UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Ion implanted GaAs Mesfet technology Lowe, Kerry Steven 1983

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

Item Metadata

Download

Media
831-UBC_1983_A7 L68.pdf [ 4.4MB ]
Metadata
JSON: 831-1.0095775.json
JSON-LD: 831-1.0095775-ld.json
RDF/XML (Pretty): 831-1.0095775-rdf.xml
RDF/JSON: 831-1.0095775-rdf.json
Turtle: 831-1.0095775-turtle.txt
N-Triples: 831-1.0095775-rdf-ntriples.txt
Original Record: 831-1.0095775-source.json
Full Text
831-1.0095775-fulltext.txt
Citation
831-1.0095775.ris

Full Text

ION  IMPLANTED GaAs MESFET TECHNOLOGY  by  KERRY STEVEN LOWE B . A . S c , The U n i v e r s i t y of B r i t i s h Columbia, 1981  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in THE FACULTY OF GRADUATE STUDIES i n the Department of Electrical  We accept t h i s  Engineering  t h e s i s as conforming  to the r e q u i r e d  standard  THE UNIVERSITY OF BRITISH COLUMBIA August 1983 ® K e r r y Steven Lowe , 1983  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 the head o f my department o r by h i s o r her r e p r e s e n t a t i v e s .  It is  understood t h a t copying or 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 not be allowed without my  permission.  Department o f  E/ecfnca  The U n i v e r s i t y of B r i t i s h 1956 Main Mall Vancouver, Canada V6T 1Y3 Date  I  Engineering  Columbia  written  ABSTRACT  The  a v a i l a b i l i t y of h i g h q u a l i t y s e m i - i n s u l a t i n g GaAs s u b s t r a t e s i s  e s s e n t i a l to the development of GaAs m e t a l semiconductor f i e l d e f f e c t t r a n s i s t o r (MESFET) i n t e g r a t e d c i r c u i t s . h o r i z o n t a l Bridgman grown s u b s t r a t e s  s i n c e , f o r example, these must be doped  w i t h Cr to make then s e m i - i n s u l a t i n g and device processing.  Problems have been encountered w i t h  the Cr tends t o d i f f u s e d u r i n g  Undoped s e m i - i n s u l a t i n g GaAs s u b s t r a t e s  the L i q u i d E n c a p s u l a t e d C z o c h r a l s k i (LEC)  t e c h n i q u e and  can be grown by  a l l o w the  possibility  of f o r m i n g a c t i v e r e g i o n s by the process of i m p l a n t i n g dopants d i r e c t l y i n t o the  substrate. The  purpose of t h i s t h e s i s was  t o develop at the U n i v e r s i t y of  Columbia a GaAs MESFET t e c h n o l o g y based on d i r e c t i o n i m p l a n t a t i o n and develop methods to a s s e s s undoped LEC B.C. device  substrates  f o r Cominco L i m i t e d ,  A t e s t d e v i c e a r r a y c o n s i s t i n g of s t r u c t u r e s f o r p r o c e s s , c h a r a c t e r i z a t i o n was  designed and  a d i r e c t implantation process.  British to Trail,  material,  and  then f a b r i c a t e d on Cominco w a f e r s by  Measurements on the t e s t d e v i c e  array  elements showed t h a t t h i s i n i t i a l process c o u l d be used t o produce MESFET's o p e r a t i o n a l up t o 3." GHz monitoring  and  t h a t the t e s t d e v i c e a r r a y w i l l be u s e f u l f o r  f u t u r e p r o c e s s developments and  improvements.  In a d d i t i o n , a  channel conductance deep l e v e l t r a n s i e n t s p e c t r o s c o p y system, a p h o t o c u r r e n t deep l e v e l t r a n s i e n t s p e c t r o s c o p y system, and a n o v e l MESFET d r a i n  current  h y s t e r e s i s a n a l y s i s system were developed to examine deep l e v e l s i n GaAs and deep l e v e l t r a p p i n g e f f e c t s i n GaAs MESFET's.  ii  TABLE OF CONTENTS Page ABSTRACT  i i  LIST OF TABLES  v  LIST OF FIGURES  vi  ACKNOWLEDGEMENTS  viii  1.  INTRODUCTION  1  2.  OVERVIEW OF GaAs MESFET TECHNOLOGY  3  2.1 2.2 2.3  Introduction Device Considerations Substrate Considerations  3 3 6  2.4  Process C o n s i d e r a t i o n s  8  3.  THE TEST DEVICE ARRAY 3.1 3.2  4.  5.  9  Description Fabrication 3.2.1 Substrate Preparation 3.2.2 S e l e c t i v e Ion I m p l a n t a t i o n 3.2.3 Post Implant Anneal 3.2.4 M e t a l l i z a t i o n  9 13 13 14 15 15  MEASUREMENTS ON THE TEST DEVICE ARRAY  21  4.1 4.2 4.3  A c t i v e Layer E v a l u a t i o n Gate M e t a l l i z a t i o n E v a l u a t i o n Ohmic Contact M e t a l l i z a t i o n E v a l u a t i o n  21 31 35  4.4  MESFET E v a l u a t i o n  35  DEEP LEVEL TRANSIENT SPECTROSCOPY (DLTS)  40  5.1 5.2 5.3 5.4  40 43 50 53  Basic P r i n c i p l e s Channel Conductance DLTS P h o t o c u r r e n t DLTS Measurements  iii  Page 6.  7.  HYSTERESIS-FREQUENCY  SPECTROSCOPY  66  6.1 6.2  Theory Apparatus  66 73  6.3  Measurements  75  SUMMARY AND CONCLUSION  79  REFERENCES  81  APPENDIX A  S u b s t r a t e Compensation C o n s i d e r a t i o n s  85  APPENDIX B  Some Ion I m p l a n t a t i o n Processes Used f o r GaAs MESFET F a b r i c a t i o n Some Deep L e v e l s i n GaAs Detected by DLTS  88  APPENDIX C  iv  89  LIST OF TABLES Page 3.1  Test d e v i c e a r r a y s t r u c t u r e s  9  4.1  Active layer properties  30  4.2  M e t a l l i z a t i o n properties  33  4.3  MESFET y i e l d  36  4.4  Device parameters of 3 un MESFET's  39  5.1  Deep l e v e l s d e t e c t e d  54  5.2  P r o p e r t i e s of Cominco GaAs  60  5.3  Deep l e v e l s d e t e c t e d  64  by CDLTS  by PDLTS  v  LIST OF FIGURES Page 2.1  GaAs MESFET  4  2.2  Comparison of a c t i v e l a y e r f o r m a t i o n p r o c e s s e s  7  3.1  Layout of the t e s t d e v i c e a r r a y  11  3.2  The masks f o r the t e s t d e v i c e a r r a y  12  3.3  F a b r i c a t i o n sequence f o r the t e s t d e v i c e a r r a y  17  4.1  E x p e r i m e n t a l arrangement used f o r van der Pauw measurements ....  22  4.2  E x p e r i m e n t a l arrangement used f o r C-V measurements  24  4.3  E x p e r i m e n t a l arrangement used f o r d r i f t m o b i l i t y p r o f i l i n g  26  4.4  A c t i v e l a y e r sheet r e s i s t a n c e v a l u e s f o r wafer  27  sections fabricated 4.5  C-V p l o t f o r sample 123-S131(R1-C5)  28  4.6  C a r r i e r d e n s i t y and d r i f t m o b i l i t y p r o f i l e f o r sample 123-S131(R1-C5) Schottky diode c u r r e n t - v o l t a g e p l o t f o r sample 123-S131(R1-C5)  29  4.8  SEM photograph (2000x mag.) f o r 3 un MESFET sample 123-S131(R2-CS)  34  4.9  c h a r a c t e r i s t i c s f o r 3 un MESFET sample 123-S131(R1-C5)  37  4.10  IGS~ GS  c h a r a c t e r i s t i c s f o r 3 un MESFET  38  4.7  !DS~ DS V  V  32  sample 123-S131(R1-C5) 5.1  B a s i c p r i n c i p l e of DLTS t r a n s i e n t g e n e r a t i o n  42  5.2  B a s i c p r i n c i p l e of d u a l c h a n n e l boxcar s a m p l i n g of  43  DLTS t r a n s i e n t 5.3  B l o c k diagram of channel conductance DLTS arrangement  46  5.4  Sample h o l d e r used f o r DLTS measurements  47  vi  Page 5.5  B l o c k diagram of p h o t o c u r r e n t DLTS arrangement  52  5.6  A CDLTS spectrum f o r 3 um MESFET sample 123-S131(R1-C5)  55  5.7  A CDLTS spectrum f o r 3 um MESFET sample 43-S10(R2-C6)  56  5.8  A CDLTS spectrum f o r 3 um MESFET sample 51-T132(R1-C3)  57  5.9  A c t i v a t i o n energy p l o t f o r t r a p s d e t e c t e d by CDLTS  58  5.10  I - V c h a r a c t e r i s t i c s f o r 3 um MESFET sample 51-T132(R1-C3)  59  5.11  A PDLTS spectrum f o r sample 63-T42(A)  61  5.12  A PDLTS spectrum f o r sample 82-S14(A)  62  5.13  A c t i v a t i o n energy p l o t f o r t r a p s d e t e c t e d by PDLTS  63  5.14  Comparison of t r a p s i g n a t u r e s  65  6.1  I o n i z a t i o n of t r a p s i n t h e d e p l e t i o n r e g i o n due t o t h e sweep of gate v o l t a g e w i t h a sawtooth waveform  67  6.2  The d i f f e r e n c e (AL) between the n o r m a l i z e d d e p l e t i o n w i d t h .... when VQ changes from zero t o -1/2 V as a f u n c t i o n o f n o r m a l i z e d sweep f r e q u e n c y  72  6.3  E x p e r i m e n t a l arrangement f o r h y s t e r e s i s measurements  74  6.4  I - V c h a r a c t e r i s t i c s f o r MESFET 45-S93 (R4-C3)  76  6.5  H y s t e r e s i s s p e c t r a f o r MESFET 45-S93(R4-C3)  77  6.6  A c t i v a t i o n energy p l o t f o r MESFET 45-S93(R4-C3) as o b t a i n e d by h y s t e r e s i s and CDLTS measurements  78  M  vii  ACKNOWLEDGEMENTS  I would l i k e t o thank my s u p e r v i s o r , Dr. L. Young, f o r h i s guidance and encouragement d u r i n g t h e course of my work. I am g r a t e f u l t o Mr. J i L i j i u and Dr. W. Lau f o r t h e i r numerous h e l p f u l d i s c u s s i o n s and f o r t h e i r work on t h e h y s t e r e s i s  technique.  Dr. N. T a r r , now a t C a r l e t o n U n i v e r s i t y , Ottawa, i s thanked f o r h i s work on d e v i c e f a b r i c a t i o n and t h e DLTS system and Mr. D Hutcheon f o r ing  prepar-  t h e t e s t d e v i c e a r r a y masks. The  a s s i s t a n c e of Messrs. D. Madge and R. N o r t h of Optotek L i m i t e d ,  Ottawa i n i m p l a n t i n g the wafers i s a p p r e c i a t e d  as i s Mr. G. Needham o f  Cominco L i m i t e d , T r a i l , B.C., who s u p p l i e d t h e GaAs w a f e r s . S e v e r a l o t h e r s have a i d e d t h i s work and a r e acknowledged.  These  i n d i v i d u a l s i n c l u d e Drs. D. Smith, and R. Koyama, Mr. M. M a j o r , M e s s r s . F. B e r r y , A. Leugner, F. K s c h i s c h a n g , W. Tang, and F. Wan. I a l s o thank G a i l Schmidt f o r t y p i n g t h e m a n u s c r i p t and I am i n d e b t e d t o W. Tang f o r h i s a s s i s t a n c e i n p r e p a r i n g  the f i g u r e s .  F i n a n c i a l support was p r o v i d e d by t h e B r i t i s h and by NSERC.  viii  Columbia Science  Council  1  1.  INTRODUCTION  G a l l i u m a r s e n i d e m e t a l semiconductor f i e l d e f f e c t t r a n s i s t o r s (GaAs MESFET's) have shown c o n s i d e r a b l e  p o t e n t i a l f o r use i n h i g h speed d i g i t a l and  m o n o l i t h i c microwave i n t e g r a t e d c i r c u i t s ( I C ' s ) . and  For example, 8-12 GHz  three  f o u r stage a m p l i f i e r s have been i n t e g r a t e d (Wisseman e t a l . , 1983) and  l a r g e s c a l e (> 1 0  3  g a t e s ) d i g i t a l c i r c u i t s r e a l i z e d (Eden, 1981), but b e f o r e  such IC's can become c o m m e r c i a l l y v i a b l e and o t h e r s of g r e a t e r  complexity  d e v e l o p e d , improved s u b s t r a t e growth and d e v i c e f a b r i c a t i o n t e c h n i q u e s a r e required.  One GaAs MESFET process t e c h n o l o g y ( o t h e r s a r e d i c u s s e d  2) t h a t appears v e r y p r o m i s i n g  i n Chapter  i n v o l v e s the use of m u l t i p l e s e l e c t i v e i o n  i m p l a n t a t i o n d i r e c t l y i n t o undoped s e m i - i n s u l a t i n g GaAs s u b s t r a t e s grown by the L i q u i d E n c a p s u l a t e d C z o c h r a l s k i (LEC) method. The o b j e c t i v e s of t h i s t h e s i s were t o develop a t the U n i v e r s i t y of B r i t i s h Columbia a GaAs MESFET t e c h n o l o g y based on d i r e c t i o n i m p l a n t a t i o n and  i n c o n j u n c t i o n w i t h Cominco L i m i t e d , T r a i l , B.C. ( a s u p p l i e r of undoped  LEC s u b s t r a t e s ) device  to develop methods t o assess t h e i r GaAs f o r s u i t a b i l i t y i n  f a b r i c a t i o n . A t e s t d e v i c e a r r a y c o n s i s t i n g of s t r u c t u r e s f o r p r o -  c e s s , m a t e r i a l , and d e v i c e s t r a t e s were o b t a i n e d  c h a r a c t e r i z a t i o n was d e s i g n e d .  Undoped LEC sub-  from Cominco and used t o f a b r i c a t e the a r r a y by a  d i r e c t i o n implantation process.  Measurements were then performed on the  a r r a y elements t o a s s e s s the f a b r i c a t i o n s . To f u r t h e r a s s i s t i n m a t e r i a l and process development t h r e e  techniques  f o r c h a r a c t e r i z i n g deep l e v e l s i n GaAs were i n v e s t i g a t e d as deep l e v e l s p l a y an i m p o r t a n t r o l e i n s u b s t r a t e compensation (Appendix A) and can a l s o cause  2  degraded d e v i c e b e h a v i o u r .  The t h r e e techniques were channel  deep l e v e l t r a n s i e n t s p e c t r o s c o p y m a t e r i a l , photocurrent  conductance  f o r c h a r a c t e r i z i n g deep l e v e l s i n i m p l a n t e d  deep l e v e l t r a n s i e n t s p e c t r o s c o p y  for characterizing  deep l e v e l s i n s e m i - i n s u l a t i n g m a t e r i a l and a n o v e l t e c h n i q u e  f o r character-  i z i n g deep l e v e l s which cause t h e commonly observed e f f e c t of h y s t e r e s i s ( l o o p i n g ) i n GaAs MESFET I-V c h a r a c t e r i s t i c s . Chapter 2 g i v e s a b r i e f o v e r v i e w of GaAs MESFET t e c h n o l o g y . d e s c r i b e s the t e s t d e v i c e a r r a y and the d i r e c t i m p l a n t a t i o n process  Chapter 3 used i n  i t s f a b r i c a t i o n w h i l e Chapter 4 d e s c r i b e s the measurements performed t o assess  the f a b r i c a t i o n s .  Chapter 5 d e s c r i b e s the o p e r a t i o n of and measure-  ments performed w i t h the DLTS systems and Chapter 6 t h e o p e r a t i o n of and measurements performed w i t h t h e h y s t e r e s i s a n a l y s i s system. the summary and c o n c l u s i o n s of t h i s  thesis.  Chapter 7 g i v e s  3  2.  2.1  OVERVIEW OF GaAs MESFET TECHNOLOGY  Introduction I n t e g r a t e d c i r c u i t s capable of o p e r a t i n g at speeds i n excess of 1 GHz  are needed i n microwave communication  systems, h i g h speed computers,  f i b r e systems, and h i g h speed t e s t equipment.  optical  I t i s becoming i n c r e a s i n g l y  d i f f i c u l t t o e x t r a c t more speed from S i d e v i c e s and i t i s d o u b t f u l whether S i IC's can s a t i s f y these needs. speed advantage  GaAs IC's have a two t o s i x times p o t e n t i a l  over S i IC's due i n p a r t t o GaAs's h i g h e r e l e c t r o n m o b i l i t y .  Furthermore, s i n c e GaAs s u b s t r a t e s may be grown i n a s e m i - i n s u l a t i n g s t a t e w i t h r e s i s t i v i t y near 1 0  8  ten (compared w i t h a t h e o r e t i c a l 1 0  5  tan f o r S i )  and the GaAs r e t a i n s i t s h i g h r e s i s t i v i t y a f t e r d e v i c e p r o c e s s i n g , GaAs IC's can have l o w i n t e r - d e v i c e p a r a s i t i c c a p a c i t a n c e s and s i m p l e i n t e r - d e v i c e isolation  2.2  structure.  Device C o n s i d e r a t i o n s GaAs MESFET's were proposed by Mead (1966) and f i r s t r e a l i z e d by  Hooper and L e h r e r (1967). IC's.  They a r e the most w i d e l y used t r a n s i s t o r i n GaAs  (Other c h o i c e s i n c l u d e j u n c t i o n f i e l d e f f e c t t r a n s i s t o r s (JFET's) and  m e t a l i n s u l a t o r f i e l d e f f e c t t r a n s i s t o r s (MISFET's)).  The b a s i c s t r u c t u r e of  a GaAs MESFET c o n s i s t s of an n-type channel on a s e m i - i n s u l a t i n g GaAs s u b s t r a t e , source and d r a i n ohmic c o n t a c t s and a m e t a l gate c o n t a c t which forms a S c h o t t k y j u n c t i o n w i t h the channel ( F i g . 2.1). The gate t o source v o l t a g e governs the depth of the gate d e p l e t i o n r e g i o n and hence t h e conductance  of the c h a n n e l .  As the gate v o l t a g e i s d e c r e a s e d , t h e d e p l e t i o n  F i g . 2.1  GaAs MESFET  5  r e g i o n expands and the channel conductance channel becomes p i n c h e d - o f f .  i s reduced u n t i l e v e n t u a l l y the  The maximum v o l t a g e on the gate ( w i t h r e s p e c t  t o the s o u r c e ) r e q u i r e d t o cause p i n c h - o f f i s c a l l e d t h e t h r e s h o l d v o l t a g e V^, and i s n e g a t i v e f o r a d e p l e t i o n ( n o r m a l l y on) MESFET and p o s i t i v e f o r an enhancement ( n o r m a l l y o f f ) MESFET. The f i r s t GaAs MESFET IC was r e p o r t e d by Van T u y l and L i e c h t i (1974). The c i r c u i t was a NAND/NOR l o g i c gate and i t o p e r a t e d t h r e e times f a s t e r than the f a s t e s t S i l o g i c gate ( a t t h a t time) thus d e m o n s t r a t i n g the h i g h speed p o t e n t i a l of GaAs I C ' s . The s t r u c t u r e and o p e r a t i o n of a GaAs JFET i s - s i m i l a r t o t h a t of the MESFET except t h a t i n a JFET a p n j u n c t i o n gate i s used. +  MESFET's have been  p r e f e r r e d over JFET's because JFET's have a l a r g e r gate sheet r e s i s t a n c e and a r e more d i f f i c u l t t o f a b r i c a t e .  S i n c e the f i r s t GaAs JFET IC was r e p o r t e d  by N o t t h o f f and Zuleeg (1975), o n l y r e l a t i v e l y c o a r s e gate l e n g t h JFET IC's have been r e p o r t e d ( i . e . 1.3 ym by Kato e t a l . , 1981) w h i l e 0.5 um gate l e n g t h MESFET IC's have been f a b r i c a t e d (Barna and L i e c h t i , 1979, Yamasaki et a l . , 1982).  JFET's have a h i g h e r gate t o channel b u i l t - i n v o l t a g e than  MESFET*s ( t y p i c a l l y 1.4 V f o r JFET's t o 0.8 V f o r MESFET's) and so (Lehovec and Z u l e e g , 1980) can accommodate a l a r g e r f o r w a r d b i a s and thus i n d i g i t a l c i r c u i t s permit a l a r g e r l o g i c v o l t a g e swing and n o i s e margin, but a g a i n as p o i n t e d out by Lehovec and Zuleeg (1980) t h i s advantage  of JFET's over  MESFET's w i l l d i s a p p e a r i f power s u p p l y l e v e l s i n d i g i t a l c i r c u i t s a r e below 0.7 V as w i l l be r e q u i r e d f o r u l t r a - l a r g e s c a l e ( > 1 0 g a t e s ) c i r c u i t s . 5  MISFET's have an i n s u l a t i n g f i l m between the gate and c h a n n e l .  GaAs  The i n s u l a t o r  must g i v e good i s o l a t i o n , low s u r f a c e s t a t e d e n s i t y , and l o n g term d e v i c e  6  stability.  S e v e r a l d i e l e c t r i c s have been t r i e d , as reviewed by Boyd  (1981),  but a s a t i s f a c t o r y i n s u l a t o r has not been found.  2.3  Substrate Considerations S e m i - i n s u l a t i n g GaAs s u b s t r a t e s have been grown by the h o r i z o n t a l  Bridgman technique s i n c e the e a r l y 1960's.  GaAs i s s y n t h e s i z e d i n a q u a r t z  boat w i t h e l e m e n t a l Ga and As vapour i n s i d e a f u r n a c e . cooled by s l o w l y moving the boat away from the f u r n a c e . is  added to the melt.  The GaAs melt i s then P r i o r to c o o l i n g Cr  The Cr i n t r o d u c e s a deep l e v e l i n GaAs which  sates the s h a l l o w i m p u r i t i e s found to contaminate  the melt  compen-  ( M a r t i n et a l . ,  1980). In the LEC s u b s t r a t e growth technique a GaAs melt i s c o n t a i n e d i n a quartz or p y r o l i t i c boron n i t r i d e w i t h B^Oj-  (PBN)  crucible.  The melt i s e n c a p s u l a t e d  To grow a GaAs i n g o t a seed i s immersed i n t o and then s l o w l y  p u l l e d from the m e l t .  The LEC technique was  by Metz et a l . (1962) but commercial r e c e n t l y been a v a i l a b l e  used more than twenty years  ago  LEC c r y s t a l growth equipment has o n l y  (1979).  An a t t r a c t i v e f e a t u r e of the LEC method i s that round wafers are p r o duced  compared to the D shaped wafers produced  by the Bridgman method.  second f e a t u r e of the LEC method i s that s e m i - i n s u l a t i n g wafers may d u c i b l y a t t a i n e d without the need  be r e p r o -  f o r i n t e n t i o n a l Cr doping as s h a l l o w  i m p u r i t i e s i n t h i s m a t e r i a l are compensated v i a an i n t r i n s i c deep l e v e l formed  d u r i n g c r y s t a l growth (Appendix A ) .  A  n -epi SI  (a)  GaAs  n -eP' / / / / / epi-buffer / / / / / / (b) SI  GaAs  ~p _ n_- implant \/ / 7 / / / epi-buffer// / / / / SI  GaAs  n j_irnplant _ SI  (C)  _ _ j  GaAs  F.ig. 2.2 Comparison o f a c t i v e l a y e r f o r m a t i o n processes (a) E p i t a x i a l growth (b) E p i t a x i a l growth on b u f f e r l a y e r (c) Implantation i n t o buffer layer (d) D i r e c t i o n i m p l a n t a t i o n  8  2.4  Process  Considerations  D i f f i c u l t i e s encountered w i t h Bridgman s u b s t r a t e s  (such as the d e g r a d -  a t i o n of a c t i v e l a y e r p r o p e r t i e s due t o Cr i m p u r i t y d i f f u s i o n , Udagawa et a l . , 1980) l e a d t o the development of GaAs MESFET f a b r i c a t i o n p r o c e s s e s i n which h i g h r e s i s t i v i t y e p i t a x i a l b u f f e r l a y e r s a r e grown on a s u b s t r a t e and a c t i v e l a y e r s formed by a second e p i t a x i a l growth ( F i g . 2.2b) o r by i o n i m p l a n t a t i o n i n t o t h e b u f f e r l a y e r ( F i g . 2.2c).  With LEC substrate's, how-  e v e r , a c t i v e l a y e r f o r m a t i o n by d i r e c t i o n i m p l a n t a t i o n ( F i g . 2.2c) appears p o s s i b l e (Welch e t a l . , 1980). A t t r a c t i v e f e a t u r e s of d i r e c t i o n i m p l a n t a t i o n i n c l u d e : h i g h t h r o u g h put (no e p i t a x i a l growth r e q u i r e d ) , the f a c t t h a t s e l e c t i v e i m p l a n t a t i o n may be performed ( i n which o n l y c e r t a i n p a r t s of a wafer a r e i m p l a n t e d ) a l l e v i a t i n g the need f o r i n t e r - d e v i c e i s o l a t i o n procedures ("planar" and  technology),  the f a c t t h a t m u l t i p l e and m u l t i p l e s e l e c t i v e i m p l a n t a t i o n s may be p e r -  formed.  Recently  Appendix B.  r e p o r t e d d i r e c t i m p l a n t a t i o n p r o c e s s e s a r e summarized i n  9  3.  3.1  THE  TEST DEVICE ARRAY  Description A t e s t d e v i c e a r r a y designed  f o r use  i n e v a l u a t i n g GaAs i n t e g r a t e d  c i r c u i t p r o c e s s i n g and m a t e r i a l p r o p e r t i e s i s i l l u s t r a t e d i n F i g . Included  i n the a r r a y , which i s p a r t l y based on t h a t of Immorlica et a l .  (1980), are a Schottky  diode  cross s t r u c t u r e s f o r use  f o r c a r r i e r d e n s i t y p r o f i l i n g , van der Pauw  i n H a l l e f f e c t measurements, (David and  1977), a long gate MESFET ("fat FET") checking  s u b s t r a t e i s o l a t i o n and  um)  f o r use  STRUCTURE  resistance, a structure for  a set of narrow gate l e n g t h MESFET's ( 1 -  i n device c h a r a c t e r i z a t i o n (Table  Table  3.1  - Test Device A r r a y  PURPOSE  NAME  1  Schottky  2  Substrate t i o n pads  diode  Buehler,  f o r d r i f t m o b i l i t y p r o f i l i n g , pads f o r  ohmic contact  measuring gate metal r e s i s t a n c e , and 10  3.1.  n-implant c a r r i e r density p r o f i l i n g  i s o l a - Test of s u b s t r a t e isolation  3.1).  Structures  DESCRIPTION Gate dimension=100x200  um  (Ohmic) metal pads on SI s u b s t r a t e Pad dimension=100xl00 um Pad separations=40,20,10  3  van der Pauw cross  Measurement of H a l l m o b i l i t y and sheet r e s i s t a n c e of n-implant  Length of cross=200 um Width of cross=40 um  4  van der Pauw cross  Measurement of H a l l m o b i l i t y and sheet r e s i s t a n c e of n -implant  Length of cross=250 Width of cross=40  um  m  u  um  +  ...continued  10  STRUCTURE 5  Ohmic pads  6  7 ,8  9  PURPOSE  NAME contact  DESCRIPTION  Measurement o f ohmic c o n t a c t resistance  Ohmic m e t a l pads on i m p l a n t e d layer Pad dimension=100xl00 ym Pad separations=40,20,10,5 ym  Gate m e t a l structure  Measurement of gate m e t a l sheet resistance  Number of squares=50  S p l i t gate MESFET  Device tion  Fat FET  Drift mobility profiling  1 jjn MESFET  Device c h a r a c t e r i z a - Gate width=200 ym tion  C h a r a c t e r i z a - Gate length=4  Long gate MESFET Gate dimension=100x200 yea  ..  ..  ..  ..  ..  ..  ••  .,  ..  ..  ••  ••  10  2 ym  11  3 ym  12  4 ym  13  4 ym  14  6 ym  15  8 m  16  10 ym "  17  Dual gate MESFET  18  MIM c a p a c i t o r  19  Coarse r e g i s t r a - Mask alignment a i d t i o n mark  "  "  ym  ••  ••  ..  Gate length=4  ••  ym  Test o f d i e l e c t r i c properties  S i x masks were designed f o r use i n f a b r i c a t i n g the a r r a y v i a a multiple direct selective i o n implantation  approach ( r e g i s t r a t i o n e t c h mask,  F i g . 3.1  Layout o f t h e t e s t d e v i c e a r r a y  F i g . 3.2 The masks f o r t h e t e s t d e v i c e a r r a y (a) R e g i s t r a t i o n marks (d) Gate m e t a l (e) Ohmic c o n t a c t s ( f ) 2nd l a y e r m e t a l  (b) n - i m p l a n t  (c) n - i m p l a n t  13  n-implant mask, n i m p l a n t mask, ohmic c o n t a c t m e t a l l i z a t i o n mask, gate m e t a l +  l i z a t i o n mask, and second l e v e l m e t a l l i z a t i o n mask). d e s i g n s were e n t e r e d i n t o t h e U.B.C. Computing gram w r i t t e n by G. Cheng.  C e n t r e ' s Amdahl u s i n g a p r o -  The f i l e s were then downlinked t o a PDP8e i n t h e  E l e c t r i c a l E n g i n e e r i n g Department t h i s program.  To p r e p a r e t h e masks,  and a r u b y l i t h master c u t under c o n t r o l o f  The r u b y l i t h was sent t o P r e c i s i o n Photomask, Quebec, f o r  f a b r i c a t i o n of t h e p h o t o g r a p h i c ( s t e p p e d and r e p e a t e d ) masks.  To reduce p r o -  d u c t i o n c o s t s the r e q u i r e d s i x p a t t e r n were grouped i n t o two masks as shown i n F i g . 3.2. With t h i s arrangement  about 150 r e p l i c a t i o n s o f t h e  1.0 x 3.3 mm a r r a y can be made on a 50 mm diameter w a f e r .  3.2  Fabrication  3.2.1  Substrate Preparation S e m i - i n s u l a t i n g GaAs wafers were o b t a i n e d from Cominco L i m i t e d i n  o r d e r t o c a r r y out an i n i t i a l f a b r i c a t i o n r u n of the t e s t d e v i c e a r r a y . w a f e r s were LEC grown and undoped.  The  The d i a m e t e r of each wafer was 50 mm, t h e  t h i c k n e s s 0.50 mm, and the c r y s t a l o r i e n t a t i o n ( 1 0 0 ) . The p r o c e s s used t o f a b r i c a t e t h e w a f e r s began w i t h the f o l l o w i n g p r e c l e a n i n g procedure ( F i g . 3.3a). 1.  A t h r e e p a r t d e g r e a s i n g c o n s i s t i n g of a 5 minute t r i c h l o r e t h y l e n e b a t h , a 5 minute b o i l i n g acetone b a t h , and f i n a l l y a 5 minute b o i l i n g  isopropanol  bath. 2.  An e t c h t o remove any work damage i n t r o d u c e d d u r i n g w a f e r sawing and polishing.  The e t c h c o n s i s t e d of a 3 minute immersion i n  ilH^O^lH^rlH^  f o l l o w e d by a 10 minute DI water r i n s e .  14  3.  A n a t i v e o x i d e e t c h c o n s i s t i n g of a 10 minute immersion i n b o i l i n g c o n c e n t r a t e d HC1 f o l l o w e d by a 10 minute DI water r i n s e .  3.2.2  S e l e c t i v e Ion I m p l a n t a t i o n F o l l o w i n g c l e a n i n g , an S i O  the  f i l m of 0.6  A P e r k i n - E l m e r 3140 RF s p u t t e r i n g system was used w i t h an S i 0  2  The s p u t t e r i n g gases were A r , 34 m i l l i t o r r , and 0 , 4 m i l l i t o r r . 2  h e l p s p r e s e r v e the s t o i c h i o m e t r y of the f i l m s ) . the  ym t h i c k n e s s was d e p o s i t e d on  w a f e r s t o s e r v e as a mask i n the s e l e c t i v e i o n i m p l a n t a t i o n process ( F i g .  3.3b). get.  2  d e p o s i t i o n r a t e was found t o be about 0.15  tar(0  2  For a f o r w a r d power of 150 W ym/hr.  In the next p r o c e s s s t e p , windows were opened i n the S i 0  to permit  2  the  e t c h i n g of r e g i s t r a t i o n marks i n the s u b s t r a t e s ( F i g . 3.3c).  are  n e c e s s a r y i n o r d e r t o l o c a t e those r e g i o n s of the wafer which have been  implanted. 1.  The f o l l o w i n g procedure was  These marks  used:  A p h o t o r e s i s t procedure ( u s i n g the r e g i s t r a t i o n mark mask) c o n s i s t i n g of p h o t o r e s i s t d e p o s i t i o n ( S h i p l e y AZ1350J), a 30 minute 70° bake, mask alignment and exposure u s i n g a Kasper a l i g n e r , p h o t o r e s i s t development, 10 minute DI water r i n s e , and f i n a l l y a 60 minute 120°C bake.  2.  An SiO2 e t c h c o n s i s t i n g of a 5 minute immersion i n a b u f f e r e d o x i d e e t c h (NH^+HF) and an immersion i n acetone t o remove the p h o t o r e s i s t .  3.  A s u b s t r a t e e t c h c o n s i s t i n g of a 1 minute immersion i n 10% HC1, a 1 minute DI water r i n s e , a 50 s immersion i n 5% HgPO^ 2.5% H 0 2  a p p r o x i m a t e l y 0.1  2  ( t o remove  yn of the s u b s t r a t e ) , and a 5 minute DI water r i n s e .  Next, a second s e t of windows were opened i n the S i 0 r e g i o n s of the w a f e r s t o be i m p l a n t e d ( F i g . 3.3d).  2  t o d e f i n e the  T h i s was a c c o m p l i s h e d  a  15  u s i n g t h e p h o t o r e s i s t procedure ( w i t h the n-implant procedure d e s c r i b e d above. dose of 3 x l 0  1 2  cm  - 2  (Fig.  2 9  mask) and the S i 0  2  etch  S i was i m p l a n t e d a t an energy of 100 keV t o a  3.3e).  The i m p l a n t a t i o n s were done by Optotek  L i m i t e d , Ottawa, u s i n g an E x t r i o n 200 ( s i n c e f a c i l i t i e s were not y e t a v a i l a b l e a t U.B.C).  To reduce f a b r i c a t i o n time and c o m p l e x i t y n  and second l e v e l m e t a l l i z a t i o n were not done. reduce ohmic c o n t a c t r e s i s t a n c e .  +  implantations  ( n i m p l a n t a t i o n i s used t o +  Second l e v e l m e t a l l i z a t i o n i s used t o  a c h i e v e low r e s i s t a n c e i n t e r c o n n e c t s ) .  3.2.3  Post-Implant  Anneal  F o l l o w i n g i m p l a n t a t i o n the i m p l a n t mask was s t r i p p e d u s i n g a 10 minute buffered oxide etch.  An S i 0  2  l a y e r , 0.17  um t h i c k , was then d e p o s i t e d (by RF  s p u t t e r i n g ) t o serve as an anneal cap ( F i g . 3 . 3 f ) .  A n n e a l i n g was done i n a  M i n i B r u t e f u r n a c e i n t h e f o l l o w i n g manner: 1.  The f u r n a c e temperature was s e t to 850° and gas f l o w 14 l i t e r / m i n u t e N and 1 l i t e r / m i n u t e H  2  2  established.  2.  The wafers were p l a c e d a t t h e f r o n t of t h e f u r n a c e f o r 5 m i n u t e s .  3.  The wafers were p l a c e d a t c e n t e r of the f u r n a c e f o r 20 m i n u t e s .  4.  The w a f e r s were p l a c e d a t t h e f r o n t of the f u r n a c e f o r 5 minutes t o complete the a n n e a l .  The e n c a p s u l a n t  3.2.4  was then s t r i p p e d u s i n g b u f f e r e d o x i d e e t c h ( F i g . 3.3g).  Metallization In the next s t a g e , ohmic m e t a l l i z a t i o n , t h e s i n g l e s t e p  t e c h n i q u e of H a t z a k i s (1980) was used.  liftoff  The f o l l o w i n g s t e p s were performed:  16  1.  D e g r e a s i n g (as d e s c r i b e d i n S e c t i o n  2.  P h o t o r e s i s t d e p o s i t i o n , S h i p l e y AZ1350J, ( F i g . 3.3h),  3.  A p r e b a k i n g a t 70°C f o r 30 m i n u t e s ,  4.  Ohmic c o n t a c t mask alignment and exposure ( F i g . 3 . 3 i ) ,  5.  A s o a k i n g i n 26.0°C chlorobenzene f o r 2 minutes f o l l o w e d by p h o t o r e s i s t development. (Fig.  (The chlorobenzene i n c r e a s e s the s t r e n g t h of the top l a y e r  3.3j) t o the d e v e l o p e r so t h a t an undercut edge p r o f i l e ( F i g . 3.3k)  r e s u l t s upon p h o t o r e s i s t 6.  3.2.1),  development.)  Thermal e v a p o r a t i o n of AuGe (88% Au, 12% Ge) t o t h i c k n e s s of 300 nm u s i n g VEECO VE400 ( F i g . 3.31).  7.  Removal of unnecessary m e t a l by immersion i n a c e t o n e , l i f t o f f , ( F i g . 3.3m). The ohmic c o n t a c t s were then a l l o y e d f o r 1 minute i n a M i n i B r u t e  f u r n a c e p r e h e a t e d to 450°C ( t o c r e a t e an n In  +  r e g i o n beneath the c o n t a c t s ) .  the f i n a l p r o c e s s s t e p , gate m e t a l l i z a t i o n , the l i f t o f f  was used w i t h the gate m e t a l mask.  procedure  I n t h i s p r o c e s s A l was deposted t o 0.5  t h i c k n e s s by t h e r m a l e v a p o r a t i o n u s i n g a VEECO VE400 ( F i g . 3.3n).  um  SI  GaAs  ( Q ) Wafer p r e c l e a n  ////////  SiO? SI  (b)  GaAs  Implant mask d e p o s i t i o n  A\resist\\w\w ///SiO?//////////////  \\\  ///V  SI  (C)  //////////////  GaAs  E t c h o f r e g i s t r a t i o n marks  resist  \ \ \ W ////, w / / /  LlAl  SI  S1O2// GaAs  ( ( j ) Opening o f windows f o r i m p l a n t  F i g . 3.3  F a b r i c a t i o n sequence f o r t h e t e s t d e v i c e a r r a y  18  1 iI  //SiO?////  • N_ implant SI (e)  j  GaAs  Implantation  ///////////Si02 ////////////////// i N implant SI (f)  GaAs  E n c a p s u l a t i o n and a n n e a l i n g  |_N_ implant SI  (g)  —r I -1  GaAs  Wafer c l e a n  \ \ \ \ \ \ \ \ \  Li^J  r e s i ! S T \ \ \ \ \ \ \ \ \ \ \ -\ x  j N implant S I GaAs  (h )  '  Photoresist deposition  F i g . 3.3  cont'd.  j  exposed area V N X \ \\ \l  k\\\\l  I n implant S I GaAs ( 1 ) Photoresist  N\resisi \ \ !  exposure  modified layer \ \ w w \ J \\\ [_N implant SI  L\ rpqist \ \  1 t  GaAs  Chlorobenzene soak  f\W\[ |\\ 1  :_ N jrnpbnt SI  'pesist.A «  GaAs  (k) P h o t o r e s i s t development  |\\\|  j_ N jmpj.qnt _ _ J SI  GaAs  ( L) Source-drain m e t a l l i z a t i o n  • F i g . 3.3  cont'd.  N jmpLant SI (iTl)  J  GaAs  Removal o f p h o t o r e s i s t  gate N implant S 1 GaAs (n)  Gate m e t a l l i z a t i o n  F i g . 3.3  cont'd.  r i  21  4.  4.1  MEASUREMENTS ON THE  TEST DEVICE ARRAY  A c t i v e Layer E v a l u a t i o n To assess  S e c t i o n s 3.2.2  the d i r e c t i m p l a n t a t i o n and a n n e a l i n g process  and  were examined:  3.2.3  described i n  the f o l l o w i n g p r o p e r t i e s of the i m p l a n t e d  regions  sheet r e s i s t a n c e , H a l l m o b i l i t y , a c t i v a t i o n , c a r r i e r d e n s i t y  p r o f i l e , and d r i f t m o b i l i t y p r o f i l e . Sheet r e s i s t a n c e , H a l l m o b i l i t y , and a c t i v a t i o n measurements were made u s i n g the van der Pauw c r o s s ( s t r u c t u r e #3,  F i g . 3.1).  Samples were p l a c e d  i n a magnetic f i e l d B (0.2T) d i r e c t e d normal to the c r o s s ( F i g . A l p h a S c i e n t i f i c 7500-W magnet and power s u p p l y were used. (200  uA) was  4.1a).  An  A current I  e s t a b l i s h e d between o p p o s i t e t e r m i n a l s of the c r o s s ( i . e .  between t e r m i n a l s B and D, F i g . 4.1b)  u s i n g a HP 6186B c u r r e n t source and  H a l l v o l t a g e V^ a c r o s s the o t h e r t e r m i n a l s ( i . e . between t e r m i n a l s A and measured ( w i t h a F l u k e 8050 v o l t m e t e r ) . calculated  Average H a l l m o b i l i t y UJJ was  the C)  then  using  A. R BI  (4.1)  s  where R  g  i s the a c t i v e l a y e r sheet r e s i s t a n c e (van der Pauw, 1958).  determine R  g  a c u r r e n t I ' (0-1 mA)  was  e s t a b l i s h e d across adjacent  (A and D) ( w i t h no a p p l i e d magnetic f i e l d ) and the v o l t a g e V o t h e r t e r m i n a l s (B and C) measured.  R  was s  (van der Pauw,  1958)  To terminals  across  then c a l c u l a t e d u s i n g  the  CURRENT SOURCE  POWER SUPPLY  D  holder  sample  (a)  (b)  MAGNET  B  F i g . 4.1 E x p e r i m e n t a l arrangement used f o r v a n d e r Pauw measurements (a) A p p a r a t u s (b) v a n d e r Pauw c r o s s  23  IT fti2  R  Activation,  n,  was  XL  (4.2)  I'  estimated u s i n g  measured sheet electron concentration  1  n =  ,  = implanted  where q i s the elementary  charge  dose  (4 Dq  u^R  g  and D the implanted  C a r r i e r d e n s i t y p r o f i l e s were determined  dose.  by the c a p a c i t a n c e - v o l t a g e  technique i n which the c a p a c i t a n c e of a Schottky diode 3.1)  was  measured as a f u n c t i o n of r e v e r s e b i a s , V, and  then g i v e n by ( e . g . Sze,  the p r o f i l e ,  N(x),  1981)  N ( X  )  = _JL_ A ? q eA''  [ M ^ f dv  where e i s the p e r m i t t i v i t y of GaAs (~ 1.16 and x the depth below the s u r f a c e (x = 1 MHz  ( s t r u c t u r e #1, F i g .  c a p a c i t a n c e meter (Boonton 71A)  1  x 10"  eA/C). was  (4.4  J  1 0  F/m),  C which was  A the diode  area  measured w i t h a  recorded under PDP8e computer  con-  t r o l u s i n g the system of Boyd (1980) and program MESCV w r i t t e n by J i L i j i u . The  arrangement used  to perform  the p r o f i l i n g s i s shown i n F i g .  D r i f t m o b i l i t y p r o f i l e s were measured w i t h the f a t FET's #8,  F i g . 3.1)  u s i n g the method of P u c e l and Krumm (1976).  biased i n i t s l i n e a r region ( V  D g  = 50 mV)  4.2. (structure  A f a t FET  and the modulation  was  i ^ i n i t s drain  c u r r e n t r e s u l t i n g from the a p p l i c a t i o n of a ' s m a l l - s i g n a l gate-source  voltage  24  SAMPLE HOLDER  CAPMETER bias  Out  A-D-C LXJ O  X  D-V-M  DC  LU  D-A-COFFSET VOLTAGE SUPPLY PDP 8/  e  COMPUTER  F i g . 4.2 E x p e r i m e n t a l arrangement used f o r C-V measurements  25  v  (20 m V gS  D M C  ) r e c o r d e d as a f u n c t i o n of the DC g a t e - s o u r c e b i a s V „ . D r i f t c  KJMo  mobilities  (JO  P ( x ) were then c a l c u l a t e d u s i n g R  *n  ( x )  = C V ^ DS gs  ( 4  '  5 )  where L i s the gate l e n g t h and C the gate c a p a c i t a n c e (determined by C-V measurements).  v ^ was d e r i v e d from a s i n e wave g e n e r a t o r (IEC F63) w h i l e a g  l o c k - i n a m p l i f i e r (PAR 5204) was used t o p r o v i d e an output p r o p o r t i o n a l t o i,/v Q  .  The apparatus used t o implement the p r o f i l i n g s i s shown i n F i g . 4.3.  gS  Sheet r e s i s t a n c e v a l u e s are t a b u l a t e d i n F i g . 4.4. A t y p i c a l C-V p l o t i s shown i n F i g . 4.5 and c a r r i e r d e n s i t y and d r i f t m o b i l i t y p r o f i l e i n F i g . 4.6.  Table 4.1 summarizes the a c t i v e l a y e r parameters.  From the r e s u l t s t h e  f o l l o w i n g comments can be made: 1.  D r i f t m o b i l i t y i s seen t o i n c r e a s e towards the s u b s t r a t e .  This behaviour  has been shown by Immorlica e t a l . (1981) t o c o r r e l a t e w i t h good RF p e r formance i n t h e i r i o n i m p l a n t e d GaAs power MESFET's w h i l e d e v i c e s which d i s p l a y e d a d e c r e a s i n g d r i f t m o b i l i t y p r o f i l e were found t o e x h i b i t slow p u l s e response of d r a i n c u r r e n t t o a p p l i e d gate v o l t a g e and premature s a t u r a t i o n of output power. 2.  L i u e t a l . (1980) have c a l c u l a t e d the t h e o r e t i c a l i m p l a n t range Rp and s t r a g g l e ARp f o r 100 KeV S i i m p l a n t a t i o n i n t o GaAs t o be 86 nm and 38 nm r e s p e c t i v e l y , so t h a t i t appears t h a t broadening has o c c u r r e d d u r i n g annealing.  +  SIGNAL GENERATOR!  VOLTAGE SUPPLY  VOLTAGE SUPPLY -  ,1M 1  <  10 1K  0-1P*  -A/VV-  sample L_  _  J in  10  LOCK-IN AMPLIFIER  ref  1  output  4.3  E x p e r i m e n t a l arrangement used f o r d r i f t m o b i l i t y  profiling KJ3  27  2.0 3.1  Rl R2  . 1.8  1.8 1.5  (b),(e),(d)  (a)  R3  1.3  1.5  1.5 1.6  R4  2.2  1.4  1.3 1.3  R5  4.0  1.5  1.4  1.3 1.3  R6  1.9  1.6  1.3  1.3 2.6  R7  >  1.4  1.5  3.2 0.6  C2  C3  C4  1.7  3.5 3.1  9.4  4.8  1.1  0.4  9.0 1.2  1.3  2.9  4.4 5.5  4.4  >  0.5  1.5  1.2  1.2 0.8  1.2  2.2  2.4 2.6  2.6  4.0  3.6  Cl  C2  C3  C4  C6  C7  C8  CIO  Cll  C12  2.6 3.1  4.1  5.8  0.7  >  2.0  2.8 2.6  Cl  R3 R2  (b)  Rl  R3  (d)  C5  >  2.9  1.2  1.4 1.4  1.5  1.6  5.6  0.6  1.1  1.0 1.3  1.2  1.2  Cl  C2  C3  C4  C6  C7  R3  4.2  3.2  2.8 2.1  R2  0.8  0.8  0.9  1.9  1.8  Rl  0.8  0.8  0.8 0.7  0.8  0.8  1.7  C2  C3  C4  C6  C7  C8  R2  (c)  C5  Rl  C5  1.4.  C5  >  C9  >  2.9 C8  C9  2.2  CIO C l l  F i g . 4.4 A c t i v e l a y e r sheet r e s i s t a n c e v a l u e s f o r w a f e r s e c t i o n s f a b r i c a t e d ( i n kx/a , ? =R *10 W o ) (a) Wafer 94-S13 (b) Wafer 43-S10 ( c ) Wafer 123-S131 (d) Wafer 51-T132 S  50  AO  LLI  o z  I °  30  20-  -A  F i g . 4.5  -3  -2 -1 GATE VOLTAGE[V]  C-V p l o t f o r sample 123-S131  (R1-C5)  I  50  1  100  — i  150  1  200  *~  250  DEPTH ( nm) F i g . 4.6 C a r r i e r d e n s i t y and d r i f t m o b i l i t y f o r sample 123-S131 (R1-C5)  profile  30  Table 4.1 - A c t i v e L a y e r P r o p e r t i e s  Sample  43-S10 (R2-C6)  Sheet R e s i s t a n c e , R ' s  [koy ]  Hall Mobility,  [cm /Vs]  ^  2  Percent A c t i v a t i o n , Peak Doping, N  n  4.  - 2  The average R 123-S131.  p  3.3x10  51-T132 (R1-C3)  1.3 3.3x10  3  1.5x10  0.8 3.6x10  3  74  50 1 7  1.6xl0  3  1 7  1.9x10  [nm]  102  100  107  [nm]  69  54  69  1 7  o b t a i n e d can be compared t o those of I m m o r l i c a e t a l . (1980)  for 3x10 cm 1 2  AR  1.3  49 3  Implant S t a g g l e ,  Activations  [%] [cm" ]  Q  Implant Range, R^  3.  D  123-S131 (R1-C5)  g  S i i m p l a n t s who r e p o r t  n's from 67-74%.  f o r wafer 51-T132 i s lower than of wafers 43-S10 and  (The f i r s t number i n the wafer d e s i g n a t i o n s p e c i f i e s the i n g o t  from which the wafer was c u t w h i l e the second number s p e c i f i e s the wafer p o s i t i o n w i t h r e s p e c t t o e i t h e r the seed S or t a i l T of the i n g o t ) . r e s u l t may r e f l e c t the f a c t t h a t i n g o t 51 was found by Cominco t o be t h e r m a l l y u n s t a b l e showing a r e s i s t i v i t y drop from 1 . 8 x 1 0 l . l x l O * tan f o l l o w i n g a 30 minute 850°C a n n e a l . 1  8  tan t o  This  31  4.2  Gate M e t a l l i z a t i o n E v a l u a t i o n To assess  the gate m e t a l l i z a t i o n p r o c e s s d e s c r i b e d  the f o l l o w i n g p r o p e r t i e s were examinated:  i n Section  current-voltage  3.2.4  characteristics,  b a r r i e r h e i g h t , i d e a l i t y f a c t o r , (gate m e t a l ) sheet r e s i s t a n c e , l i t h o g r a p h i c definition. Schottky  d i o d e c u r r e n t - v o l t a g e c h a r a c t e r i s t i c s were measured on a  T e k t r o n i x 577 curve t r a c e r . then d e r i v e d from the forward  Barrier  heights  c h a r a c t e r i s t i c s s i n c e f o r V>3kT/q  Schottky  d i o d e c u r r e n t d e n s i t y J i s approximated by:  (4.6)  where A* i s an e f f e c t i v e R i c h a r d s o n constant  (A*=8.7 A c m  - 2  K  - 2  f o r n type  GaAs, C r o w e l l e t a l . , 1965) T the diode t e m p e r a t u r e , and k Boltzmann's cons t a n t so t h a t  (4.7)  and  dV n = 2.30 kT * d ( l o g J )  where J  i s an e x t r a p o l a t e d c u r r e n t d e n s i t y a t zero b i a s ( F i g . 4.7).  (4.8)  Gate  32  F i g . 4.7 Schottky 123-S131 (R1-C5).  d i o d e c u r r e n t - v o l t a g e p l o t f o r sample  33  metal  sheet r e s i s t a n c e s Rg^ were estimated by measuring the r e s i s t a n c e  between the t e r m i n a l s of the gate metal s t r u c t u r e ( s t r u c t u r e #6, (by a c u r r e n t v o l t a g e t e c h n i q u e ) . m e t a l l i z a t i o n was Table 4.2 resistance.  checked  An SEM  u s i n g a scanning e l e c t r o n microscope  photograph of a 3 p The  3.  (SEM). sheet  F i g . 3.1)  to 1.33  be a r e s u l t of improper  is  (1982) has found  depending on s u r f a c e  that i d e a l i t y  cleaning factors  treatment.  B a r r i e r h e i g h t s o b t a i n e d are c o n s i s t e n t w i t h the commonly accepted f o r metals  gate  f o l l o w i n g comments can be made:  p r i o r to m e t a l l i z a t i o n as Miers  2.  MESFET ( s t r u c t u r e #11,  The h i g h i d e a l i t y f a c t o r s o b t a i n e d may  v a r i e d from 1.08  3.1)  P h o t o l i t h o g r a p h i c d e f i n i t i o n of the  l i s t s v a l u e s of b a r r i e r h e i g h t , i d e a l i t y f a c t o r and  shown i n F i g . 4.9. 1.  Fig.  on n-type GaAs (see, f o r example, Sze,  1981).  The gate l e n g t h of the 3 un MESFET i s c l o s e to 4 ym and d e f i n i t i o n i s poor i n d i c a t i n g  values  the  gate  the need f o r an improved mask alignment  technique.  Table 4.2  - Metallization Properties  Sample  Schottky B a r r i e r Height,  ^  [eV]  Schottky B a r r i e r I d e a l i t y F a c t o r , n Gate M e t a l Sheet  Resistance, R  Ohmic Contact R e s i s t a n c e , R  [Q/D]  [mjjcm ] 2  c  43-S10 (R2-C6)  123-S131 (R1-C5)  51-T132 (R1-C3)  0.74  0.73  0.73  1.3  1.4  1.3  0.2  0.2  0.2  0.27  0.32  0.22  10 pm  F i g . 4.8 SEM photograph (2000X mag.) MESFET sample 123-S131 (R2-C5)  f o r 3um  35  4.3  Ohmic Contact M e t a l l i z a t i o n E v a l u a t i o n To assess the ohmic c o n t a c t m e t a l l i z a t i o n p r o c e s s d e s c r i b e d i n S e c t i o n  3.2.4 measurements were made of s p e c i f i c ohmic c o n t a c t r e s i s t a n c e by the method of Berger  (1972).  The r e s i s t a n c e r „  between a d j a c e n t ohmic c o n t a c t  pads i and j ( s t r u c t u r e #5, F i g . 3.1) was measured and r e s i s t a n c e of a pad) determined  by a l i n e a r r e g r e s s i o n of  R r . . = 2R + — ij c w  where £  (the contact  . i j  (4.9)  I  i s the s e p a r a t i o n between pads i and j and w i s the w i d t h of the  pads. Values o b t a i n e d f o r s p e c i f i c c o n t a c t r e s i s t a n c e a r e l i s t e d i n Table 4.2.  S i n c e f o r microwave FET's s p e c i f i c c o n t a c t r e s i s t a n c e s of 1 0  - 5  tan  2  or  l e s s a r e d e s i r a b l e (Gupta e t a l . 1983) ohmic c o n t a c t s of lower r e s i s t a n c e a r e required.  Use of the h i g h dose n  +  i m p l a n t under source and d r a i n r e g i o n s  ( i . e . mask C F i g . 3.2) s h o u l d r e c t i f y the s i t u a t i o n .  4.4  MESFET E v a l u a t i o n To t e s t the o p e r a t i o n of the d e v i c e s produced i n the f a b r i c a t i o n s ,  c h a r a c t e r i s t i c s of the narrow gate MESFET's ( s t r u c t u r e #9-12, 14-16, F i g . 3.1) were checked on a T e k t r o n i x 577 curve t r a c e r . i t was found t h a t o p e r a t i o n a l 2-10  From these  measurements  um d e v i c e s can be produced but t h a t  improved p h o t o l i t h o g r a p h i c t o o l s a r e r e q u i r e d t o produce the 1 um d e v i c e s ( T a b l e 4.3).  (A d e v i c e was deemed o p e r a t i o n a l i f i t showed !_„ s a t u r a t i o n  36  and  c o u l d be p i n c h e d - o f f to 100  c h a r a c t e r i s t i c and F i g . 4.10  pA).  a I„„ ~ V  Table 4.3  Wafer  94-S13  # Devices  F i g . 4.9 r Q  shows a t y p i c a l I g~V] n  characteristic.  - MESFET Y i e l d  43-S10  123-S131  51-T132  Total 95 .72  27  26  25  17  10 voi Gate 8 "  .70 .52  .50 .38  .84 .76  .88 .94  6 4  " ••  .48  .23  .62  " "  1  "  .50 .46 .35 0  .76 .71  3 2  .59 .59 .48 0  .80 .72 .76 .64 0  .76 .76 .12  .63 .54 .02  .48  .35  .65  .71  .53  TOTAL  Table 4.4  lists  .62 .54  the DC c h a r a c t e r i s t i c s of v a r i o u s 3 pm MESFET's.  The  AC behaviour of t h r e e of these d e v i c e s (123-S131 R1-C8, 51-T132 R1-C6, and 43-S10 R2-C5) were checked  over the frequency range  network a n a l y z e r ( a t M i c r o t e l P a c i f i c Research, have a c u t o f f frequency of about  3 GHz.  2-5  i n the d e v i c e s .  The  on a HP8409  Burnaby, B.C.)  a l . , 1975).  to  gate-source  t h e o r e t i c a l c u t o f f frequency f o r an  i n t r i n s i c 3 pa MESFET having no p a r a s i t i c components i s about et  and found  T h i s r e s u l t i s reasonable  c o n s i d e r i n g the h i g h ohmic c o n t a c t r e s i s t a n c e and l a r g e s e p a r a t i o n (~ 4 pm)  GHz  10 GHz  (Pucel  38  Fig."4.10  I  -V  characteristics  f o r 3 pm MESFET sample 123-S131 (R1-C5)  39  Table 4.4 - Device Parameters of 3 um MESFET's  43-S10  Sample  43-S10 123-S131 123-S131 51-T132 51-T132  (R2-C5) (R2-C6) (R1-C5)  ^"DSAT  @  V  DS  = 4 V  V  GS  @  ^S"  1 0 0  V  GS  @  ^S"  1 0  V  GS  @  ^S"  G  m  @  V  DS  = 4 V  1  * * *  (R1-C8)  (R1-C6) (R1-C3)  16  15  19  19  2.97  2.54  3.10  3.12  2.82  3.19  2.74  3.30  3.34  -  3.55  3.35  2.91  3.44  3.48  5  6  5  6  8  8  [mA]  13  [-v]  2.74  [-v]  3.14  [-v] [mA/V]  13  -  To check MESFET d r a i n c u r r e n t s t a b i l i t y 3 ym d e v i c e 123-S131 (R1-C5) was b i a s e d a t Vpg=lV and a gate v o l t a g e a p p l i e d o f s u f f i c i e n t magnitude (V_ «-3V) t o reduce I _ t o 100 uA. C  voltage was ;  I  . f o l l o w i n g the a p p l i c a t i o n of the g a t e  then monitored on a c h a r t r e c o r d e r .  I  was found t o be s t a b l e  t o w i t h i n ±5% of 100 pA over a p e r i o d of 30 minutes a r e s u l t t h a t d i f f e r s from those I t o h and Y a n a i (1980) and I t o h et a l . (1981) who r e p o r t e d  drain  c u r r e n t d r i f t s o f 20-40% ( a t t r i b u t e d t o Cr t r a p p i n g l e v e l s ) f o r MESFET's formed by e p i t a x y on Bridgman s u b s t r a t e s .  40  5.  5.1  DEEP LEVEL TRANSIENT SPECTROSCOPY  Basic Principles S i n c e i t s i n t r o d u c t i o n by Lang ( 1 9 7 4 ) , deep l e v e l t r a n s i e n t s p e c t r o -  scopy (DLTS) has proven a v e r y u s e f u l t e c h n i q u e f o r i n v e s t i g a t i n g deep l e v e l s i n semiconductor d e v i c e s .  I t enables a n o n - d e s t r u c t i v e e v a l u a t i o n of the  energy l e v e l E^, and e l e c t r o n ( h o l e ) c a p t u r e c r o s s s e c t i o n o" ( o^) of the major n  deep s t a t e s i n a sample.  Deep l e v e l c o n c e n t r a t i o n s may a l s o be d e t e r m i n e d .  DLTS i s based on the m o d u l a t i o n and measurement of the d e p l e t i o n r e g i o n c a p a c i t a n c e C ( t ) of a pn j u n c t i o n or S c h o t t k y d i o d e .  To a n a l y z e , f o r  example, a p n diode f o r m a j o r i t y c a r r i e r t r a p s i n the n r e g i o n ,  sample  +  temperature T i s v a r i e d and a v o l t a g e V ( t ) a p p l i e d ( F i g . 5.1). tg-t^  t r a p s i n the u n d e p l e t e d n r e g i o n are f i l l e d w i t h e l e c t r o n s .  b i a s i s changed from V W  3  During period  1  to V  2  the d e p l e t i o n r e g i o n w i d t h expands from Wj^ t o  w h i l e the c a p a c i t a n c e drops from  t o Cy  Traps at a depth between  and Wj^ which were f i l l e d are now emptied at a r a t e dependent energy l e v e l and e l e c t r o n c a p t u r e c r o s s s e c t i o n .  3  The r e l e a s e of t r a p p e d t o the steady  g  2  W  on the t r a p ' s  c a r r i e r s r e s u l t s i n a r e l a x a t i o n of the d e p l e t i o n w i d t h from W state value W  When the  and hence a r e l a x a t i o n of the c a p a c i t a n c e from C  3  to  C. 2  The t r a n s i e n t s i g n a l S ( t ) i s p r o c e s s e d w i t h a d u a l channel boxcar averager.  The c h o i c e of boxcar s a m p l i n g times t ^ and t  r a t e window RC of the system (Eq. 5.12).  2  f i x e s the so c a l l e d  When the decay c o n s t a n t T of S ( t )  i s e q u a l t o the r a t e window, the output of the boxcar r e g i s t e r s a maximum. As the sample temperature i s scanned, a DLTS spectrum of S ( t ) - S ( t ) v e r s u s T 1  i s o b t a i n e d ( F i g . 5.2).  2  I f more than one type of deep l e v e l i s p r e s e n t i n  DLTS T R A N S I E N T  W,  v(t)H  +  •hi-  n  +  (a)  v'(t)-  p*  n  +  v(t)H  ir  (b)  F i g . 5.1 B a s i c p r i n c i p l e o f DLTS g e n e r a t i o n (c) Trap emptying  (a) Steady s t a t e  (b) Trap  filling  S(T)  42  F i g . 5.2 B a s i c p r i n c i p l e o f d u a l channel b o x c a r s a m p l i n g o f DLTS t r a n s i e n t  43  the sample, s e v e r a l peaks w i l l appear i n the spectrum.  By s e l e c t i n g v a r i o u s  r a t e windows and r e p e a t i n g the temperature scan a f a m i l y o f DLTS s p e c t r a a r e o b t a i n e d from which t r a p d a t a may be c a l c u l a t e d (as d e s c r i b e d i n S e c t i o n 5.2).  5.2  Channel Conductance DLTS Channel conductance  DLTS (CDLTS) i s a u s e f u l t e c h n i q u e t o a s s e s s t h e  deep l e v e l s i n t h e channel of a MESFET ( A l d e r s t e i n , 1976). source v o l t a g e ( V  n  «50 mV) i s a p p l i e d .  V  Do  A small drain to  i s s e t t o zero t o a l l o w e l e c t r o n CJO  t r a p s i n the channel t o be f i l l e d .  V_  c  i s then stepped t o V  (JO  0  (J  (V ,<V <0). a  1  o  The  (J  gate d e p l e t i o n r e g i o n widens and a t r a n s i e n t channel c u r r e n t develops due t o the r e l e a s e of e l e c t r o n s from the expanded d e p l e t i o n r e g i o n . An e x p r e s s i o n f o r the channel conductance  t r a n s i e n t may be d e r i v e d f o r  a MESFET of gate l e n g t h L, gate w i d t h Z, and z e r o gate v o l t a g e channel depth a.  I t i s assumed t h a t a u n i f o r m a c t i v e l a y e r s h a l l o w donor d e n s i t y N^ e x i s t s  and t h a t a s i n g l e e l e c t r o n t r a p o f d e n s i t y N^, i s p r e s e n t .  N e g l e c t i n g the  r e s i s t a n c e of the unmodulated channel r e g i o n s , the conductance  of the MESFET  G(t) i s  Zola-X ( t ) ] =4  G(t) =  (5.1)  where a i s the c o n d u c t i v i t y of the a c t i v e l a y e r and X ^ ( t ) i s the gate d e p l e t i o n r e g i o n depth measured from the zero gate b i a s v a l u e . gate b i a s i s stepped from 0 t o  I f a t time t=0 the  and the s t e a d y s t a t e conductance (J  f o r large  44  t isG  Q  ( w i t h a c o r r e s p o n d i n g d e p l e t i o n depth of X ^ ) , then the conductance  d i f f e r e n c e s i g n a l AG(t) (AG(t) = G - G ( t ) ) i s Q  Za[X,(t)-X, ] !^  AG(t)  (5.2)  Since X ^ ( t ) can be assumed t o be g i v e n by  2eV X  d  U  )  1/2  G  ^ q[N +N (l-exp-t/T)] *  =  D  *  ( 5  T  3 )  where i i s a time c o n s t a n t , one f i n d s t h a t  X  H  (  t  1  )  4 — = D  [  1/9  r  O  ? /  T  '  1  N ^  e  X  p  (  "  / t  /  ( 5  -  4 )  N T  )  Now i f N^,«Np Eq. (5.4) becomes  X (t) H f — A  N exp(-t/ ) T  "  1  +  J  2 N  L  do  Z B  (  5  '  5  D  so Eq. (5.2) can be w r i t t e n as  z  AG(t) =  °  x d  2 L N  ^ °  N  T 1  exp(-t/T)  (5.6)  )  45  which i s the d e s i r e d e x p r e s s i o n f o r the c h a n n e l conductance  transient.  A b l o c k diagram of the CDLTS system of t h i s t h e s i s i s shown i n F i g . 5.3.  The d r a i n v o l t a g e t o the FET i s d e r i v e d from a r e g u l a t e d power s u p p l y  w h i l e the p e r i o d i c gate b i a s i s s u p p l i e d by an IEC F33 p u l s e g e n e r a t o r .  A  s m a l l r e s i s t o r R (10 n) c o n v e r t s the channel c u r r e n t i n t o a v o l t a g e s i g n a l which i s s u b s e q u e n t l y a m p l i f i e d by a PAR 113 a m p l i f i e r .  The output from the  a m p l i f i e r goes t o the i n p u t of a PAR 162/165 d u a l channel boxcar  arrangement.  The boxcar output goes t o the Y channel of an HP 7044A X-Y p l o t t e r .  The X  channel of the p l o t t e r r e c o r d s the thermocouple v o l t a g e of the sample. The sample i s housed i n a l i g h t t i g h t chamber.  The chamber, w h i c h was  adapted f o r use from a p r e v i o u s s t u d y ( L e s t e r , 1982) i s i l l u s t r a t e d i n F i g . 5.4.  A f t e r the chamber i s evacuated t o a p r e s s u r e of l e s s than 10 t o r r ,  sample temperature i s lowered t o 100 K v i a l i q u i d n i t r o g e n c o o l i n g . t r a n s i s t o r i s used t o heat the sample.  A power  A c o p p e r - c o n s t a n t a n thermocouple,  s o l d e r e d t o the d e v i c e package, i s used t o m o n i t o r the t e m p e r a t u r e . The i n p u t s i g n a l t r a n s i e n t V . ( t ) t o the boxcar i s g i v e n by  (5.7)  V ( t ) = A RG(t)V. DS ±  A  where A^ i s the a m p l i f i e r g a i n and where i t i s as sumed t h a t R « [ G ( t ) ] . - 1  output of the boxcar V  The  (as a f u n c t i o n of temperature T) can then be e x p r e s s -  Q  ed as  V (T) = A [ V . ( ) Q  B  t l  (5.8)  out  VOLTAGE SUPPLY  PULSE GENERATOR  BOXCAR  trig out  chamber—T X-Y PLOTTER  sample I  I  thermocouple —  AMPLIFIER R=10  F i g . 5.3  B l o c k diagram o f channel conductance DLTS arrangement  n  Liquid N cryostick 2  I^ig. 5.4  Sample h o l d e r used f o r DLTS measurements  48  where A_ i s t h e v o l t a g e g a i n of the boxcar.  Then from Eq.'s (5.6) and (5.7)  Eq. (5.8) can be r e w r i t t e n as  A.A^RZ oV__N X 2LN T  V  The  T  "  )  temperature  temperature  [exp(-t /T) 2  dependence o f V  dependence of T.  Q  expC-t/x)]  (5.9)  i n Eq. (5.9) can be d e r i v e d from t h e  From t h e p r i n c i p l e of d e t a i l e d b a l a n c e t h e time  c o n s t a n t ( r e c i p r o c a l e m i s s i o n r a t e ) f o r an e l e c t r o n t r a p can be shown t o be  T = (o v n  n  N )-lexp[J^]  where o" i s the c a p t u r e c r o s s s e c t i o n , v n  E  c  (5.10)  c  t h e c o n d u c t i o n band energy, and N  £  n  t h e thermal v e l o c i t y o f e l e c t r o n s ,  the c o n d u c t i o n band d e n s i t y of s t a t e s .  A t r a p l e v e l of s i n g l e degeneracy i s assumed.  S i n c e v ^ and N  £  v a r y markedly  w i t h T, Eq. (5.10) i s more a p p r o p r i a t e l y e x p r e s s e d as  t=  ( o ^ ) " 2  1  where y i s e q u a l t o 2 . 2 8 x l 0 c m s K 2 0  1.7xl0 et a l . ,  2 1  cm  - 2  s  - 1  k  - 2  - 2  -1  exp(^2)  - 2  (5.11)  f o r e l e c t r o n t r a p s i n GaAs and t o  f o r h o l e t r a p s i n GaAs ( M a r t i n e t a l . , 1977, Mitonneau  1977). For a c e r t a i n v a l u e of x, c a l l e d  x , V m  Q  peaks.  By d i f f e r e n t i a t i n g Eq.  (5.9) w i t h r e s p e c t t o T and s e t t i n g t h e r e s u l t e q u a l t o zero one f i n d s t h a t  49  t V  t  r  On t  =  l  2  / t  (  which i s d e f i n e d as the r a t e window RC of t h e CDLTS s c a n . ture T  m  corresponding t o t h e peak i n V  ( F i g . 5.2) and t ^ and t  2  q  5  1  '  1  2  )  S i n c e the tempera-  i s o b t a i n e d from t h e DLTS spectrum  a r e known, one may w r i t e  F —E m  n  m  v  kl ' m  I f a second spectrum i s o b t a i n e d f o r a d i f f e r e n t r a t e window, a and E -E„ n c T r  are u n i q u e l y d e t e r m i n e d .  U s u a l l y s e v e r a l scans a r e made and a p l o t o f l o g T x 2  v e r s u s 1/T ( a c t i v a t i o n energy p l o t ) made.  E -E c  a  n  Trap parameters a r e then g i v e n by  = 2.30 km  T  a =(YlO )  d  b  (5.14)  _  1  ( 5  n  '  1 5 )  where m and b a r e the s l o p e and i n t e r c e p t , r e s p e c t i v e l y , of the best l i n e a r fit  t o the above p l o t . The c o n c e n t r a t i o n of a t r a p i s d e r i v e d from t h e h e i g h t V ( T ) of the Q  CDLTS peak.  From Eq. (5.9) N^, can be c a l c u l a t e d as  2LN_V (T ) n  A B  DS do  -t m  -t m  m  50  where x  m  i s g i v e n by ( 5 . 1 2 ) .  I f the a c t i v e r e g i o n of a MESFET i s formed by i o n i m p l a n t a t i o n t h e assumption o f a u n i f o r m l y doped channel r e g i o n i s v i o l a t e d . Eq.'s  (5.14) and (5.15) can s t i l l be expected  of E -E_, and a i n most c a s e s . c i n  Nevertheless,  to give a reasonable  estimate  Since the c o n d u c t i v i t y of an i m p l a n t e d  n e l can be taken t o be p r o p o r t i o n a l t o an average N  n  chan-  i t i s i n t e r e s t i n g to  note t h a t Eq. (5.16) r e v e a l s t h a t N^, may be c a l c u l a t e d s i m p l y from a knowl e d g e o f X^  5.3  Q  (which can be deduced from a c a p a c i t a n c e v o l t a g e measurement).  P h o t o c u r r e n t DLTS P h o t o c u r r e n t DLTS (PDLTS) i s a u s e f u l t e c h n i q u e t o assess the deep  l e v e l s i n a s e m i - i n s u l a t i n g sample (Fairman e t a l . , 1979, Hurtes e t a l . , 1978).  The d e v i c e s t r u c t u r e t h a t i s used i n PDLTS c o n s i s t s of two c l o s e l y  spaced ohmic c o n t a c t pads.  A b i a s V i s e s t a b l i s h e d between t h e pads and t h e  sample i s i l l u m i n a t e d w i t h bandgap l i g h t . w h i c h p o p u l a t e t r a p s i n the sample.  E l e c t r o n / h o l e p a i r s a r e generated  I f the sample i s i l l u m i n a t e d f o r a  s u f f i c i e n t l e n g t h o f time the c u r r e n t f l o w between the pads approaches a steady s t a t e value i .  I f the sample c o n t a i n s a t r a p of d e n s i t y N , the T  o c c u p a t i o n of the t r a p n,j, d u r i n g steady s t a t e i s g i v e n by s  n  T  = N s  T  [l +  e +a v p _ i . ) e +a v n p n n n  P  P  (5.17)  where e /e , a / a , v /v , and n/p a r e the e l e c t r o n / h o l e r a t e c o n s t a n t , n p n p n p c a p t u r e c r o s s s e c t i o n , thermal v e l o c i t y and c o n c e n t r a t i o n , r e s p e c t i v e l y  51  (Hurtes  et a l . , 1978). When the l i g h t i s removed ( a t t=0)  the c u r r e n t does not  immediately  f a l l t o i ^ ( t h e l e a k a g e f l o w ) but i n s t e a d g r a d u a l l y decays t o t h i s l e v e l t o the slow r e l e a s e of trapped  carriers.  The  decay c u r r e n t i p ( t ) I  s  due  given  by  i (t) = C{e n (t) + e [ N n  T  p  where n^, i s the d e n s i t y of o c c u p i e d c o n t a c t geometry ( M a r t i n and  T  - n (t)] }  t r a p s , C i s a constant  B o i s , 1978)  (5.18)  T  dependent on  and where i ^ h a s been n e g l e c t e d .  i t i s assumed t h a t i p ( t ) decays e x p o n e n t i a l l y w i t h time c o n s t a n t n^,(0) i s e q u a l to n^, Eq. s  MO v  that  (5.18) becomes  = Ce N [(l - r - ^ P ) " n n 1  n  x and  If  T  For an e l e c t r o n t r a p a »a and n p  f~ e 1=  »e n  (!+!») ^ e x p ^ ) . p  so  (5.19)  that  p  i (t) = C x - ^ e x p ^ ) .  A b l o c k diagram of the photoconductance DLTS (PDLTS) system of  (5.20)  this  t h e s i s i s shown i n F i g . 5.5.  The  CDLTS arrangement of F i g . 5.3  except t h a t a type ME7021IR l i g h t e m i t t i n g  d i o d e (900 nm,  l ' . O mW  @100  mA)  system u t i l i z e s the same apparatus as  mounted on the sample chamber i s used to  the  PULSE GENERATOR  syn  BOXCAR  trig out  chamber  n  ,p X-Y PLOTTER  sample  thermocouple  AMPLIFIER  Fdg. 5.5  B l o c k diagram o f p h o t o c u r r e n t DLTS arrangement N3  53  i l l u m i n a t e the sample through a window ( F i g . 5.4).  The  transient signal  i n p u t V_^(t) to the boxcar i s  V (t) = A R ±  A  i (t)  w h i l e the boxcar output V (T) d e r i v e d from Eq. o  -  t  (5.21)  (5.20) i s  l  2  - t  V (T) = A ^ R C x - ^ ^ x p ^ )-exp(—)]  (5.22)  q  where A., A  A„ and R are as d e f i n e d p r e v i o u s l y . B  w i t h respect to  T  ( I t o h and Y a n a i ,  and  I f V (T) i s d i f f e r e n t i a t e d o  the r e s u l t s e t e q u a l to zero  T  FFI  i s found t o s a t i s f y  1981)  (1 - ^ ) e x p £ i ) = m m  (1 - - ^ ) e x p h ^ ) . m m  (5.23)  Once T i s c a l c u l a t e d , a and E -E„, can be determined from Eq. (5.13) as i n m n c I CDLTS.  5.4  Measurements CDLTS measurements were made w i t h the system d e s c r i b e d i n S e c t i o n  t o o b t a i n i n f o r m a t i o n on the deep l e v e l s i n the channel r e g i o n of MESFET's f a b r i c a t e d i n Chapter 3.  the  3 pm MESFET's were examined over the  temperature range 100-350 K w i t h r a t e windows 1-100  ms.  5.2  54  CDLTS s p e c t r a f o r d e v i c e s 123-S131 (R1-C5), 43-S10 (R2-C6), and 51-T132 (R1-C3) a r e shown i n F i g . ' s 5.6-5.8.  Three e l e c t r o n t r a p s , l a b e l l e d  CE1, CE2, and CE3 a r e r e s o l v e d i n each sample.  The a c t i v a t i o n energy p l o t  ( o r DLTS " s i g n a t u r e " , M a r t i n e t a l . , 1977) of each t r a p i s shown i n F i g . 5.9. T a b l e 5.1 l i s t s d a t a on t r a p energy, c r o s s s e c t i o n , and c o n c e n t r a t i o n c a l c u l a t e d v i a Eq.'s 5.14-16.  Trap c o n c e n t r a t i o n s i n 51-T132 (R1-C3)  ( e s p e c i a l l y CE1) a r e lower than i n the o t h e r two d e v i c e s .  I n a d d i t i o n the I -  V c h a r a c t e r i s t i c s of 51-T132 (R1-C3) show l e s s h y s t e r e s i s than t h a t o f 123-S131 (R1-C5) ( o r 43-S10 R2-C6) (compare F i g . 4.9 w i t h F i g . suggesting  5.10)  t h a t one o r more of these t r a p s a r e r e s p o n s i b l e f o r h y s t e r e s i s .  Table 5.1 - Deep L e v e l s Detected  L a b e l A c t i v a t i o n Energy Log [eV]  by CDLTS  ( a [ c m ] ) x @ 300 K [us]  N  2  n  [10 cm ] 1 6  T  - 3  43-S10 123-S131 51-T132 (R2-C6) (R1-C5) (R1-C3) CE1  0.50  ±0.01  -12.8  77  2.5  2.5  0.5  CE2  0.27  ±0.02  -16.3  27  1.0  0.5  0.3  CE3  0.20  ±0.01  -17.2  13  0.5  0.4  0.3  To i n v e s t i g a t e s e m i - i n s u l a t i n g p r o p e r t i e s , s u b s t r a t e samples were prepared  so t h a t PDLTS measurements c o u l d be made.  c o n t a c t pads were d e f i n e d . w i d t h of each pad 250 ym.  On each sample AuGe ohmic  The s e p a r a t i o n of the pads was 50 um and the  55  CE1  150  200  250  TEMPERATURE [K] F i g . 5.6  A CDLTS spectrum f o r 3 p i MESFET sample 123-S131 (R1-C5)  CE1  Rate window = 25  ms  Gate v o l t a g e = 0 t o -2 pulse  CE3  CE2  V  57  L  ,  ,  200  250  ,  300  TEMPERATURE [K] P i g . 5.8  A CDLTS spectrum for 3 pm MESFET sample 51-T132 (R1-C3)  CE1  1000/T [K-'] F i g . 5.9  A c t i v a t i o n energy p l o t f o r t r a p s d e t e c t e d by CDLTS  59  60  PDLTS measurements were conducted u s i n g the system d e s c r i b e d i n S e c t i o n 5.3.  The temperature range i n v e s t i g a t e d was 100-330K.  were v a r i e d from 1 ms to 50 ms.  Rate windows  An i n t e r - p a d b i a s of 4 V and a l i g h t  inten-  s i t y s u f f i c i e n t t o g i v e a peak p h o t o c u r r e n t of 500 nA ( a t room temperature) were used. A PDLTS spectrum f o r sample 63-T42(A) i s shown i n F i g . 5.11. deep l e v e l s  labelled  PI t o P5 a r e r e s o l v e d .  Five  The PDLTS spectrum f o r sample  82-S14(A) shown i n F i g . 5.12 shows the same f i v e l e v e l s  but the r e l a t i v e  c o n c e n t r a t i o n (peak h e i g h t ) of the PI t o P2 l e v e l i n t h i s sample i s a p p a r e n t l y higher.  Of note i s the f a c t  t h a t i n g o t 82 ( l i k e 51) was found by Cominco  to be t h e r m a l l y u n s t a b l e upon 850°C a n n e a l ( T a b l e 5.2).  Trap s i g n a t u r e s a r e  shown i n F i g . 5.13 and t r a p d a t a l i s t e d i n Table 5.3.  Table 5.2 - P r o p e r t i e s of Cominco GaAs  Wafer Assessed By Cominco  R e s i s t i v i t y Before Anneal [ t a n ]  Resistivity After Anneal [ tan]  43-S10  43-S7  9.6 X 10 7  1.8 - 2.1 x 1 0  45-S93  45-S96  3.9 X 10  69-T42  63-T27  1.2 X 10 7  94-S13  94-S22  2.0 X 10  123-S131  123-S195  51-T132  51-T181  1.8 X i o  8  82-S14  82-S11  4.3 X 10  8  Wafer Obtained From Cominco  7  5  -  1 x 10  7  8 - 9 x 10 1.9 x 1 0  7  2.8 x 1 0  7  1.1 x 10  7  6  4  6.1 x 7.1 x 1 0  3  X10 P4 P3 P5  100  200 TEMPERATURE [ K l  P i g . 5.11  A PDLTS spectrum f o r sample 63-T42(A)  (Rate window = 10  TEMPERATURE [K] Fig.  5.12  A PDLTS spectrum f o r sample 82-S14(A)  (Rate window = 10 ms) N IOS3  1000/T [K-'l •Fig. 5.13  A c t i v a t i o n energy p l o t f o r t r a p s d e t e c t e d by PDLTS  64  Table 5.3 - Deep L e v e l s Detected  Label  A c t i v a t i o n Energy [eV]  PI  0.87  7.5 x 10-3  P2  0.50  7.3 x 1 0  P3  Log( a [ c m ] )  Log( a [ c m ] )  -8.6  -9.5  - 3  -13.8  -14.6  0.59  6.1 x 10-6  -10.3  -11.1  P4  0.38  5.3 x 1 0  - 6  -12.7  -13.5  P5  0.32  4.6 x 10-9  -12.6  -13.5  T  @ 300 K [s]  By PDLTS  2  n  2  p  PDLTS and CDLTS t r a p s i g n a t u r e s a r e compared i n F i g . 5.14 a l o n g  with  v a r i o u s l e v e l s from t h e r e v i e w of M a r t i n e t a l . (1977) and Mitonneau e t a l . (1977).  P o s s i b l e a s s o c i a t i o n s a r e P I w i t h EL12, P2 w i t h EL3, P3 w i t h EL4, P4  w i t h HL6 and P5 w i t h EL8. EL2, a v e r y commonly r e p o r t e d t r a p i n b u l k GaAs (Appendix A) was not d e t e c t e d i n t h i s work.  CE1, CE2, and CE3 c o u l d not be  i d e n t i f i e d w i t h any of the l e v e l s from the reviews  (which r e p o r t on t r a p s  d e t e c t e d by DLTS i n b u l k and/or e p i t a x i a l GaAs) or w i t h any of the PDLTS l e v e l s suggesting  t h a t the CDLTS l e v e l s a r e i n t r o d u c e d d u r i n g the i m p l a n t a -  t i o n annealing process.  (A s i m i l a r c o n c l u s i o n has been made by Rhee e t a l . ,  (1982) who d e t e c t e d a 0.52 eV e l e c t r o n t r a p i n S i i m p l a n t e d i n the s u b s t r a t e ) .  GaAs not d e t e c t e d  The complete l i s t of t r a p s o f M a r t i n and Mitonneau i s  g i v e n i n Appendix C along w i t h the r e s u l t s of subsequent DLTS s t u d i e s ed by t h i s  author.  review-  66  6.  6.1  HYSTERESIS-FREQUENCY SPECTROSCOPY  Theory A u s e f u l procedure to study the h y s t e r e s i s e f f e c t seen i n the  I-V  c h a r a c t e r i s t i c s of GaAs MESFET's i s to v a r y the v o l t a g e sweep f r e q u e n c y . sweep f r e q u e n c i e s f » x  (where T i s the time c o n s t a n t  - 1  of the t r a p s  For  causing  h y s t e r e s i s ) t r a p s cannot respond to the change i n v o l t a g e so c u r r e n t l o o p i n g can be expected to be n e g l i g i b l e . completely  For sweep f r e q u e n c i e s f « x  - 1  traps  f o l l o w the change i n v o l t a g e so c u r r e n t l o o p i n g can a g a i n  expected to be n e g l i g i b l e .  T h e r e f o r e , f o r a sweep frequency  f «T  can be  current  - 1  l o o p i n g s h o u l d be a maximum. H y s t e r e s i s i n MESFET d r a i n c u r r e n t v s . gate v o l t a g e (I^-Vg) c h a r a c t e r i s t i c s i s a n a l y z e d w i t h the f o l l o w i n g a p p r o x i m a t i o n s We  and  assume t h a t there i s o n l y one d o n o r - e l e c t r o n  a c t i v e r e g i o n of the t r a n s i s t o r .  assumptions.  t r a p p i n g l e v e l i n the  I t s c o n c e n t r a t i o n i s N^, where N <<N T  i s the s h a l l o w donor c o n c e n t r a t i o n of the n-type a c t i v e r e g i o n ) . and doping are taken to be u n i f o r m . i n c l u d e occupied s t a r t decaying  Q  (N  Q  Both t r a p s  When the d e p l e t i o n r e g i o n i s expanded t o  and, hence, n e u t r a l t r a p s , t h e i r c o n c e n t r a t i o n i s assumed to  e x p o n e n t i a l l y (as e l e c t r o n s l e a v e them).  As shown i n F i g . 6.1(a), a saw-tooth waveform i s used to sweep V^ l i n e a r l y from zero to -V J  t  m  m  , i . e . , V = -V t / t , where V i s the amplitude G m m m  i s the p e r i o d of the saw-tooth waveform.  and  V_ i s assumed t o r e t u r n t o zero o  so r a p i d l y t h a t the o c c u p a t i o n of the t r a p s i n the d e p l e t i o n r e g i o n i s f r o z e n during this  process.  (a)  V  FROM  6  0  TO  -V, m  (b)  O + O + • + + +• + + + + + O + • + • W  (0  Wr, V  FROM - V  G  m  TO  0  i  (d) W  +  m  IONIZED  DONOR  TRAP  N E U T R A L  DONOR  TRAP  S H A L L O W  DONOR  F i g . 6 . 1 I o n i z a t i o n o f traps i n the depletion region due t o t h e sweep o f gate v o l t a g e w i t h a saw-tooth waveform (a) Saw«tooth v. aveform (b) C o n c e n t r a t i o n o f i o n i z e d donors f o r V from 0 t o - V (c) I o n i z a t i o n i n S c h o t t k y gate d e p l e t i o n r e g i o n (d*f C o n c e n t r a t i o n o f i o n i z e d donors f o r from *-V ;to 0. T  68  The  d e p l e t i o n w i d t h at zero gate b i a s ,  voltage V^. than  , corresponds to the  built-in  For n e g a t i v e gate b i a s e s , the d e p l e t i o n w i d t h i s always g r e a t e r  and the t r a p s i n s i d e  can hence be c o n s i d e r e d  to be  completely  i o n i z e d , so t h a t  W.  1  -  •  b l  where e i s the p e r m i t t i v i t y of the semiconductor. from zero to V_,  As the gate v o l t a g e changes  the d e p l e t i o n w i d t h i n c r e a s e s to W ( F i g . 6.1b).  charge c o n c e n t r a t i o n N(x)  i n the r e g i o n  N(x)  =  N  The  < x < W can be expressed  D  + 6(x)  space  as  ,  (6.2)  where 6(x) i s the i o n i z e d t r a p c o n c e n t r a t i o n w i t h i n t h i s d e p l e t i o n r e g i o n . The  r e l a t i o n between the d e p l e t i o n w i d t h W and the gate v o l t a g e  can  be found by s o l v i n g  W / N(x) xdx W. x  Since  «  N^,  neglected.  V - / - dV o G  .  (6.3)  q  6(x) i n Eq.(6.2) w i l l be much s m a l l e r than Np.  i t e r a t i v e method can be used. region  =  At f i r s t , the i o n i z e d t r a p s i n the d e p l e t i o n  < x < W are i g n o r e d , i . e . , the second term of Eq. From Eq.  (6.3).  Hence an  (6.2) i s  69  2eV n  Eq.  (6.4) i s a f i r s t  V  D  N  m  V_  n  D  T  1  /  2  m  approximation to the r e l a t i o n between W and V . G  The moment t a t which p o s i t i o n W s t a r t s t o d e p l e t e  can be o b t a i n e d  from Eq. ( 6 . 4 ) C  (2 W " ~ ^  =  m  m  N ^ N l ) Sn D T  A b e t t e r approximation of N(x) at V be made. considered  600  Since the c o n c e n t r a t i o n t o be decaying  -  » (l-e p T  X  '  (  6  '  5  )  i n the r e g i o n W. < x < W can then  of the n e u t r a l t r a p s i n t h i s r e g i o n i s  exponentially,  (-  6(x) of Eq. (6.2) can be expressed as  ( ^ - - I S l J ^ - Jt.J/x)) m m D T qN  m  . (6.6)  D  The time when the gate v o l t a g e p o s i t i o n x depleted  changes t o V„ i s -V„t /V and the moment when G G m m  i s estimated  w i t h Eq. ( 6 . 5 ) .  by s u b s t i t u t i n g Eq. (6.6) i n t o Eq. ( 6 . 2 ) . Eq.  Hence, N(x) can be o b t a i n e d  T h i s new N(x) i s s u b s t i t u t e d i n t o  (6.3) the s o l u t i o n of which i s a c l o s e r approximation of the r e l a t i o n  between the d e p l e t i o n width W and the gate v o l t a g e  qN D q  V  bi  N D  N T  r  (  V t G m  n  r  r  m  t r  „  and can be w r i t t e n as  4 9  qN^ D  V, . bi D  ^  n  x  70  V  G  „  N  • ~ \T ti" m qN  1 / 2 D  T  ^ '  D  ) m  *  7 )  T  N V , a = ^ - j - ^ - and 3 = — D T m T  By s e t t i n g L = w(  ( 6  b ±  N ^ p r ^ - , Eq. (6.7) can be D T D  simplified to  L 2  3"  a ( e x p ( ! ^ m  )) ( e x ( - ^ ( L ^ ) ) - ! ) ^ - 2  P  L, which i s r e f e r r e d as the n o r m a l i z e d  - ^ (l-a) m m  depletion width  later,  .  (6.8)  can be  esti-  mated as a f u n c t i o n of V„/V and t / T by u s i n g Newton-Raphson i t e r a t i o n . ti m m When t h e g a t e v o l t a g e reaches ~ V , the d e p l e t i o n w i d t h i s d e f i n e d as m  W w h i c h can be o b t a i n e d by s u b s t i t u t i n g -V t o V ^ i n Eq. ( 6 . 7 ) . m  m  We now 6.1cf).  consider  t h e r e t u r n of the gate v o l t a g e from -V  t o zero ( F i g .  The r e l a t i o n b e t w e e n t h e d e p l e t i o n w i d t h W' and the gate v o l t a g e  c a n be o b t a i n e d s i m i l a r l y by s o l v i n g W' / N(x) xdx W  Since  the t r a p  =  V - / - dV 1 m  (6.9)  G  _\7  occupancy i s assumed t o be f r o z e n d u r i n g  this  can be o b t a i n e d by s u b s t i t u t i n g Eq. (6.6) t o Eq. (6.2) w i t h V s o l u t i o n of Eq. (6.9) i s  Q  process,  = -V » m  The  N(x)  71  L.2-I/2-  a  (exp(-^  ) ) ( e * p ( ^ ( L - g ) )-exp ( ^  ( ' 2 - ) ) ) i - - (l+ m  2  L  ^) m  B  (6.10) where qN  L  r ——  = w m  1 / 2 D  m  v  i  2 ev m  and qN  1"  D  m  L' can then be c a l c u l a t e d as a f u n c t i o n of V_/V and t / x. G m m The e x t e n t of h y s t e r e s i s observed i n the I - V characteristicsi s D G d e f i n e d as the d i f f e r e n c e ( A l p ) between the c u r r e n t 1^ (when the gate v o l t a g e changes from zero t o V„) G reaching  -  V ).  and  I ' (when the v o l t a g e r e t u r n s to t h i s V a f t e r D L»  W i t h the p r e c e d i n g  m  f o r m u l a t i o n , the h y s t e r e s i s can  be  i n t e r p r e t e d as a consequence of the i n e q u a l i t y of L and L' at the same gate v o l t a g e because s i n c e 1^ i s c o n s i d e r e d to be p r o p o r t i o n a l to the channel w i d t h , AI-. i s p r o p o r t i o n a l t o AL = L-L'. AL at V = V has been u CJ Z m c a l c u l a t e d as a f u n c t i o n of x/t  for d i f f e r e n t concentrations  of deep l e v e l  m traps ( F i g . vs.  x/t  m  6.2a).  Fig.  with different V  6.2b m  of the maximum of the c u r v e , the v a l u e s of N  1  m  shows f i v e more curves of AL ( a t V  values. AL v s .  g  = -  V) m  These r e s u l t s suggest t h a t the p o s i t i o n T  ^ > m  does not depend s i g n i f i c a n t l y  and V i n the i n d i c a t e d range. m  on  The maxima of these curves  which correspond to the maximum e x t e n t of h y s t e r e s i s at the i n d i c a t e d c o n d i t i o n s always o c c u r at x/t  =0.4. The o c c u r r e n c e of a maximum l o g i c a l l y m f o l l o w s the two q u a l i t a t i v e c o n s i d e r a t i o n s : (1) i f t « x the t r a p s i n the - 1  F i g . 6.2 The d i f f e r e n c e ( L ) between t h e n o r m a l i z e d d e p l e t i o n w i d t h when V changes from zero t o -W2 as a f u n c t i o n o f n o r m a l l i z e d sweep frequency (a) f o r d i f f e r e n t N (b) f o r d i f f e r e n t V T  ffi  73  d e p l e t i o n r e g i o n can c o m p l e t e l y  i o n i z e and  (2) i f t  - 1  respond t o the sweep i n v o l t a g e and remain n e u t r a l . hysteresis AIQ  the t r a p s cannot  I n both cases no  results. can be measured e x p e r i m e n t a l l y by sampling  c u r r e n t 1^ and frequency  »x  I ' at the same V~.  The  and  comparing the  r e s u l t a n t p l o t of Al,, v s . sweep  ( l / t ) w i l l be r e f e r r e d to as an I-V h y s t e r e s i s spectrum (IVHS) by m  analogy w i t h DLTS.  S i n c e Al  i s p r o p o r t i o n a l to AL, the frequency  the spectrum peaks g i v e s the time c o n s t a n t  x  *  0.4  of the t r a p s  t m  = (2.5f ) - l m  (6.11)  In a d d i t i o n , the energy l e v e l of the t r a p s can be e s t i m a t e d c o n s t a n t s at d i f f e r e n t temperatures and u s i n g Eq.  6.2  at which  by measuring time  (5.11).  Apparatus The  behaviour  system shown i n F i g . 6.3 of MESFET I^-V-  was  hysteresis.  assembled t o r e c o r d the Waveform g e n e r a t o r  generates a v o l t a g e ramp to c o n t r o l the frequency  frequency  1 (Servomex  LF51)  of the (saw-tooth) waveform  g e n e r a t e d by waveform g e n e r a t o r  2 (IEC F63)  X-Y  saw - t o o t h waveform i s i n p u t to the gate of  p l o t t e r (Moseley 135).  The  the MESFET sample and a comparator. connected to a DC sampled.  Two  n  and  supply used t o a d j u s t  o t h e r i n p u t of the comparator i s the  at which d r a i n c u r r e n t i s  p u l s e s are d e r i v e d from the output of the monostable  m u l t i v i b r a t o r s (MC Hence I  The  and a l s o d r i v e s the X - a x i s of a  74121) and used to t r i g g e r the two LF398 sample and  holds.  I ' are measured at a d e s i r e d V„ and i n p u t to a d i f f e r e n t i a l  F i g . 6.3  E x p e r i m e n t a l arrangement f o r h y s t e r e s i s measurements  75  amplifier.  The o u t p u t , a v o l t a g e p r o p o r t i o n a l t o A I ^ i s sent t o the Y - a x i s of  the p l o t t e r .  6.3  Measurements To t e s t the h y s t e r e s i s model and a p p a r a t u s , measurements were conducted  on 30 ym MESFET 45-S93 R4-C3 as t h i s d e v i c e (which was p r o c e s s e d by T e k t r o n i x Corp., B e a v e r t o n , Oregon) d i s p l a y e d prominent h y s t e r e s i s ( F i g . 6.4). IV, Vpg of 0.5V and sweep f r e q u e n c y range of 0-1 KHz were used.  A V  m  of  Sample  temperature was v a r i e d from 300-350 K ( u s i n g a Stratham SD6 oven). IVHS s p e c t r a a r e shown i n F i g . 6.5 r e v e a l i n g t h a t A l ^ does indeed peak at a c e r t a i n f r e q u e n c y .  The a c t i v a t i o n p l o t o b t a i n e d from the IVHS s p e c t r a  ( c a l c u l a t e d v i a Eq.'s 6.11, 5.11) i s shown i n F i g . 6.6.  A l s o shown i n F i g .  6.6 i s the a c t i v a t i o n p l o t f o r the sample determined by CDLTS measurements. I t i s e v i d e n t t h a t the IVHS and CDLTS d a t a agree ( i . e . both r e v e a l the presence of a 0.4 eV ( e l e c t r o n ) t r a p ) thus showing the u s e f u l n e s s of the IVHS method f o r s t u d y i n g h y s t e r e s i s i n GaAs MESFET's.  • F i g . 6.4  I - V Do  45-S93 (R4-C3).  characteristics  f o r MESFET  Do  Gate b i a s s t e p = -0.5 V  77  FREQUENCY (Hz) Fig.  6.5  H y s t e r e s i s s p e c t r a f o r MESFET  A5-S93  (R4-C3)  78  F i g . 6.6 A c t i v a t i o n energy p l o t f o r MESFET 45-S93 (R4-C3) as o b t a i n e d by h y s t e r e s i s and CDLTS measurements  79  7.  SUMMARY AND  CONCLUSION  ;  The purpose of t h i s t h e s i s was t o develop a GaAs MESFET p r o c e s s t e c h n o l o g y and t o o l s t o assess GaAs and i n t h i s r e s p e c t the f o l l o w i n g c o n t r i b u t i o n s have been made: 1.  A GaAs MESFET f a b r i c a t i o n process based on d i r e c t s e l e c t i v e i o n i m p l a n t a t i o n i n t o undoped LEC GaAs was developed which i s capable of p r o d u c i n g 2-10 un MESFET's o p e r a t i o n a l t o 3 GHz.  2.  A t e s t d e v i c e a r r a y was designed f o r use i n p r o c e s s , m a t e r i a l , and d e v i c e c h a r a c t e r i z a t i o n and t e c h n i q u e s f o r u s i n g the a r r a y demonstrated.  The  a r r a y s h o u l d be u s e f u l f o r f u t u r e process development at U.B.C. and once a s u i t a b l e p r o c e s s has been e s t a b l i s h e d f o r r o u t i n e s u b s t r a t e m o n i t o r i n g by Cominco. 3.  A channel conductance  DLTS system was c o n s t r u c t e d and i t s use i n  a s s e s s i n g a c t i v e l a y e r q u a l i t y shown. 4.  A p h o t o c u r r e n t DLTS system was c o n s t r u c t e d and i t s use i n m o n i t o r i n g substrate quality  5.  demonstrated.  A t e c h n i q u e f o r d e t e r m i n i n g the deep l e v e l s r e s p o n s i b l e f o r h y s t e r e s i s i n GaAs MESFET's was developed. S e v e r a l s u g g e s t i o n s f o r f u r t h e r work a r e made:  1.  A l t h o u g h the p r o c e s s developed was shown t o be capable of p r o d u c i n g o p e r a t i o n a l MESFET's improvements a r e r e q u i r e d b e f o r e GaAs MESFET IC's can be s u c c e s s f u l l y produced.  I n p a r t i c u l a r i t i s suggested t h a t f o r  f u t u r e GaAs MESFET f a b r i c a t i o n s t h a t n t h a t improved  +  s o u r c e - d r a i n i m p l a n t s be used,  p h o t o l i t h o g r a p h i c equipment be o b t a i n e d , and t h a t  80  gate-source  and d r a i n - s o u r c e s p a c i n g s be m i n i m i z e d .  the encapsulant  The use of S i g N ^ f o r  (now p o s s i b l e w i t h the r e c e n t a c q u i s i t i o n of a  Plasmatherm PK1250) may improve a c t i v a t i o n as E i s e n e t a l . (1982) c l a i m s that SigN^ i s superior to S i 0  2  i n p r e v e n t i n g Ga o u t d i f f u s i o n d u r i n g  annealing. 2.  F u r t h e r i n v e s t i g a t i o n s on the deep l e v e l s d e t e c t e d by CDLTS a r e r e q u i r e d . In p a r t i c u l a r s i n c e these l e v e l s appear t o be process induced  CDLTS  s p e c t r a s h o u l d be o b t a i n e d f o r r e g i o n s i m p l a n t e d w i t h d i f f e r e n t e n e r g i e s , s p e c i e s , and annealed w i t h d i f f e r e n t times and 3.  doses,  temperatures.  F i n a l l y , s i n c e the u s e f u l n e s s of the t e c h n i q u e s have been demonstrated, i t i s recommended t h a t the DLTS systems be automated t o a l l o w r o u t i n e m a t e r i a l a n a l y s i s and a c r o s s wafer scans t o be c o n v e n i e n t l y made.  81  REFERENCES 1.  A l d e r s t e i n , M.G. (1976), " E l e c t r i c a l Traps i n GaAs Microwave FET's," E l e c t r o n . L e t t . , 12, 297.  2.  Barna, A. and L i e c h t i , C.A. (1979), " O p t i m i z a t i o n of GaAs MESFET L o g i c Gates w i t h Subnanosecond P r o p a g a t i o n D e l a y s , " IEEE J . S o l i d - S t a t e C i r c u i t s , SC-14, 708.  3.  B e r g e r , H.H. (1972), "Contact R e s i s t a n c e and Contact R e s i s t i v i t y , " J . E l e c t r o c h e m . Soc.. 119. 507.  4.  Boyd, G.B. (1981), " S t u d i e s on G a l l i u m A r s e n i d e Technology," T h e s i s , UBC.  5.  C r o w e l l , C.R., Sarace, J.C. and Sze, S.M. (1965), "Tungsten-Semiconductor S c h o t t k y - B a r r i e r Diodes," Trans. M e t a l l u r i g c a l Soc. AIME, 233, 478.  6.  D a v i d , J.M and B u e h l e r , M.G. (1977), "A N u m e r i c a l A n a l y s i s of V a r i o u s Cross Sheet R e s i s t o r Test S t r u c t u r e s , " S o l i d S t a t e E l e c t r o n . jtO, 529.  7.  D r i v e r , M.C., Wong. S., P r z y b y s z , J.X., W r i c k , V.L., Wickstrom, R.A., Coleman, E.S. and Oakes, J.G. (1981), " M o n o l i t h i c Microwave A m p l i f i e r s Formed by I o n - I m p l a n t a t i o n i n t o LEC G a l l i u m A r s e n i d e S u b s t r a t e s , " IEEE Trans. E l e c t r o n D e v i c e s , ED-28, 191.  8.  Eden, R.C. ( 1 9 8 1 ) , "High-Speed GaAs I n t e g r a t e d C i r c u i t s , " p r e s e n t e d a t the High-Speed D i g i t a l T e c h n o l . Conf., San Diego, CA, J a n . 13-14, 1981, paper I I . 4 .  9.  E i s e n , F., K i r k p a t r i c k , C. and Asbeck, P. (1982), " I m p l a n t a t i o n i n t o GaAs," i n GaAs FET P r i n c i p l e s and Technology, J.V. D i l o r e n z o ed., A r t e c House, Washington, 117.  M.A.Sc.  10. Fairman, R.D., M o r i n , F . J . and O l i v e r , J.R. ( 1 9 7 9 ) , "The I n f l u e n c e o f S e m i - I n s u l a t i n g S u b s t r a t e s on t h e E l e c t r i c a l P r o p e r t i e s of H i g h - P a r i t y GaAs B u f f e r L a y e r s Grown by Vapour-Phase E p i t a x y , " G a l l i u m A r s e n i d e and R e l a t e d Compounds, I n s t . Phys. Conf. S e r . , 45, 134. 11. Fairman, R.D., Chen, R.T., O l i v e r , M.R. and Ch'en, D.R. (1981), "Growth of High P u r i t y S e m i - I n s u l a t i n g B u l k GaAs f o r I n t e g r a t e d - C i r c u i t A p p l i c a t i o n s , " IEEE Trans. E l e c t r o n D e v i c e s , ED-28, 135. 12. F u r u t s u k a , T., T s u j i , T., Katano, F., H i g a s h i s a k a , A. and Kurumado, K. ( 1 9 8 1 ) , " I o n Implanted E/D-Type GaAs IC Technology," E l e c t r o n . L e t t . , 17, 944. 13. Gupta, A., P e t e r s e n , W.C. and Decker, D.R. ( 1 9 8 3 ) , " Y i e l d C o n s i d e r a t i o n s f o r I o n Implanted GaAs MMIC's," IEEE Trans. E l e c t r o n . D e v i c e s , ED-30, 16.  82 14. Hasegawa, F., and M a j e r f e l d , A. (1975), " M a j o r i t y C a r r i e r Traps i n n-and p-type E p i t a x i a l GaAs," E l e c t r o n . L e t t . , L I , 286. 15. H a t z a k i s , M., C a n a v e l l o , B.J. and Show, J.M. Develop., J24_, 452.  ( 1 9 8 0 ) , IBM J . Res.  16. Holmes, D.E., Chen, R.T., E l l i o t , K.K., K i r k p a t r i c k , C.G. and Yu, P.W. ( 1 9 8 2 ) , "Compensation Mechanism i n L i q u i d E n c a p s u l a t e d C z o c h r o l s k i GaAs,: Importance of M e l t S t o i c h i o m e t r y , " IEEE Trans. E l e c t r o n D e v i c e s , ED-29, 1045. 17. Hooper, W.W. and L e h r e r , W.I. (1967), "An E p i t a x i a l GaAs F i e l d - E f f e c t T r a n s i s t o r , " P r o c . IEEE, _55, 1237. 18. H o r n b u c k l e , D.P., Van T u y l , R.L., " M o n o l i t h i c GaAs D i r e c t - C o u p l e d A m p l i f i e r s , " IEEE Trans. E l e c t r o n D e v i c e s , ED-28, 175. 19. Huber, A.M., L i n h , N.T., V a l l o d o n , M., Debron, J . L . , M a r t i n , G.M., Mitanneau, A. and M i r c e o , A. (1979), " D i r e c t Evidence f o r the Nonassignment of Oxygen of the Main E l e c t r o n Trap i n GaAs," J . A p p l . Phys., 50, 4022. 20. H u r t e s , C., B o u l o u , M., Mitonneou, A., and B o i s , D. (1978), "Deep L e v e l Spectroscopy i n High R e s i s t i v i t y M a t e r i a l s , " A p p l . Phys. L e t t . , 32_, 821. 21. I m m o r l i c a , A.A., Decker, D.R. and H i l l , W.A. ( 1 9 8 0 ) , "A D i a g n o s t i c P a t t e r n f o r GaAs FET M a t e r i a l Develoment and P r o c e s s M o n i t o r i n g , " IEEE Trans. E l e c t r o n D e v i c e s , ED-27, 2285. 22. Johnson, E . J . , K a f a l a s , J.A. and D a v i e s , R.W. ( 1 9 8 3 ) , "The Role of DeepL e v e l Centers and Compensation i n P r o d u c i n g S e m i - I n s u l a t i n g GaAs," J . A p p l . Phys., 54, 204. 23. K a t o , V., Dohsen, M., Kasahara, J . , T a i r o , K. and Watanabe, N. ( 1 9 8 1 ) , " P l a n a r N o r m a l l y - O f f GaAs JFET f o r High Speed L o g i c C i r c u i t s , " E l e c t r o n . L e t t . , L7, 951. 24. K i t a h a r a , K., N o k a i , K., S h i b a t u m i , A. and Ohkawa, S. ( 1 9 8 0 ) , " S u b s t r a t e B i a s E f f e c t on Ion-Implanted GaAs MESFET's," Jpn. J . A p p l . Phys., 19, L369. 25. L a g o w s k i , J . , Gatos, H.C., P a r s e y , J.M., Wada, K., K a m i n s k i , M. and W o l u k i e w i c z , W. (1982), " O r i g i n of the 0.82 eV E l e c t r o n Trap i n GaAs and i t s A n n i h i l a t i o n by S h a l l o w Donors," A p p l . Phys. L e t t . , 40, 342. 26. L i n g , D.V. ( 1 9 7 4 ) , "Deep L e v e l T r a n s i e n t S p e c t r o s c o p y : A New Method t o C h a r a c t e r i z e Traps i n Semiconductors," J . A p p l . Phys., 4^5, 3023. 27. Lang, D.V. and Logan, R.A. (1975), "A Study of Deep L e v e l s i n GaAs by C a p a c t i a n c e S p e c t r o s c o p y , " J . E l e c t r o n . Mat., _4, 1053.  83 28. Lang, D.V., Cho, A.Y., G r o s s a r d , A.C., Ilegems, M. and Wiegmann, W. ( 1 9 7 6 ) , "Study of E l e c t r o n Traps i n n-GaAs Grown by M o l e c u l a r Beam E p i t a x y , " J . A p p l . Phys., £ 7 , 2558. 29. Lehovec, K. and Z u l e e g , R. (1980), " A n a l y s i s of GaAs FET's f o r I n t e g r a t e d L o g i c , " IEEE Trans. E l e c t r o n D e v i c e s , ED-27, 1074. 30. L e s t e r , T.P. (1982), "A New Photon Counting Sensor O p e r a t i n g i n the Above-Breakdown Regime," Ph.D. T h e s i s , UBC. 31. L i u , S.G., Douglas, E.C., Wu, C P . , Magee, C.W., Narayan, S.Y., J o l l y , S.T., K o l o n d r a , F., and J a i n , S. ( 1 9 8 0 ) , "Ion I m p l a n t a t i o n of S u l f u r and S i l i c o n i n GaAs," RCA Review, 41, 227. 32. M a k i , D.W., E s f a n d i e r i a n d , R. and S i r a c u s a , M. Noise A m p l i f i e r s , " Microwave J . , _24, 103.  ( 1 9 8 1 ) , " M o n o l i t h i c Low  33. M a r t i n , G.M., Mitonneau, A., M i c e a , A. ( 1 9 7 7 ) , " E l e c t r o n Traps i n B u l k and E p i t a x i a l GaAs C r y s t a l s , " E l e c t r o n . L e t t . , JL3, 191. 34. M a r t i n , G.M. and B o i s , D. (1978), "An New Technique f o r the S p e c t r o s c o p y of Deep L e v e l s i n I n s u l a t i n g M a t e r i a l s A p p l i c a t i o n to the Study of SemiI n s u l a t i n g GaAs," i n Semiconductor C h a r a c t e r i z a t i o n Techniques, P.A. Barnes ed., E l e c t r o c h e m . Soc. P r o c , 78-3, 32. 35. M a r t i n , G.M., F o r g e s , J.P., Jacob, G. and H a l l a i s , J.P. ( 1 9 8 0 ) , "Compensation Mechansisms i n GaAs," J . A p p l . Phys., _5_1, 2840. 36. M a r t i n , G.M., J a c o b , G., P a i b l a u d , G., G a l t z e n e , A. and Schwab, C. ( 1 9 8 1 ) , " I d e n t i f i c a t i o n and A n a l y s i s of N e a r - I n f r a r e d A b s o r p t i o n Bands i n Undoped and Cr Doped S e m i - I n s u l a t i n g GaAs C r y s t a l s , " D e f e c t s and R a d i a t i o n E f f e c t s i n Semiconductors, I n s t . Phys. Conf. S e c , 59, 281. 37. Mead, C.A. ( 1 9 6 6 ) , " S c h o t t k y B a r r i e r Gate F i e l d - E f f e c t T r a n s i s t o r , " P r o c . IEEE, 54, 307. 38. Metz, E.P.A., M i l l e r , R.C. 2016.  and M o z e l s k y , R. ( 1 9 6 2 ) , J . A p p l . Phys.,  33,  39. M i e r s , T.H. (1982), " S c h o t t k y Contact F a b r i c a t i o n f o r GaAs MESFET's," J . E l e c t r o c h e m . S o c , 129, 1795. 40. Mitonneau, A., M a r t i n , G.M. and M i r c e a , A. ( 1 9 7 7 ) , "Hole Traps i n B u l k and E p i t a x i a l GaAs C r y s t a l s , " E l e c t r o n . L e t t . , 13, 366. 41. N o t t h o f f , J . and Z u l e e g , R. ( 1 9 7 5 ) , IEEE I n t . E l e c t r o n Devices Mtg. D i g . Tech. Papers 624. 42. P u c e l , R.A., Haus, H.A. and S t a t z , H. ( 1 9 7 5 ) , " S i g n a l and N o i s e P r o p e r t i e s of GaAs Microwave F i e l d E f f e c t T r a n s i s t o r s , " i n L. M a r t i n , Ed., Advances i n E l e c t r o n i c s and E l e c t r o n P h y s i c s , 38, Academic, New York, 195.  84 43. P u c e l , R.A. and Krumm, C.F. (1976), "Simple Method o f Measuring D r i f t M o b i l i t y P r o f i l e s i n T h i n Semiconductor F i l m s , " E l e c t r o n . L e t t . , 12, 240. 44. Rhee, J.K., B h a t t a c h a r y a , P.K. and Koyama, R.Y. (1982), "Deep L e v e l s i n S i - I m p l a n t e d and Thermally Annealed S e m i - I n s u l a t i n g GaAs:Cr," J . A p p l . Phys., 53, 3311. 45. Sze, S.M. (1981), P h y s i c s of Semiconductor  D e v i c e s , W i l e y , New York.  46. T s e r n g , H.Q., Macksey H.M. and N e l s o n , S.R. ( 1 9 8 1 ) , "Design, F a b r i c a t i o n , and C h a r a c t e r i z a t i o n o f M o n o l i t h i c Microwave Power FET A m p l i f i e r s , " IEEE T r a n s . E l e c t r o n D e v i c e s , ED-28, 183. 47. Udagawa, T., H i g a s h i u r a , M. and N o k o n i s i , T. (1980), " R e d i s t r i b u t i o n and V a p o r i z a t i o n of Cr I m p u r i t i e s i n S e m i - I n s u l a t i n g GaAs," i n SemiI n s u l a t i n g I I I - V M a t e r i a l s , Nottingham 1980, 108. 48. Van der Pauw, L . J . (1958), "A Method f o r Measuring S p e c i f i c R e s i s t i v i t y and H a l l E f f e c t of D i s c s of A r b i t r a r y Shape," P h i l . Res. Rep., _13, 1. 49. Van T u y l , R.L. and L i e c h t i , C.A. (1974), "High-Speed I n t e g r a t e d L o g i c w i t h GaAs MESFET's," IEEE J . S o l i d - S t a t e C i r c u i t s , SC-9, 269. 50. Welch, B.M., Shen, Y., Zucca, R., Eden, R.C. and Long, S . I . (1980), " L S I P r o c e s s i n g Technology f o r P l a n a r GaAs I n t e g r a t e d C i r c u i t s , " IEEE Trans. E l e c t r o n D e v i c e s , ED-27, 1116. 51. Wisseman, W.R., Macksey, H.M., Brehm, G.E. and S o u n i e r , P. (1983), "GaAs Microwave Devices and C i r c u i t s w i t h Submicron Electron-Beam D e f i n e d F e a t u r e s , " P r o c . IEEE, _71_> 667. 52. Yamasaki, K., Hamane, Y. and Kurumada, K. (1982), "Below 20 ps/Gate O p e r a t i o n w i t h GaAs S a i n t FETs a t Room Temperature," E l e c t r o n . L e t t . , 18, 592. 53. Yuba, Y., Gamo, K. and Nambo, S. (1982), "Deep L e v e l s i n Implanted and L a s e r Annealed GaAs S t u d i e d by C u r r e n t and C a p a c i t a n c e - T r a n s i e n t Measurements," GaAs and R e l a t e d Compounds, I n s t . Phys. conf. S e r . , 63, 221. 54. Z y l b e r s z t e j n , A., B e r t , G. and N u z i l l o t , G. (1979), "Hole Traps and t h e i r E f f e c t s i n GaAs MESFETs," G a l l i u m A r s e n i d e and R e l a t e d Compounds, I n s t . Phys. Conf. S e r . , 45, 315.  85  APPENDIX A - S u b s t r a t e Compensation  Considerations  The deep l e v e l b e l i e v e d to be r e s p o n s i b l e f o r compensating undoped LEC GaAs i s the so c a l l e d EL2 l e v e l ( M a r t i n et a l . , 1977).  T h i s l e v e l which i s  commonly d e t e c t e d i n GaAs i s a deep donor w i t h a t h e r m a l a c t i v a t i o n energy E^ of 0.75  eV below E  or more p r e c i s e l y ( M a r t i n et a l . , 1980)  c  E - E ( E L 2 ) = 0.759 - [2.37 x 1 0 V l ] T eV . -  c  T  I f EL2 does govern the compensation i n undoped LEC GaAs one may  write  from charge n e u t r a l i t y  p + N, a  where n, p, N, , " d +  J  r  N,"t and N dd a  -  +  + N + = n + N ~ ad a  a r e the d e n s i t i e s of e l e c t r o n s , h o l e s , i o n i z e d  s h a l l o w donors, i o n i z e d deep EL2 d o n o r s , and i o n i z e d s h a l l o w respectively.  (A.l)  acceptors,  To s o l v e t h i s e q u a t i o n f o r n at room temperature one  may  assume t h a t N « N , and N ~ «N .N/JT i s c a l c u l a t e d from d d a a dd +  J  dd 1 + exp[(E -E )/kT] N  N  dd  =  F  ( A , 2 )  T  where E„ i s the Fermi energy w h i l e n and p a r e governed by r  n = N  c  exp[-(E -E )/kT] c  F  (A.3)  0  86  p = N e x p [ - ( E -E )/kT] v r v  (A.4)  where N , N i s the e f f e c t i v e d e n s i t y of s t a t e s i n the c o n d u c t i o n , v a l e n c e c' v ' J  band.  (N =4.7x10 c m c 1 7  - 3  and N =7.0x10 c m v 1 8  Sze, 1981).  - 3  S u b s t i t u t i o n of  (A.2) t o (A.4) i n t o ( A . l ) y i e l d s  n n  2  2  + n(N -N.) - n. L_ + n(N - N - N ) - n . a d dd l 2  J  = -  N  e x p [ ( E -E )/kT] °  n  2  J J  (A.5)  Eq. (A.5) can then be s o l v e d f o r n (and p found from n^ =pn) and t h e 2  c o n d i t i o n s t o achieve s e m i - i n s u l a t i n g behaviour determined.  Johnson e t a l .  ( 1 9 8 3 ) , f o r example, have c o n s i d e r e d the case where N—11^=10 ^ c m  -  3  a r l (  j jr^_  E^,=Eg/2 and found t h a t s e m i - i n s u l a t i n g b e h a v i o u r ( i . e . 10 cm~" <n,p<10 c m ) 6  i s o b t a i n e d when  i s between 1.5x10 c m 1 5  - 3  and 5 x l 0 c m 1 8  - 3  3  8  - 3  which agrees w i t h  the EL2 c o n c e n t r a t i o n s measured by o p t i c a l a b s o r p t i o n by M a r t i n e t a l . ( l 9 8 l ) . The o r i g i n and c h e m i c a l n a t u r e of the EL2 l e v e l i s a s u b j e c t o f c u r r e n t debate.  A Ga d e f e c t i s b e l i e v e d t o be i n v o l v e d but i t i s not c l e a r  whether the d e f e c t c o n s i s t s of a s i n g l e Ga vacancy, a complex, o r an a n t i s i t e d e f e c t but t h e a s s o c i a t i o n of the l e v e l t o oxygen ( a l o n g h e l d b e l i e f ) has r e c e n t l y been d i s p r o v e d by Huber e t a l . ( 1 9 7 9 ) . EL2 i s an a r s e n i c a n t i s i t e d e f e c t , A S g  a  The p r e v a d i n g b e l i e f i s t h a t  (Lagowski e t a l . 1982).  I t has been found t h a t t h e r e s i s t i v i t y of LEC GaAs depends c r i t i c a l l y on melt c o m p o s i t i o n (Holmes et a l . , 1982). 0.51  I f an a r s e n i c f r a c t i o n of 0.48 t o  i s used, n type wafers of r e s i s t i v i t y above 10^ ton r e s u l t .  I f , however,  the a r s e n i c f r a c t i o n drops below 0.475 p type s u b s t r a t e s of much lower  87  r e s i s t i v i t y emerge.  These r e s u l t s a r e c o n s i s t e n t w i t h the t h e o r y t h a t i n a  As r i c h melt a l a r g e number of Ga v a c a n c i e s w i l l be p r e s e n t t e n d i n g t o f a v o u r EL2 f o r m a t i o n .  At h i g h a r s e n i c f r a c t i o n s , >0.52, a l a r g e c o n c e n t r a t i o n of  EL2 can be expected observed  result.  thus c a u s i n g a drop i n r e s i s t i v i t y which was  another  88  APPENDIX B - Some I o n I m p l a n t a t i o n Processes  A c t i v e L a y e r Implant Organization/ Reference Fujitsu  S p e c i e s Energy  Dose  Temp. Time  4.5x10  29 i  230  5.5x10  28 i  100  30 i  50  2.3x10  1 2  400  2.2x10  1 2  S i  Fabrication  Anneal  250  28  Used F o r GaAs MESFET  1 2  Comments Cap  850  15  850  30  Si0  2  850  30  Si0  2  800  20  Si0  2  850  30  S i 3 ^ - i m p l a n t i s done through 1100 A Si N layer.  Kitahara et a l . (1980) Hewlett-Packard  S  1 2  H o r n b u c k l e and Van T u y l (1981) Hughes  S  5x10^2  Maki e t a l . (1981) NEC  S  -1.6x10 c m dose i s used t o a c h i e v e enchancement d e v i c e s . 1 2  Furutsuka e t a l . (1981) Rockwell  Si  3  Welch e t a l . (1980)  Texas I n s t r .  2  1 +  -S 350KeV 1 0 c m n+ i m p l a n t used also. 1 3  28  850  S i  30  -capless proximity a n n e a l done.  Tserng e t a l . (1981) Westinghouse  29 i S  29S1  125 325  2x10 I 5x10  1 2  2  860  Si N 3  4  - i m p l a n t s done through 1000 A S i 3N1+ l a y e r .  Driver et a l . (1981)  - 2  89  APPENDIX C - Some Deep L e v e l s i n GaAs Detected by DLTS  Reference  [eV]  log a Association [cm ]  E E H H H H H  0.86 0.89 0.78 0.71 0.52 0.44 0.40  -13.5 -12.7 -15.3 -13.9 -15.5 -13.5 -12.7  H H H  0.58 0.64 0.44  -18.7 -15.4 -17.3  HL1 HL2  M4 M3 Ml  E E E  0.48 0.30 0.19  -12.6 -13.8 -13.3  EL4 EL7 EL10  ELI EL2 EL3 EL4 EL5 EL 6 EL7 EL8 EL9 EL10 EL11 EL12 ELI 4 EL15 EL16  E E E E E E E E E E E E E E E  0.78 0.825 0.575 0.51 0.42 0.35 0.30 0.275 0.225 0.17 0.17 0.78 0.215 0.15 0.37  -14.0 -12.9 -12.9 -12.0 -12.9 -12.8 -14.1 -14.1 -14.2 -14.7 -15.5 -11.3 -15.3 -12.2 -17.4  Bulk Epi Epi Epi Epi Bulk Epi Epi Epi Epi Epi Epi Bulk Epi Epi  HL1 HL2 HL3 HL4 HL5  H H H H H  0.94 0.73 0.59 0.42 0.41 .  -13.4 -13.7 -14.5 -14.5 -13.0  HL6 HL7 HL8  H H H  0.32 0.35 0.52  -13.3 -14.2 -15.5  Epi Epi Epi Epi Epi Epi Epi Epi  Label Electron/ Hole  Lang and Logan (1975) B  A Hasegawa et a l . (1975)  Lang et a l . (1976)  M a r t i n et a l . (1977)  Mitonneau et a l . (1977)  Em  Material  2  —  EL 2 HL1 HL2 HL3 HL4 HL5  —  Epi Epi Epi Epi Epi Epi Epi  (: L P E ) <I V P E ) (: L P E ) :LPE) <: L P E )  (; L P E ) (; L P E )  Cr l e v e l Cr l e v e l Fe l e v e l Cu l e v e l  E p i (; L P E ) E p i <: L P E ) EPI : L P E ) Epi Epi Epi  ;MBE) ;MBE) ;MBE)  :VPE) ;VPE) ^MBE) :VPE) :MBE) ^VPE) ;VPE) :MBE) :VPE) :VPE)  :VPE) ^VPE)  Cr l e v e l  (LPE) ;VPE) (VPE)  1; L P E ) (; V P E ) <;MBE) (;MBE)  Fe l e v e l Cu l e v e l  90  Reference  Label Electron/ Hole  Mitonneau et a l . (1977) cont'd  HL9 HL10 HL11 HL12  M a r t i n et a l . (1978)  S2 S3 S4 S5 SI S6  H H H H  Fairman et a l . (1979)  Zylbersztejn et a l . (1979)  H H  [eV]  log a Association [cm ]  0.69 0.83 0.35 0.27  -13.0 -12.8 -14.9 -13.9  0.74 0.57 0.35 0.34 0.80 0.27  -14.2 -12.3 -14.3 -13.6 -13.7 -13.7  0.48 0.48 0.35 0.22 0.75 0.55 0.55 0.46 0.34  -13.2 -11.2 -13.0 -14.7 -10.9 -14.2 -13.0 -12.7 -12.5  0.96 0.71  -12.8 -14.2  Erji  Material  2  J e r v i s et a l . (1979)  E p i (VPE) E p i (VPE) Bulk E p i (LPE) EL2 EL3 EL5 EL6 HL1 HL12  Bulk Bulk Bulk Bulk Bulk Bulk  (HB) (HB) (HB) (HB) (HB) (HB)  Bulk Bulk Bulk Bulk Epi Epi Epi Epi Epi  (HB) (HB) (HB) (HB) (VPE) (VPE) (VPE) (VPE) (VPE)  HL1 HL2  Epi Epi  (VPE) (VPE)  EL 2 HL2 HL5 EL2 HL2 HL3 HL4 HL5 HL7 EL7 HL1 HL3 HL5  E p i (LPE) E p i (LPE) E p i (LPE) E p i (implanted) E p i (implanted) E p i (implanted) E p i (implanted) E p i (implanted) E p i (implanted) Bulk (implanted) Bulk (implanted) Bulk (implanted) Bulk (implanted) Epi Epi  (VPE) (VPE)  Epi Epi Epi  (VPE) (VPE) (VPE)  EL3  I t o h and Yanai  0.75  -13.6  (1981)  0.61 0.94 0.62 0.41  -11.8  EL 2 EL3  -13.3 -14.1 -14.9  HL1 HL3 HL4  Reference Fairman et a l . (1981)  Label Electron/ Hole E H E E E H E H E E E H  Yuba e t a l . (1982)  Rhee et a l . (1982)  E H H H E E E H H  Em [eV]  log a Association [cm ]  0.26 0.30 0.34 0.51 0.65 0.90 0.15 0.30 0.34 0.60 0.65 0.90  -11.7 -13.2 -13.4 -12.0 -13.0 -13.7 -13.1 -13.2 -13.4 -12.0 -13.0 -13.7  0.88 0.54 0.48 0.34  -12.3 -12.9 -13.2 -12.4  0.90 0.85 0.73 0.17 0.52 0.17 0.21 0.84 0.15  -11.7 -12.9 -16.3 -21.4 -17.9 -22.3 -20.5 -12.9 -22.2  Material  2  HL1  Bulk Bulk Bulk Bulk Bulk Bulk Bulk Bulk Bulk Bulk Bulk Bulk  (HB) (HB) (HB) (HB) (HB) (HB) (LEC) (LEC) (LEC) (LEC) (LEC) (LEC)  ELI EL3 HL4 EL6  Bulk Bulk Bulk Bulk  (HB) (HB) (HB) (HB)  Bulk Bulk Bulk Bulk Bulk Bulk Bulk Bulk Bulk  (implanted) (implanted) (implanted) (implanted) (implanted)  HL12 EL6 EL4 HL1 HL12 EL6 EL3  

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.831.1-0095775/manifest

Comment

Related Items