Silicon Detectors
Novel Detectors Sherwood Parker Chris Kenney
Nov. 6,1998
SLUO Lecture # 9
Silicon Detectors / Novel Detectors 1. a brief history of silicon detectors: challenges and turning points
2. the present challenge 3. a solution from micromachining:
3D
4. 3D fabrication, micromachining
5. results from the first fabrication runs 6. some future directions: a. thin detectors b. active edges
c. ....
1. history: 1962 - Wegner: surface barrier detectors 1964 - Madden: oxide passivation, diffused junctions 1966 - checker board counter (1.37 rnrn x,y strips) 1968 - ion implantation 4
Pixels, increased accuracy
1979 - Algranati, ... : charge transfer array detect. c--1979 - Kernrner: oxide passivation
+ ion implantation 1 output) 1982 - UCSB proposes SSVD for photoproduction
1983 - CERN/Hyams,.. ion imp./ox. pass., cap. chg. div. 6 strips / output for first SSVD experiment
1984 - finish fabrication of Microplex 1984 - Bailey, ..Hyams: CERN SSVD - first physics 1984 - Gatti, Rehak: silicon drift detector proposed 1985 - first beam tests results with Microplex 1985 - UCSB SSVD in (with non-VLSI electronics) 1985 - Hughes/SSRL/SLAC bump-bonded pixels 1986 - UCSB
-
first physics from US SSVD
1987 - monolithic pixels proposed 1988 - first collider SSVD ready (Microplex / Mark I1 / SLC) (installed 1989) 1990 - monolithic pixel fabrication complete 1991-2 - Fermilab tests: Hughes, monolithic pixels (monolithic: first ever < 2 pn 0)
+
1993 - SSC killed; LHC on; radiation levels higher
1996 - 3D proposed 1998 - 3D: first fabrication
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IEEE TRANSACTIONS ON NUCLEAR SCIENCE
UNIFORM AND STABLE dE/dx P-n JUNCTION PARTICLE DETECTORS T. C. Madden and W. M. Gibson B e l l Telephone Laboratories, Incorporated Murray H i l l , New J e r s e y S o l i d - s t a t e dE1dx.E p a r t i c l e i d e n t i f i c a t i o n systems r e q u i r e t h i n dE/dx d e t e c t o r s having a high tlegree of t h i c k n e s s uniformity. The l a c k of t h i s uniformity has been a I l m i t i n g f a c t o r i n achieving optimum results with t h e s e systems. I n a d d i t i o n , reproducible and s t r a i g h t f o r w a r d f a b r i c a t i o n techniques, long term s t a b i l i t y , and ruggedness are d e s i r e d f o r t h e r o u t i n e use of such devices. The w e of oxide s u r f a c e p a s s i v a t i o n , a planar-etching procedure, and a n improved back c o n t a c t have m d e p o s s i b l e t h e reproducible c o n s t r u c t i o n of t h i n , uniform, and s t a b l e diffused-junction p a r t i c l e d e t e c t o r s which meet t h e s e requirements. The response of t h e s e d e t e c t o r s t o b o t h p e n e t r a t i n g and nonpenetrating p a r t i c l e s , and t h e e f f e c t s of p a r t i c l e channeling through t h e c r y s t a l l a t t i c e are discussed.
INTRODUCTION Wegner1'2 has pointed out t h e p o t e n t i a l advantages i n t h e use of t h i n semiconductor d e t e c t o r s as transmission counters i n dE/dx.E p a r t i c l e i d e n t i f i c a t i o n systems. The f a b r i c a t i o n of both d i f f u s e d junction2,3,4 and s u r f a c e barrier5,6 s t r u c t u r e s f o r t h i s purpose has been r e p o r t e d . I n this work, devices were f a b r i c a t e d usiog a combination of phosphorus d l f f u s i o n , oxide p a s s i v a t i o n , and s u r f a c e barrier techniques. Thin transmission d e t e c t o r s p r e s e n t unusual f a b r i c a t i o n problems f o r two major reasons: (1) t h e t h i c k n e s s uniformity must be very good so t h a t s t a t i s t i c a l f l u c t u a t i o n s alone determine t h e energy spread of p a r t i c l e s p e n e t r a t i n g a t h i n d e t e c t o r ; and ( 2 ) t h e back c o n t a c t must block i n j e c t i o n t o avoid an i n c r e a s e i n t h e device noise when t h e space charge r e g i o n reaches t h e back. I n a d d i t i o n , t h e r e are t h e problems p r e s e n t with standard semiconductor d e t e c t o r s : long-term s t a b i l i t y , r e p r o d u c i b i l i t y of f a b r i c a t i o n , e t c . These p r o b l e m , i f anything, m e more severe f o r t h i n detectors. Several methods have been r e p o r t e d f o r making t h i n s i l i c o n wafers f o r use as G / d x d e t e c t o r s . These include conventional lapping and e t c h i n g techniques as used by Wegner2 and An&ews,5 and t h e more s o p h i s t i c a t e d techniques of Inskeep, Edison and LBSalle3 and E l l i o t and Pehl.4 Howe v e r , a p l a n a r - e t c h i n g system was a v a i l a b l e which showed promise of producing t h i n s i l i c o n wafers which were more uniform and of l a r g e r area t h a n those p r e v i o u s l y r e p o r t e d . I n a d d i t i o n , it was f e l t t h a t t h e use of s i l i c o n dioxide s u r f a c e p a s s i v a t i o n 7 could o f f e r
s p e c i a l advantages f o r t h i n d e t e c t o r s . k s i d e s junction edge p r o t e c t i o n , t h e p l a n a r s t r u c t u r e (1)t h e provides two a d d i t i o n a l advantages: oxide f i l m l e n d s s t r e n g t h t o t h e device; and ( 2 ) t h e use of t h e oxide f i l m f o r d i f f u s i o n masking removes t h e n e c e s s i t y of forming a mesa s t r u c t u r e . A blocking s u r f a c e - b a r r i e r back contact of t h e type described by Andrews5 was f e l t t o be t h e most e f f e c t i v e c u r r e n t s o l u t i o n t o t h e problem of electron injection.
One problem which was a n t i c i p a t e d b u t which d i d not p r e s e n t any s p e c i a l d l f f i c u l t y w a s t h a t of devlce breakage due t o t h e b r i t t l e n e s s of t h i n s i l i c o n . Thin d e t e c t o r s n a t u r a l l y r e q u i r e more c a r e f u l handling than conventional devices, b u t they need not be f r a g i l e or b r i t t l e . With sawing and lapping d-ge removed, s i l i c o n i s extremely strong, and i n t h e case of s e c t i o n s a s t h i n as 1 mil, f l e x i b l e .
DEVICE FABRICATION
Preparation of Silicon The lapped s i l i c o n wafer from which a t h i n d e t e c t o r i s made must be very uniform i n t h i c k ness, s i n c e t h e f i n a l device can be no more uniform t h a n t h e o r i g i n a l wafer. I n t h i s work t h e s i l i c o n wafers were lapped on a b i s u r f a c e p l a n e t a r y lapping machine using 3034 A1203 abrasive which l e f t t h e f i n i s h e d wafers with To i n s u r e thickness v a r i a t i o n of 0.01 removal of s t r u c t u r a l damage r e s u l t i n g from t h e sawing and lapping operations, 3 mils were etched from each s i d e of t h e s e wafers.
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