional  two s c i n t i l l a t o r s  was  logic  of the s i g n a l  multi-wire  or  t h e 2735A's were  ionizing  detector  was  events  configuration.  resolution the  by r a y t r a c i n g  SS d e t e c t o r with  the wire  position  resolution  chambers. This  was  was done  FIGURE  S C I N T I L L A T O R W I R E  C H A M B E R  2 2Q  (1 3 c m x 1 3 c m )  W I R E  C H A M B E R  1,  (13cmx13cm) S O L I D  S T A T E  D E T E C T O R  S C I N T I L L A T O R  1  w  EH  z w o  4.8  FIGURE 4 . 9  40 39 39 38 3E 37. 37 36 36 35 35 34 34 33 33 32 32 31 31 30 30  0 5 0 5 0 5 0 9 0  IEI  :iBX . . :l»K:  . . . .  :IBS: :I»S:  :t*S :ICS.  e  : «•«. :  E z o  :  :Xf  24 13 23  :X»S : : IH, :  I—I  in O cu  :X««,:  21 C 20 20 19  ::>•••: : IMi:  K O  : ft. :  . : tS*.: . . . :  ECJ H  :X««i :ICS.:  ca  :ISSI  a  S»,:  to  . . : l»Si: : iSS. 9. 5 : 9 0 I B 5 : 6 0 : 7 5 1 7 o : 6 s : 6 0 - . 5. 9 : 9 o : 4 9 : 4. 0 i 3. 9 1 3 o : 2 5 : 2 0 : 1 9 : l o -  . : . >Gi: . IS. : . .  1  I . 1  -I  OO  -0  50  WIRE CHAMBER  0.00  0.90  t o o  1 50  a. 00  3.90  TRACEBACK (cm)  S c a t t e r p l o t o f SS d e t e c t o r p o s i t i o n ( s i n g l e o r a d j a c e n t d o u b l e h i t s ) v e r s u s w i r e chamber t r a c e b a c k p o s i t i o n .  FIGURE 4.10  «0 3<f 39. 3B 3B 37 37 36 36. 35 35 34  34 33 33 3; 3?  31 31  30 30 2" re  E  2B 17. 27 St  z o  I>II>X<:.:X  co O a.  a  o  E-<  u w  • ISS. i i S X i i X i X i X X i S i i I n I S . I S I C . I M M . X I . X i . X . S S . • X X S i X >SX».  i.XS.  X.SXiS'SiIIXXSSX  E->  o co CO  WIRE CHAMBER TRACEBACK (cm) S c a t t e r p l o t o f d e t e c t o r p o s i t i o n v e r s u s w i r e chamber traceback with only "noise" included. Note t h e e x c e s s n o i s e on s t r i p s 17 and 23.  FIGURE 4.11  ' ''''''''I''•''' '''I'  360.  III  iiI ii  K I I I  —  240. — j  120. — I  WIRE CHAMBER TRACEBACK  (mm)  W i r e chamber t r a c e b a c k p o s i t i o n a t d e t e c t o r f o r h i t s o f s t r i p 20. N o t e t h a t t h e r e s o l u t i o n o f t h e WC t r a c e b a c k o n l y 1mm a t b e s t .  more  to  test  noise  than  traced  wire  i s shown back  analysis. and  of  traceback  in Figure  of t h i s  SS  from  the  Beam t e s t , The  noise  on  KeV  accomplished  fired. is  the  This  were  i n Figure  detector that  were  considered for of  strip  i s e x a c t l y what  one  mm  expects  r e s o l u t i o n instruments.  scatterplot  20  4.11. The 1.5  diagonal  was  found  ionizing  to  The  (Figure  have  particles  RMS  has  low about  .16 ULA b a s e d  i s a s i g n a l of o n l y  noise  a  lose  w i d t h and 3.2 eV p e r e l e c t r o n h o l e  rejection  by r e j e c t i n g hit  A typical  shown  particles  A  been  pair.  The  measured  at  detector  was  .2 uA ( F i g u r e 4 . 5 ) .  Preliminary  strip  4.11  Minimum  preamplifier/detector  one  versus  the c o r r e l a t i o n  system  i n the d e t e c t o r .  approximately  Only  resolution.  efficiency  ratio.  a 30 ns p u l s e  mm  as n o i s e .  prototype  signal-to-noise 90  and  1  traceback  o f two 1 mm  do not l i e on  4.10) were c o n s i d e r e d  give  i s shown  o f t h e peak i n F i g u r e  a p p a r a t u s and t o measure  detector  plot,  position,  correlation  Y  4.9.  the  width  events that  strips  chamber  through  A slice  experimental 1 mm  t o show t h a t  scatterplot position  the t o t a l  unless  of n o i s e  a l l detector  events with  i t was a p a i r o f a d j a c e n t  beam p r o f i l e  a s m e a s u r e d by t h e  in  Figure  4.12. H a l f  where a d j a c e n t  strips  fired.  as  the  flux  MHz  i s pileup a  beam  i n the s t r i p  Real  integer bins  than  strips  that  SS  detector  represent  events  d o u b l e e v e n t s were r u l e d o u t  was t o o low (1 K H z ) ; o n l y  non-negligible  more  problem.  at f l u x e s over 1  This  multiple  hit  FIGURE  1  80Q\  1  200.  4.12  60Q.H  Beam p r o f i l e Half integer  as seen w i t h the s o l i d s t a t e d e t e c t o r . bins represent adjacent double s t r i p h i t s .  noise  rejection  signals  equal  detected.  system  will  identify  to the p r o b a b i l i t y  of  p a r t i c l e pulse  signal  i n t e r p r e t e d as a r e a l  the  be  noisy  detector fired  per p a r t i c l e  i s shown  particles  and  that  noise  rejection  Efficiency the  through  peak  in Figure  were t r a c e d  can  and w i t h  is  defined  SS d e t e c t o r  The  noise  with  the wire  i s defined  rejection  is  apparatus.  The it*  e f f e c t of of  the  of s t r i p s  i n b i n zero  through the detector  4.14  shows  the  detector  the r e j e c t i o n a s t h e number  as d e t e c t o r  method d e s c r i b e d of p a r t i c l e s  no  above.  detected  by  t r a c e d back t h r o u g h i t .  events  (Figure  t h a t do n o t c o i n c i d e  4.10). S t r i p s  17  and  amount of n o i s e .  noise  mostly  that  noise  d i s c r i m i n a t o r t h r e s h o l d with  chamber t r a c e b a c k  residual  of p i o n s  4.13; e v e n t s  d i v i d e d by t h e number  23 show an e x c e s s i v e  The  versus  a  efficiency  back  being  t h e d e t e c t o r or  a t low d i s c r i m i n a t o r t h r e s h o l d s . The number  efficiency  f,  the  of n o i s e  particle  e v e n t . The l a r g e s t  were n o t d i s c r i m i n a t e d . F i g u r e  noise  real  i s not d i s c r i m i n a t e d  s y s t e m was t o r e d u c e  represent but  a  O n l y when no p a r t i c l e p a s s e s  when a r e a l  a percentage  due  lifetime, decay  seen  after  to pion  decay  r , i s 2.6 X  i n a short  multiple  hit  noise  t o muons i n t h e t e s t  10~  distance  8  s. The  fraction,  x is  f =*X//3C7T  Equation where | 3 , 7 , a r e t h e r e l a t i v i s t i c the in  pion  parameters  i n t h e l a b f r a m e . F o r 50 MeV  t h e 30 cms between t h e s t r i p  detector  pions, and  4.1  associated  with  4.2% w i l l  decay  the  final  wire  FIGURE 4.13  i  24000.  i i i i i i i i I i i i i i i i i i  i  _  —  16000.  8000.  L  —  ~Tjn  0.  5. 0  24000.  —  16000.  —  8000.  —  5. 0  I60QO.  —  I i ' ' •  24000.  —  16000.  —  8000.  —  -  8000.  I  I  I | I I I l I I I I l |-  5.0  10.  MULTIPLICITY THRESHOLD=1.0V  ' ' ' ' ' • ' ' ' ' ' • ' • ' ' ' i i  —  1 1 1 1 1 1 1 TTT"  - TI  1 1 1 1 1 1 1 1 0. 0  MULTIPLICITY THRESHOLD=0.75V  24000.  i i i i i i i i I i i i i i i i i i  10. D  MULTIPLICITY THRESHOLD^1. 5V  M u l t i p l i c i t y (number o f s t r i p s d i s c r i m i n a t o r t h r e s h o l d s . Only kept as good e v e n t s .  0.  }  TI  1  1  I  1  i  i i i.  I I l I I I I I I I I I I  5.0  10.0  MULTIPLICITY THRESHOLD=2.0V  f i r e d per event) f o r d i f f e r e n t s i n g l e s and some d o u b l e s a r e  FIGURE 4.14  128NeV/c  1  PARTICLES  1  0.0  0.5  1. 0  DISCRIMINATOR  Detector Net d a t a hits.  i 1. 5  ( 9 3 % PIONS)  i 2.0  i 2.5  THRESHOLD ( V ) '  e f f i c i e n c y a n d n o i s e f o r a -32V b i a s v o l t a g e . i n c l u d e s o n l y s i n g l e o r a d j a c e n t d o u b l e SS d e t e c t o r  FIGURE 4.15  Distribution pions.  o f l a b a n g l e o f muons  from decay  of 50MeV  FIGURE 4.16  3600.  —  I2O0.  —  ANGLE I  1600.  —  800.  —  0  40  ANGLE  60.  (mRADIANS) i  I  8b  (ALL EVENTS)  i i i i i i i i i  I  II  n 1111111 n 111111111 IT=T  (mRADIANS)  120  n 1 1 1 1 1 1 1 I I ] 1111 160  (DETECTOR  2D0  HITS)  —  0  4b  ANGLE  Bb  (mRADIANS)  120  160  200  (NOISE HITS)  A n g l e o f p a r t i c l e r a y t h r o u g h a p p a r a t u s (beam c e n t r e l i n e d e f i n e d a s z e r o ) . N o t i c e c o r r e l a t i o n between n o i s e s i g n a l s and a n g l e ; t h i s c o r r e l a t i o n i s c a u s e d by p i o n t o muon d e c a y i n t h e a p a r a t u s .  chamber, in  Figure  wire pion A  the  4.15  (REF  11).  but  due  chambers path,  3-4%  to  distribution  an  erroneous  traceback  ir t o  i n the  correlation  between  correlation  supports  Beam t e s t , The  product  t o the  of  and the  detector  represented  graphically in Figures  of  the  detection  The  efficiency  also  minimum  ionizing  amount  of  it  designed  increase  noise)  in  p e r f o r m a n c e of current.  with  increases  and for  only (70%  detector  Excess  b o t h of  these  several  times the  noise  strips  was were  average  due  shows  the  and  noise.  This  at  three  measured of  with  fixed  expected,  little 50% use  low  net  be  as  would  detected to  the  bias use  on  /xA/cm ). 2  efficiency loss.  voltage.  In  for detecting  50  MeV  noise). A to  17  large pions further  improve  increase  strips  have  polarity  efficient,  likely  is only  energy  f o r the  would not this  input  particle  increased  than  ( = 10-20  results  t o the  i s of  seen  the  Unfortunately,  efficient,  the  data  hypothesis.  was  of m a r g i n a l  voltage  test  cases.  4.16  path  increased  (less  bias  original  4.17.  was  detector  electrons  pion  Figure  summary  used due  improves  range t e s t e d , the  was  be  A  2735A d i s c r i m i n a t o r s . As  for  the  voltages.  could  the  the  efficiency  bias  biases  i n the  traceback  different  negative  to  in  i s c a l c u l a t e d i n most  TI t o u n o i s e  the  i s shown  detected  non-zero angle  apparatus.  angle  muon a n g l e  muons a r e  i s expected  test  of  resulting  traceback  bias voltage  efficiency  the  The  "noise"  (i d e c a y  of  and  leakage  the  leakage 23,  and  currents  FIGURE 4.17a  96MeV/c 100 -LU CO  o  9  8  I  PIONS:  DELTR  I  I  E 190KeV  "  0  25V  Bins  32V  Bins  39V  Bins  • EFFICIENCY D NOISE  "  0  L  70 O  60 -  LU  M (_)  50 -  U_ Ll_  40 -  W  3 0 -  — I W  20 -  «  10 -  4  0  0. 0  1 0.5  1  DISCRIMINATOR 128MeV/c  1  1.0  1. 5  THRESHOLD  PIONS:  DELTA  T— 2.0  2.5  ( V) E 150KeV  100 25V  UJ co o  so H 8  (  H  Bins  32V  Bins  39V  Bins  •  EFFICIENCY  a  NOISE  70 O  60  LU I—I  50  o  £ Ll_ LU LU  H H  40 30 20 10 0 0. 0  0.5  —r~ 1. 0 1.0  DISCRIMINATOR  —r~ 1.5 1.5  2.0  2.5  THRESHOLD (V)  Summary o f SS d e t e c t o r e f f i c i e n c i e s a n d n o i s e f o r v a r i o u s d e p o s i t e d e n e r g i e s , b i a s v o l t a g e and d i s c r i m i n a t o r t h r e s h o l d s , Only s i n g l e o r adjacent double h i t s a r e i n c l u d e d . See a l s o f i g u r e 4 . 1 7 b .  69  FIGURE 4 . 1 7 b  128MeV/c i  100 LU  MUONS:  DELTA E -1 1 OKeV  i 25V BIBS 32V BIBS  9°  39V BIBS  CO •  EFFICIENCY  •  NOISE  70 (_)  60  -  50 40 LU  2  **  30  -  20  -  10  -  0.0  1 0. 5  1 1.0  r~  1 1.5  2. 5  2.0  D I S C R I M I N A T O R THRESHOLD ( V)  128MeV/c  UJ CO  90  i  1  100  ELECTRONS:  DELTA E 86KeV  i 2SV BIBS 32V  H • •  70  -  60  H  50  H  40  -  30  -  20  -  >-* CJ LU  H  CJ  LU  BIBS  39V BIBS EFFICIENCY NOISE  •  10 0  0.0  1 0.5  1 1. 0  DISCRIMINATOR  SS d e t e c t o r  1 1.5  1— 2.0  THRESHOLD ( V)  efficiencies  and n o i s e .  2. 5  Timing  o f SS d e t e c t o r  Timing  signals  information  Discriminated  signals  available  using  These  by  signals  converter) for  started  one s t r i p  time over (time  seen  strips  strip  ECL/NIM/ECL in  a  in Figure  was  detector  converter TDC  recorded. were  made  (Figure 4.7).  (time  by t h e two s c i n t i l l a t o r s .  only  random  spectrum At  low  by 43 ns  i n t h e time  10  to  digital  A time  spectrum  4.18. Even w i t h  ns.  to the m a j o r i t y  reducing  time  detector..  separated  was  gate  40 n s , t h u s  the  the  recorded  i s shown  jitter)  The  some  the p r i m i t i v e  t h r e s h o l d d i s c r i m i n a t i o n , t h e w i d t h o f t h e t i m e peak  acquisition at  from an  were  for  The logic  width unit  could  the then  data be s e t  noise.  a l s o showed e v i d e n c e discriminator  (characteristic  spectrum.  of  of RF p i c k u p  settings,  noise  by  peaks  of t h e c y c l o t r o n ) c o u l d  be  FIGURE  '  240.  H  160.  H  i  i  i  i  i  i  i  i  I i  i  i  i  i  i  i  i  i  I i  i  i  i  4.18  i  i i  i i  I  I  I i i i t  80.  r r v v vr vr Tr r r r r V V V V T  80)  TIME  160  i  v v v •[' v \  (250ps/bin)  240  i'  vvvvvyvvvvvvvvvyv 320  400  i  DISCRIMINATOR THRESHOLD*0.75V  • i i i i i i i i i i i i i i i i i  ' •' 180.  •i  i  i i i i i i i i i  i  i i ii  H  1 20. —\  60.  H  I I I 1 I l"l T I I I I I  TIME  n  I I I I I i^V*rf 1 T I I T I I T I I I I I T I T T T I I I I T T I 160 240 320 400  (250ps/bin)  Time s p e c t r u m o f s i g n a l s noise i s c l e a r l y v i s i b l e period.  DISCRIMINATOR THRESHOLDS.25V  from one s t r i p . At low t h r e s h o l d w i t h a component h a v i n g a 43ns  CHAPTER V  SUMMARY AND CONCLUSION A  surface  developed MeV  solid  a t TRIUMF s p e c i f i c a l l y  pions  detector  barrier  at  high  fluxes.  The r a t e c a p a b i l i t y  e x c e s s o f 1 MHz p e r s t r i p  the  30  ns.  device  resolution scattering detector thinner  The e f f i c i e n c y  of the d e v i c e  f o r beam  and t a r g e t  could  of the prototype  i s expected  and e n e r g y  detectors  profile  p o s i t i o n monitor  a t low  t o be i n  signal  monitor,  length  active  a p p l i c a t i o n s i n the  would be more d e s i r e a b l e  be a c h i e v e d  i f  postion  i n b o t h d i r e c t i o n s . The m u l t i p l e  straggle associated  i s acceptable  with  the  55  for the a p p l i c a t i o n s proposed  mg/cm  2  although  would a l s o be d e s i r e a b l e .  improvements  The  low  efficiency  crystal,  signal  to  noise  of the prototype  sources.  There  leakage  of the prototype  work must be done  ratio  detector  pickup,  current  i n the s o l i d  noise  resulting  low  from t h e  detector  and e l e c t r o n i c s n o i s e .  noise  detector.  and  i s due t o one o r more o f  i s the i n t r i n s i c  RF e l e c t r o - m a g n e t i c  Excessive strips  was  f o r p o s i t i o n r e s o l u t i o n o f 50  as the c h a r a c t e r i s t i c  adequate  Ml 3 b e a m l i n e . The d e v i c e  three  system  The 1 mm r e s o l u t i o n and 40 mm a c t i v e d i a m e t e r o f  are  momentum s l i t ,  Noise,  detector  s y s t e m was measured a t 70% f o r t h e s e p a r t i c l e s  rates.  was  state  was  observed  on  two  To remedy t h i s p r o b l e m , more  state  laboratory. A l l that  may  be  necessary  wafers  the  t o smooth out  fabrication from  is  run  manufacture  problems with  processes,  t o run  and  the  the  best  of  s e v e r a l more  cleanliness.  quality devices  of  the  As  product  must be  chosen  detector with  all  will  vary  f o r use  as  detectors. The  strips  of  the  ambient  RF  power.  detector  was  s m a l l as  and  grounded.  SS  The  pickup  the  To  detector  reduce  system  should  with  inside  the  Electronics the  prototype  application the  noise  output  same s i z e The  of of  as  On  bias voltage  beam  most  noise and  they  output  of  may  Higher  discriminator  Newmarket  the  and  the  in a Faraday  biggest  the  cage  problem  detector  i n c r e a s e the n o i s e was  from minimum  low  hybrids  electronics. in  u s e f u l for measuring  detector.  shielded  noise seen  ionizing  ( a t which p o i n t  noise  are  combination  being  These  seen  t o be  England, the  energy  on the  particles. very  close  oscillation the  preamplifier  considered  devices,  in  strips,  a l s o have c o n t r i b u t e d a p o r t i o n of  gain  Microsystems  unshielded  problem,  a m p l i f i e r d i s c r i m i n a t o r s were o p e r a t e d  signals.  generation  the  of  d i d not  expected  this  for  pipe.  t o be  t o t h e minimum t h r e s h o l d p o s s i b l e occurs),  aerial  f o r the  operate  preamplifiers. This  pulse  LeCroy  appeared  system.  the  an  e l e c t r o n i c s were c a r e f u l l y  further  windows, or  as  observed  detector/preamplifier foil  act  f o r the  available  also  have  loss  of  an  next from  analogue  particles  in  Future  considerations  In  the  continue  immediate  on d e v i c e s  future  similar  d e t e c t o r . Two d i m e n s i o n a l problems device  stemming  from  The  of  t h e asymmetry  next  to noise  step  ratio  development  non-integrated  resolution devices observed  prototype  a r e p o s s i b l e , but i n the prototype  d e t e c t o r s c a n a l s o be  of p o s i t i o n  be i n t e g r a t i o n o f t h e  sensitive  first  stage  a m p l i f i c a t i o n on t h e same w a f e r a s t h e d e t e c t o r . T h i s  of  diameter  be a c c o m p l i s h e d solid  with  GaAs  state detectors w i l l  w a f e r s now  available.  will  i s increased.  i n the development  state detectors w i l l  probably size  the  TRIUMF,  may have t o be overcome. T h i n n e r  made i f t h e s i g n a l  solid  to  at  technology. soon expand  The  will  maximum  to the 8  inch  75  REFERENCES  1 (a) (b)  E . E . H a l l e r , H.W,Kramer, W.A.Higinbothom, Mat.Res.Soc. V o l 16, " N u c l e a r R a d i a t i o n D e t e c t o r M a t e r i a l s " , H o l l a n d Press J.H.Howes, J . W a t l i n g , P207 A.Musa, J.P.Ponpon, M . H a g e - A l i , P225  2  E.M.Lawson, N u c . I n s t . M e t h .  3  J.B.A.England, Physics", Part  4  A.A.Konova, N u c . I n s t . M e t h .  5  J.B.A.England  6  J.Kemmer e t a l , N u c . I n s t . M e t h .  7  W.J.Price, "Nuclear e d i t i o n , McGraw H i l l  8  S.M.Sze, and Sons  9  P.Borgeaud e t a l , "The E f f e c t of R a d i a t i o n on t h e Energy R e s o l u t i o n of Ion Implanted S i l i c o n Detectors", Commissariat a l'Energie Atomique Centre d'Etudes N u c l e a i r e s de S a c l a y , F r a n c e  10  J . B . A . E n g l a n d , V.W.Hammer, Nuc ..I n s t .Meth.  11  R.  12  J.B.A.England,  13  J.Yah-Min L e e , I E E E T r a n s a c t i o n s Vol.ED-28,No.4, A p r i l 1981  on  14  P.Janega,  May 1983  "Techniques in 1, M a c m i l l a n P r e s s  Nuclear  Private  Private  Radiation  196(1982)149  205(1983)99 Detection",  of S e m i c o n d u c t o r D e v i c e s " ,  Phd T h e s i s ,  Struture  160(1979)115  e t a l , Nuc.Inst.Meth.  "Physics  Tacik,  180(1981)651  second  John W i l e y  96(1971)81  UBC 1984 communication,  communication,  Dec 1984 Electron  Devices,  APPENDIX A MODIFIED Start both  with high sides,  Clean in  ENGLAND PROCESS  should  in solvent  and  utensils  BARRIER  wafers:  lifetime  ^3  with  must  DETECTORS  silicon  (2-Propanol,  d e i o n i z e d water  ms.  A c e t o n e ) and  ultrasound.  be  polished  very  then  ( A l l wet  c l e a n , a l l water  be d i s t i l l e d d e i o n i z e d ) .  the s l i c e  minutes. Boil  n"  - 5000 ficm, c a r r i e r  distilled  Boil  resistivity  the s l i c e  chemicals  FOR SURFACE  gently  Dilute  in  in concentrated n i t r i c  and d e c a n t  water  acid  for  5  with d i s t i l l e d d e i o n i z e d water.  f o r 5 minutes,  dilute  and d e c a n t  with  cold  (40%  HF:  water. Etch  the  wafer,  concentrated The  in  acetic  room  acid:  temperature  concentrated n i t r i c  w a f e r must be c o n s t a n t l y a g i t a t e d  "rippled" (per  surface  side).  wafer  2  acid/3:3:5).  and t e n d s  t o form  anyway. CP4A e t c h e s a t about  At l e a s t  i n H 0.  CP4A  10 Mm s h o u l d be removed.  Dilute  and d e c a n t  w i t h water  a  20 jim/min  Quench  the  (50% d i l u t i o n ,  5 times). Oxidize Place  the wafer it  minutes,  in  Dry  and can  in N  2  o  potassium  solution  be  dicromate  and h e a t  decant.  lamp, one may  the s l i c e  Evaporate  1%  the c o l d  dilute  contamination infra-red  in  observed  At as  want t o s t a r t  and p l a c e  solution.  t o 80 C, w a i t  this  point,  streaks  under  10 if an  over.  i n evaporator.  560-750 A o f Germanium  (p  doped  semiconductor  grade onto and  Ge  was  both  used  s i d e s of  p a s s i v a t e d by  with a s t a r t i n g the  the  silicon,  Evaporate patterns  210  A Au  or  a r e made on  the  surface  ground  1100  one  A A l onto  (start  plane  "ramp" w i t h T r a n s e n e and  through  a  to  epoxy  evaporate shadow  50  at  the  (Epotek  contacts  mask  to  (Figure  traces  must  be p r o b e d  with a p e n c i l  layer  very quickly  aluminum  aluminum in a i r .  shadow  mask  Torr pressure). board  H44).  mounting  Make an  strips  the  3.3).  gold. Often  if  6  Strip  epo.xy  ( o r CIBA AY105:HY956, 6:1  s h o u l d be  e v a p o r a t i o n s . The  Torr) formed  surfaces.  circuit  board  contact  both  10~  circuit  electrical  now  s u r f a c e with a wire  w i t h c o n d u c t i n g epoxy  weight)  is  6  o  i n c o n t a c t w i t h the wafer 10. G l u e  the diode  10~  Ge.  o  9.  p r e s s u r e of  is  circuit  The  point used  form an  board  traces  the e v a p o r a t e d  by  on  the  contact  t o make a good for  the  insulating  metal oxide  

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