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HIGH VOLTAGE ELECTRON MICROSCOPY AND SCANNING ELECTRON MICROSCOPY (EBIC
MODE) OF THE SAME DISLOCATION
J. Heydenreich, H. Blumtritt, R. Gleichmann, H. Johansen
To cite this version:
J. Heydenreich, H. Blumtritt, R. Gleichmann, H. Johansen. HIGH VOLTAGE ELEC- TRON MICROSCOPY AND SCANNING ELECTRON MICROSCOPY (EBIC MODE) OF THE SAME DISLOCATION. Journal de Physique Colloques, 1979, 40 (C6), pp.C6-23-C6-26.
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H I G H VOLTAGE ELECTRON MICROSCOPY AND SCANN I N S ELECTRON MICROSCOPY
(EB
Ic
MODE) OF THE SAME D I S L O C A T I O N nJ. Heydenreich, H. a l u m t r i t t , R. Gleichmann and H. Johansen
I n s t i t u t fiir Festkiirperphysik m d EZektronenmikroskopie der Akademie der Wissenschaften der D. D. R., HaZZe/S. D. D.R.
Resume.- Les etudes des d e f a u t s c r i s t a l l i n s , specialement des d i s l o c a t i o n s s i t u s e s p r e s des j o n c t i o n s p-n formees au moyen de l a d i f f u s i o n dans des e c h a n t i l l o n s de s i l i c i u m , a i n s i que des d i s l o c a t i o n s s i t u e e s p r e s des j o n c t i o n s p-n i n d u i t e s p a r l e champ e l e c t r i q u e en des s t r u c t u r e s MIS s p e c i a l e s , q u i s o n t e f f e c t u e e s u t i l is a n t une combinaison : m i c r o s c o p i e e l e c t r o n i q u e
a
balayage (mode EBIC) e t m i c r o - s c o p i e e l e c t r o n i q u ea
haute t e n s i o n , o n t r e v e l 6 une c o r r e l a t i o n d i r e c t e e n t r e l e s d e f a u t s c r i s t a l l i n s i n d i v i d u e l s e t l e u r a c t i v i t e e l e c t r i q u e . Les r e s u l t a t s obtenus m o n t r e n t que p l u s c e t t e " a c t i v i t e " e s t grande, p l u s prononcge e s t l a " d e c o r a t i o n " des d e f a u t s p a r des agglomerations d ' i m p u r e t e s .A b s t r a c t . - I n v e s t i g a t i o n s o f c r y s t a l d e f e c t s , e s p e c i a l l y d i s l o c a t i o n s n e a r d i f f u s e d p-n j u n c t i o n s i n s i l i c o n m a t e r i a l s and n e a r f i e l d - i n d u c e d p-n j u n c t i o n s i n s u e c i a l MIS s t r u c t u r e s , c a r r i e d o u t b y a combination o f scanning e l e c t r o n microscopy (EBIC mode) and h i g h - v o l t a g e e l e c t r o n microscopy, have r e v e a l e d a d i r e c t c o r r e l a t i o n between i n d i v i d u a l c r y s t a l d ~ f e c t s and t h e i r e l e c t r i c a l a c t i v i t y . The achieved r e s u l t s p o i n t t o t h e f a c t t h a t t h i s " a c t i v i t y i s t h e h i g h e r t h e s t r o n g e r t h e imaged d e f e c t s a r e decorated by i m p u r i t y agglomerates.
1. I n t r o d u c t i o n .
-
The i n v e s t i g a t i o n o f t h e c o r r e l a- t i o n between d e f e c t s ( e s p e c i a l l y d i s l o c a t i o n s ) and e l c t r i c a l p r o p e r t i e s i n t e t r a h e d r a l l y c o o r d i n a t e d semi conductors, 1 i ke s i 1 ic o n o r germanium, presuppo- ses t h e combined a p p l i c a t i o n o f imaging methods f o r d e t e c t i n g t h e n a t u r e and arrangement o f c r y s t a l de- f e c t s as w e l l as i n t e g r a l e l e c t r i c a l measurements f o r d e t e r m i n i n g t h e i r i n f l u e n c e on a macroscopic sca- l e . A d i r e c t c o n n e c t i o n between m i c r o s c o p i c and ma- c r o s c o p i c parameters can be shown b y t h e use o f t h e scanning e l e c t r o n m i c r o s c o p i c (SEY) EBIC mode ( E l e c - t r o n Beam n d u c e d C u r r e n t and E l e c t r o n Beam n d u c e d C o n d u c t i v i t y , r e s p . ) , which g i v e s i n f o r m a t i o n b o t h-
on t h e presence o f i n d i v i d u a l c r y s t a l d e f e c t s and t h e i r e l e c t r i c a l a c t i v i t y , o f course w i t h a r e s t r i c - t e d l a t e r a l r e s o l u t i o n o f some microns /1,2/. So t h e combination o f t h e SEY (EBIC) t e c h n i q u e w i t h a h i g h e r r e s o l v i n g imaging method i s o f advantage /3-8/. I n t h e p r e s e n t i n v e s t i g a t i o n s t h e h i g h v o l t a g e e l e c t r o n microscopy (HVEM) was used as t h i s h i g h e r - r e s o l v i n g technique, on t h e one hand because o f i t s a b i l i t y o f t r a n s m i t t i n g t h i c k e r specimens (some m i c r o n s ) t h a n t h e c o n v e n t i o n a l t r a n s m i s s i o n e l e c t r o n microscope, so t h a t t h e a c h i e v a b l e statements w i t h r e s p e c t t o t h e c h a r a c t e r i z a t i o n o f t h e d e f e c t s a r e more r e p r e s e n t a - t i v e f o r t h e b u l k m a t e r i a l . On t h e o t h e r hand, t h e HVEM w i t h i t s f a c i l i t y o f a p p l y i n g a l a r g e - a r e a spe- cimen p r e p a r a t i o n /9/ o f f e r s good p o s s i b i l i t i e s
f o r t h e d i r e c t comparison w i t h SEM (EBIC) r e s u l t s . The method o f c r y s t a l d e f e c t imaging by u s i n g t h e SEY (EBIC) t e c h n i q u e (see e.g. / l o / ) i s based on t h e f a c t t h a t by t h e a c t i o n o f t h e e l e c t r o n probe 9 f t h e SEM e l e c t r o n - h o l e p a i r s a r e c r e a t e d i n a semiconduc- t i n g specimen, which u s u a l l y q u i c k l y recombine. I n r e g i o n s where a s u f f i c i e n t l y h i g h e l e c t r i c a l f i e l d i s p r e s e n t , e.g. a t a p-n j u n c t i o n o r a t a S c h o t t k y b a r r i e r , a s e p a r a t i o n o f e l e c t r o n - h o l e u a i r s i s rea- ched, t h u s g i v i n g a p o s s i b i l i t y f o r u s i n g t h e c r e a t e d c u r r e n t and c o n d u c t i v i t y , resp., f o r t h e f o r m a t i o n o f t h e SEM image. Present d e f e c t s i n t h e specimens i n f l u e n c e t h e recombination behaviour, i n s p e c i a l ca- ses a l s o t h e g e n e r a t i o n behaviour, o f t h e e l e c t r o n - h o l e p a i r s , so t h a t t h i s t e c h n i q u e g i v e s t h e p o s s i b i - l i t y f o r t h e
local
d e t e c t i o n o f t h i s d e f e c t - i n d u c e d r e c o m b i n a t i o n o r g e n e r a t i o n b e h a v i o u r o f t h e m a t e r i a l , i n each case under t h e assumption t h a t t h e a c t i n g d e f e c t s l i e n e a r a p-n j u n c t i o n o r a S c h o t t k y b a r r i e r . 2. Experimental and r e s u l t s . - The i n v e s t i g a t i o n s t o be d e s c r i b e d here which a r e r e l a t e d t o t h e d e t e c t i o n o f t h e " e l e c t r i c a l a c t i v i t y " o f d e f e c t s were c a r r i e d o u t f o r two d i f f e r e n t cases :I ) f o r d e f e c t s n e a r t h e p-n j u n c t i o n i n p-doped n- t y p e s i l i c o n m a t e r i a l s
11) f o r . d e f e c t s l y i n g i n a f i e l d - i n d u c e d p-n j u n c t i o n ( i n v e r s i o n l a y e r ) o f a s p e c i a l MIS s t r u c t u r e , which p r e f e r e n t i a l l y g i v e r i s e t o s o - c a l l e d m i -
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979605
C6-24 JOURNAL DE PHYSIQUE
croplasmas /11,12/.
The f i r s t k i n d o f i n v e s t i g a t i o n s was c a r r i e d o u t on (100) o r i e n t e d n - t y p e C z o c h r a l s k i s i l i c o n w i t h a r e s i s t i v i t y o f 5 Ohm cm, where t h e p-n j u n c t i o n was formed by boron d i f f u s i o n a t a depth o f 1.5 pm and t h e p - t y p e r e g i o n was covered w i t h a 0.6 pm t h i c k o x i d e l a y e r . The SEM (EBIC) i n v e s t i g a t i o n s were performed w i t h a JSY-U3 scanning e l e c t r o n microscope a t an a c c e l e r a t i n g v o l t a g e o f 15 kV (range o f prima- r y e l e c t r o n s : 2 pm). The HVEM i n v e s t i g a t i o n s were c a r r i e d o u t u s i n g a JEOL microscope, a t an a c c e l e r a - t i n g v o l t a g e o f 1009 kV.
F i g u r e 1 sho;us t h e comparison o f a SEM (EBIC) mi- crograph ( a ) and a HVEM micrograph ( b ) o f t h e same specimen r e g i o n . A s p e c i a l d i s l o c a t i o n c o n f i g u r a t i o n and a l s o a s t a c k i n g f a u l t can be r e c o g n i z e d i n b o t h micrographs. I n t h e SEV (EBIC) micrograph t h e i n - creased r e c o m b i n a t i o n b e h a v i o u r o f t h e c r y s t a l de- f e c t s , v i s i b l e f r o m t h e dark c o n t r a s t r e g i o n s ( d o t s
d i p o l e - 1 i ke c o n f i g u r a t i o n o f 60' d i s l o c a t i o n s w i t h 3 u r g e r s v e c t o r s =
+
a/2 C 1 1 0 1 .F i g . 2 : D e t a i l s o f f i g u r e 1 : TEV micrographs o f a d i s l o c a t i o n c o n f i g u r a t i o n (A) and a s t a c k i n g f a u l t
(B). I n s e t s : SEY (EBIC) micrographs and/or l i n e s ) r o u g h l y i n d i c a t e s t h e e l e c t r i c a l a c t i -
A s i m p l e s t e r e o a n a l y s i s c a r r i e d o u t by a l a r g e - a n g l e v i t y o f t h e d e f e c t s , e s p e c i a l l y w i t h r e s p e c t t o t r a n s -
t i l t i n g orocedure c o n f i r m e d t h a t t h o s e o a r t s o f t h e p o r t phenomena o f t h e m i n o r i t y charge c a r r i e r s . I n
d i s l o c a t i o n s which d i d n ' t g i v e d e t e c t a b l e c o n t r a s t t h e i n t e r p r e t a t i o n o f t h e m i c r o g r a ~ h s t h e p o s i t i o n
i n t h e EBIC m i c r o g r a p h ( c r o s s i n g d i s l o c a t i o n s : h o r i - o f t h e d e f e c t s , e s p e c i a l l y t h e i r d i s t a n c e f r o m t h e
z o n t a l one, upper p a r t o f v e r t i c a l one, d i p o l e - 1 i ke p-n j u n c t i o n , has t o be taken i n t o account, because
d i s l o c a t i o n s : l e f t - h a n d p a r t ) were l o c a t e d about o f t h e e x t r e m e l y low d i f f u s i o n l e n g t h s o f t h e charge
h a l f a m i c r o n below t h e p l a n e o f t h e p-n j u n c t i o n . c a r r i e r s o f o n l y 0.25 pm i n t h i s s p e c i a l l y chosen
The most i m p o r t a n t f e a t u r e i n t h i s m i c r o g r a p h i s t h e m a t e r i a l o f r e l a t i v e l y l a r g e i m p u r i t y c o n t e n t .
s t r o n g EBIC c o n t r a s t , which i s r e l a t e d t o t h e r i g h t
Fig. 1 : D i r e c t comparison o f s u r v e y micrographs o f d e f e c t s n e a r a s i l i c o n p-n j u n c t i o n , t a k e n i n t h e SEkI (EBIC) mode ( a ) and i n t h e h i g h - v o l t a g e e l e c t r o n microscope ( b )
.
T h i s i n f l u e n c e can be seen more c l e a r l y i n f i g u r e 2, where t h e r e g i o n s A and B o f f i g u r e 1 a r e shown i n h i g h e r m a g n i f i c a t i o n . A c c o r d i n g t o a d i f f r a c t i o n con- t r a s t a n a l y s i s t h e TEM micrograph o f t h e d i s l o c a t i o n arrangement A, g i v e n i n .the l e f t p a r t o f f i g u r e 2 shows two c r o s s i n g 60' d i s l o c a t i o n s w i t h Burgers vec- t o r s
Tf
= a/2C l i O l
f o r t h e v e r t i c a l one andTf
= a/2C l l O l
f o r t h e h o r i z o n t a l one and f u r t h e r m o r e aend o f t h e d i p o l e - l i k e d i s l o c a t i o n , where a more c a r e - f u l i n v e s t i g a t i o n r e v e a l e d a d e c o r a t i o n o f t h e d i s l o - c a t i o n c o n f i g u r a t i o n b y i m p u r i t y c l u s t e r s . T h i s f a c t o f s t r o n g EBIC c o n t r a s t f r o m r e g i o n s w i t h i m p u r i t y agglomerates, known a1 so f r o m l i t e r a t u r e (see e. g.
/13/) was found i n a l l i n v e s t i g a t i o n s c a r r i e d o u t . The r i g h t p a r t o f f i g u r e 2 ( r e g i o n B o f f i g u r e 1 ) shows an e x t r i . ~ s i c s t a c k i n g f a u l t l y i n g i n c l i n e d i n t h e ( 1 l i ) - p l a n e and h a v i n g a Burgers v e c t o r o f + b = a/3
Lii11.
T h i s s t a c k i n g f a u l t reaches a depth o f about 2.5 pm, so t h a t o n l y t h o s e p a r t s o f t h e s u r r o u n d i n g p a r t i a l d i s l o c a t i o n a r e imaged i n t h e EBIC m i c r o g r a p h (two d a r k s p o t s ) , w h i c h i n t e r s e c t t h e p l a n e o f t h e p-n j u n c t i o n . Again a d e c o r a t i n g e f f e c t o f t h e p a r t i a l d i s l o c a t i o n c o u l d be r e v e a l e d as t h e o r i g i n f o r t h e s t r o n g EBIC c o n t r a s t .I n v e s t i g a t i n g a m a t e r i a l o f h i g h e r o u r i t y , which g i v e s r i s e t o d i f f u s i o n l e n g t h s between 1 and 2 vm, i n t h e EBIC c o n t r a s t o f s t a c k i n g f a u l t s one can o f course see t h e whole s u r r o u n d i n g p a r t i a l d i s l o c a t i o n . T h i s i s shown i n f i g u r e 3 f o r s t a c k i n g f a u l t s rea- c h i n g a d e p t h o f about l pm ; t h e d e p t h o f t h e p-n j u n c t i o n b e i n g 1.7
urn
i n t h i s case. I n a d d i t i o n t ot h e EBIC m i c r o g r a p h ( l e f t p a r t ) t h e r e g i o n s A and B a r e shown more i n d e t a i l i n two HVEM micrographs.
F i g . 3 : SEN (EBIC) m i c r o g r a p h o f s t a c k i n g f a u l t s ( l e f t - h a n d s i d e ) and
-
f o r comparison-
d e t a i l s A, B i n t r a n s m i s s i o n e l e c t r o n micrographs.E s p e c i a l l y i n t e r e s t i n g a r e t h e c l o u d - l i k e c l u s t e r s a t some ends o f t h e s t a c k i n g f a u l t s , w h i c h c o u l d be i d e n t i f i e d 1141 t o c o n s i s t o f a l o o s e p a c k i n g of po- l y c r y s t a l l i n e s i l i c o n w i t h a r e l a t i v e l y h i g h c o n t e n t o f oxygen, n i t r o g e n and carbon. The h i g h EBIC con- t r a s t o f t h e s e r e g i o n s i s obvious ; i t must be men- t i o n e d , however, t h a t t h e r e a r e r e s u l t s which do n o t show t h i s ohenomenon.
The i n v e s t i g a t i o n s mentioned i n i t e m I 1 a r e c a r r i e d o u t on MIS s t r u c t u r e s based on n - t y p e C z o c h r a l s k i s i l i c o n w i t h a p - t y p e d i f f u s i o n r e g i o n w h i c h was co-
o
v e r e d by an o x i d e l a y e r o f about 1000 A t h i c k n e s s and
-
above t h i s-
by a metal e l e c t r o d e . A p p l y i n g a s u i - t a b l e n e g a t i v e v o l t a g e between t h e p - t y p e semiconduc- t i n g r e g i o n and t h e metal e l e c t r o d e , which i s h e l d on ground p o t e n t i a l , a f i e l d - i n d u c e d j u n c t i o n , t h i s means an n + - i n v e r s i o n l a y e r , i s formed j u s t beneath t h e o x i d e l a y e r , and c r y s t a l d e f e c t s l y i n g i n t h i s r e g i o n can be d e t e c t e d by EBIC c o n t r a s t and can be c o r r e l a t e d t o mi croplasma s i t e s . Because o f t h e appl i- c a t i o n o f a v o l t a g e t o t h e ' M I S s t r u c t u r e l o c a l h i g h - f i e l d r e g i o n s a r e produced a t t h e s i t e s o f c r y s t a l d e f e c t s ( d i s l o c a t i o n s ) and g i v e r i s e t o a charge c a r - r i e r m u l t i p l i c a t i o n w i t h an o p p o s i t e EBIC c o n t r a s t as i n t h e case o f l o c a l r e g i o n s o f enhanced recombi- n a t i o n . I n t a c t YIS s t r u c t u r e s o f t h i s t y p e show a w e l l - d e f i n e d breakdown v o l t a g e , i n t h e e l e c t r i c a l l y measured r e v e r s e c h a r a c t e r i s t i c s , w h i l e d e f e c t i v e MIS s t r u c t u r e s show a degraded ( s o f t ) c h a r a c t e r i s t i c . F i g u r e 4 g i v e s a comparison of SEM (EBIC) micrographs (a,c) and HVEY micrographs (b,d) o f an i n t a c t YISs t r u c t u r e (a,b) w i t h an i d e a l r e v e r s e c h a r a c t e r i s t i c and o f a d e f e c t i v e MIS s t r u c t u r e (c,d) w i t h a degra- ded r e v e r s e c h a r a c t e r i s t i c . No m i c r o p l asma s i t e s and no c r y s t a l d e f e c t s a r e p r e s e n t f o r t h e i d e a l case
(a,b). I n t h e case o f t h e d e f e c t i v e MIS s t r u c t u r e (c,d) microplasma s i t e s a r e v i s i b l e as b r i g h t - d a r k s p o t s i n t h e ( d i f f e r e n t i a t e d ) EBIC c o n t r a s t , and a d i r e c t c o r r e l a t i o n o f t h e microplasma s i t e s t o e x i s - t i n g c r y s t a l d e f e c t s , i n t h i s case s u r r o u n d i n g d i s - l o c a t i o n s o f s t a c k i n g f a u l t s , i s g i v e n .
Fig. 4 : D i r e c t comparison o f SEM (EBIC) micrographs (a,c) and HVEM micrographs ( b ,d) o f an i n t a c t (a, b ) and a d e f e c t i v e ( c , d ) MIS s t r u c t u r e .
I t must be mentioned, h o w e v e ~ t h a t t h e d e t e r m i n i n g f a c t i s n o t t h e number o f p r e s e n t d e f e c t s , b u t t h e i r t y o e , i n agreement w i t h i n v e s t i g a t i o n s c a r r i e d o u t by o t h e r methods (see e. g. 1 1 5 1 ) . Again t h e i n v e s t i g a t i o n s show t h a t t h e c r y s t a l d e f e c t i s t h e more e l e c t r i c a l l y a c t i v e t h e h i g h e r t h e i m p u r i t y a g g l o m e r a t i o n a t t h e d e f e c t . An example f o r t h i s i s g i v e n i n f i g u r e 5, which i s r e l a t e d t o an VIS s t r u c t u r e w i t h a v e r y bad r e v e r s e c h a r a c t e r i s t i c , a l t h o u g h o n l y one m i c r o p l a s - ma d e f e c t i s a c t i n g . The SEY (EBIC) /HVEV comparison
(a, b ) shows t h e r e l a t i o n of t h i s microplasma d e f e c t t o a s p e c i a l d i s l o c a t i o n c o n f i g u r a t i o n , which c o u l d be i d e n t i f i e d t o be o f p u r e edge c h a r a c t e r i n t h e m i d d l e p a r t and has a Burgers v e c t o r o f
$
= a/2[110].The most i m p o r t a n t p r o p e r t y i s t h e d e c o r a t i o n o f t h i l s d i s l o c a t i o n by i m ~ u r i t y c l u s t e r s . I n t h e r i g h t - h a n d s i d e t h e r e i s a g a i n a c l o u d - l i k e c l u s t e r r e g i o n o f p o l y c r y s t a l l i n e s i l i c o n w i t h i m p u r i t i e s , as d e s c r i b e d above. Besides t h i s oxygen p r e c i o i t a t e s (see e.g.
a t t h e crossed p o s i t i o n ) a r e p r e s e n t .
3. Conclusion.- The c o m b i n a t i o n o f t h e SEY (EBIC) t e c h n i q u e w i t h t r a n s m i s s i o n e l e c t r o n microscopy (es- p e c i a l l y HVEM) g i v e s r e l i a b l e statements on t h e e l e c - t r i c a l a c t i v i t y o f c h a r a c t e r i z e d i n d i v i d u a l c r y s t a l d e f e c t s .
C6-26 JOURNAL DE PHYSIQUE
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c i p i t a t i o n ) . So one has i n t e r c h a n g e a b l e processes. I n t h e d i f f i c u l t f i e l d o f f i n d i n g e x a c t c o n n e c t i o n s b e t - ween t h e t y p e o f a d i s l o c a t i o n and t h e process o f d e c o r a t i o n a l o t o f work has s t i l l t o be done. With r e s p e c t t o t h i s t h e weak-beam method s h o u l d be v e r y u s e f u l , e s p e c i a l l y f o r t h e i n v e s t i g a t i o n o f t h e s t a - t e o f d i s s o c i a t i o n o f t h e d i s l o c a t i o n s t o be r e g a r - ded / 1 6 / .
Acknowledgements.- The a u t h o r s a r e v e r y much i n d e b t e d t o P r o f . H. Bethge f o r h i s incouragement i n t h i s s t u d y and t o Mr. V. Seydewitz f o r c a r r y i n g o u t c o r r e s - ponding e l e c t r i c a l measurements.
