OBSERVATION OF INDIVIDUAL MISFIT DISLOCATIONS BY HIGH-VOLTAGE ELECTRON MICROSCOPY

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OBSERVATION OF INDIVIDUAL MISFIT

DISLOCATIONS BY HIGH-VOLTAGE ELECTRON MICROSCOPY

H. Strunk, W. Hagen, B. Kolbesen

To cite this version:

H. Strunk, W. Hagen, B. Kolbesen. OBSERVATION OF INDIVIDUAL MISFIT DISLOCATIONS

BY HIGH-VOLTAGE ELECTRON MICROSCOPY. Journal de Physique Colloques, 1979, 40 (C6),

pp.C6-213-C6-216. �10.1051/jphyscol:1979642�. �jpa-00219058�

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JOURNAL DE PHYSIQUE CoZZoque CF, suppl6ment au n06, tome 4 0 , juin 1979, page C6-213

OBSERVATION OF I N D I V I D U A L M I S F I T DISLOCATIONS BY HIGH-VOLTAGE ELECTRON MICROSCOPY

H. s t r u n k x , W . ~ a ~ e n ' " and B.O. ~olbesen'**

x i ~ m - ~ ~ u n c k I n s t i t u t fiir MetaZZforschung, Heisenbergstr. 1 , 7000 Scuttgart-83, Germany Max-PZrmck I n s t i t u t fiir Festkiiperforschung, Heisenbergstr. 1 , 7000 Stuttgmt-80, Germany

"'Siemens AC, ilnternehensbereich BaueZemente, Balanstr. 75, 8000 Miinchen 80, Germany

Resume.- Les d i s l o c a t i o n s d ' i n t e r f a c e s q u i se p r o d u i s e n t apres e p i t a x i e ou d i f f u s i o n dans l e s semi- conducteurs sont e t u d i e e s p a r m i c r o s c o p i e e l e c t r o n i q u e

a

h a u t e t e n s i o n . Les e c h a n t i l l o n s s o n t p r e - pares en u t i l i s a n t une technique d'amincissement s u r de grandes s u r f a c e s . Les o b s e r v a t i o n s a i n s i e f f e c t u e e s montrent l ' i n f l u e n c e de l a s u r f a c e l i b r e e t de l ' e x t e n s i o n l a t e r a l e des i n t e r f a c e s s u r l e s d i s l o c a t i o n s .

A b s t r a c t . - I n d i v i d u a l m i s f i t d i s l o c a t i o n s i n e p i t a x i a l and d i f f u s i o n a l i n t e r f a c e s o f semiconducting m a t e r i a l s a r e i n v e s t i g a t e d by h i g h - v o l t a g e e l e c t r o n microscopy u s i n g l a r g e - a r e a t h i n n e d specimens.

The o b s e r v a t i o n s show t h e p a r t i c u l a r i n f l u e n c e o f t h e s u r f a c e and o f t h e l a t e r a l dimensions o f t h e i n t e r f a c e on t h e s e m i s f i t d i s l o c a t i o n s .

1. I n t r o d u c t i o n . - M i s f i t d i s l o c a t i o n a r r a y s a r e a common f e a t u r e o f i n t e r f a c e s produced by h e t e r o e p i - t a x y o r b y d i f f u s i o n o f s o l u t e atoms. The d i s l o c a - t i o n s form t o r e l e a s e t h e s t r a i n o f a d j a c e n t c r y s t a l r e g i o n s h a v i n g d i f f e r e n t l a t t i c e parameters ( m i s f i t ) . According t o e n e r g e t i c a l assessments f o r a p l a n a r , p r a c t i c a l l y i n f i n i t e , i n t e r f a c e t h e i n t r o d u c t i o n o f d i s l o c a t i o n s i n t o a s p e c i f i c i n t e r f a c e becomes ener- g e t i c a l l y f a v o u r e d beyond a c r i t i c a l t h i c k n e s s o f

<he e p i l a y e r / I / . I n t h e case o f d i f f u s i o n , t h i s t h i c k n e s s corresponds t o a c r i t i c a l " i n t e g r a t e d excess c o n c e n t r a t i o n o f s o l u t e atomsn (e.g. / 2 / ) which can be c o n v e r t e d i n t o a c r i t i c a l s u r f a c e con- c e n t r a t i o n f o r a g i v e n d i f f u s i o n p r o f i l e . The e x p e r i - mental c o n d i t i o n s , such as c r y s t a l s t r u c t u r e , o r i e n - t a t i o n , and temperature, determine whether m i s f i t d i s l o c a t i o n s a c t u a l l y f o r m o r n o t and what t y p e of a r r a y s develop. A c c o r d i n g l y d i f f e r e n t b a s i c forma- t i o n processes have been suggested : ( i ) g l i d e o f t h r e a d i n g (grown-in) d i s l o c a t i o n s /3/, ( i i ) nuclea- t i o n o f g l i d e d i s l o c a t i o n s a t t h e s u r f a c e /4/, and ( i i i ) c l i m b o f d i s l o c a t i o n s by agglomeration o f a t o - m i c d e f e c t s /5/.

The d e t a i l e d i n v e s t i g a t i o n o f i n i t i a l processes i n t h e f o r m a t i o n o f m i s f i t d i s l o c a t i o n s b y e l e c - t r o n microscopy was impeded i n t h e p a s t due t o p r e - p a r a t i o n problems; t h e c o n v e n t i o n a l p r e p a r a t i o n techniques c o u l d n o t p r o v i d e f o i l s c o n t a i n i n g t h e p l a n a r d i s l o c a t i o n a r r a y s always j u s t i n t h e small t r a n s m i t t a b l e areas. Thus a r r a y s w i t h h i g h m i s f i t d i s l o c a t i o n d e n s i t i e s have been i n v e s t i g a t e d o n l y k h i c h are, however, d i f f i c u l t t o a n a l y z e w i t h r e s p e c t t o i n i t i a l f o r m a t i o n mechanisms o r d i s l o c a t i o n reac- t i o n s .

A few y e a r s ago a l a r g e - a r e a t h i n n i n g t e c h n i - que has been developed f o r semiconducting wafers and devices /6/. T h i s t e c h n i q u e y i e l d s m e c h a n i c a l l y s t a - b l e specimens w i t h a u n i f o r m t h i c k n e s s o f s e v e r a l pm over areas o f s e v e r a l m2, which a r e t r a n s p a r e n t i n a h i g h - v o l t a g e e l e c t r o n microscope. The b e n e f i t o f such specimens f o r t h e i n v e s t i g a t i o n o f c r y s t a l l i n e d e f e c t s o c c u r r i n g i n v e r y l o w d e n s i t y has been amply demonstrated / 7 - l o / . I n t h e f o l l o w i n g s e l e c t e d obser- v a t i o n s on m i s f i t d i s l o c a t i o n s a r e r e p o r t e d which i n general c o r r o b o r a t e t h e b a s i c g e n e r a t i o n models men- t i o n e d above. The examples s h a l l demonstrate, how s u r f a c e and f i n i t e s i z e o f t h e considered " m i s f i t - i n g " r e g i o n i n f l u e n c e t h e b e h a v i o u r o f t h e i n i t i a l generated m i s f i t d i s l o c a t i o n s .

2. Observations and discussion.- 2.1. igfrtgence-gf surface.- F i g u r e 1 shows a s e c t i o n o f t h e rectangu-

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l a r m i s f i t d i s l o c a t i o n network c o n s i s t i n g o f 60' d i s l o c a t i o n s , which a r e formed i n t h e ( 0 0 1 ) - i n t e r - f a c e between t h e Ge e p i t a x i a l overgrowth and GaAs s u b s t r a t e

/ l o / .

A t A t h e c r o s s i n g o f d i s l o c a t i o n s w i t h i d e n t i c a l Burgers v e c t o r s l e d t o a l o c a l a n n i - h i l a t i o n r e s u l t i n g i n t h e f o r m a t i o n o f two a n g u l a r d i s l o c a t i o n s ( d i s l o c a t i o n s 1 and 2 ) . As shown r e - c e n t l y /11/, one o f t h e s e a n g u l a r d i s l o c a t i o n s g l i - des towards t h e s u r f a c e under t h e a c t i n g image f o r - ces ( d i s l o c a t i o n 1 ) . By i n t e r s e c t i n g t h e s u r f a c e ( F i g u r e 1, c o n f i g u r a t i o n B ) two independent d i s l o c a - t i o n segments a r e c r e a t e d t h a t a r e capable o f t r a i - l i n g f u r t h e r m i s f i t d i s l o c a t i o n s . This source i s n o t r e s t r i c t e d t o t h e ( 0 0 1 ) - o r i e n t a t i o n n e i t h e r t o an e p i t a x i a l s t r u c t u r e . T h i s f a c t i s demonstrated i n f i g u r e 2, which shows a p a r t o f a b o r o n - d i f f u s e d e m i t t e r o f a b i p o l a r t r a n s i s t o r f a b r i c a t e d on a

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979642

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C6-2 14 JOURNAL DE PHYSIQLE

( 1 1 1 ) - o r i e n t a t e d wafer. The 60'-dislocations l i e along <110> d i r e c t i o n s and have s l i p p e d on o b l i q u e Ell11 planes i n t o a plane p a r a l l e l t o the d i f f u s i o n f r o n t . C marks a c o n f i g u r a t i o n analogous t o t h a t i n f i g u r e 1 a t A; stereo micrographs show t h a t t h e t i p a t 1 deviates from the general plane made up by t h e d i s l o c a t i o n s and i s l i a b l e t o t h e proposed source mechanism.

F i g . 1 : Rectangular a r r a y o f 60' m i s f i t d i s l o c a t i o n s a t the i n t e r f a c e o f t h e system Ge on GaAs. I n t e r f a c e

= (001). : d i f f r a c t i o n vector. A,B : see F i g . 2 : D e t a i l o f the a r r a y o f m i s f i t d i s l o c a t i o n s t g x t . microgra~hs shown are taken approximately i n a boron-diffused e m i t t e r .

n

⁼(111). C : see t e x t . p a r a l l e l t o t h e i n t e r f a c e s . (Granular s t r u c t u r e o f surface due t o e t c h i n g ) .

F i g . 3 : a) D e t a i l of a m i s f i t d i s l o c a t i o n a t t h e boundary BE of-a boron-diffused e m i t t e r E.

n

⁼^(111).

b) G l i d e process proposed f o r i t s formation. Normals (111) and (111) p o i n t towards t h e reader.

2.2.

Influgncg-of-jateya1-bggn_dg~je~ .-

F i g u r e 3a However, a shear s t r e s s may s t i l l a c t i n the (111)- shows a c o n f i g u r a t i o n o f a m i s f i t d i s l o c a t i o n f r e - plane which causes the screw segment ( p o s i t i o n 2), q u e n t l y observed a t the l a t e r a l boundaries o f the a f t e r c r o s s - s l i p , t o g l i d e again across the diffused j u s t considered e m i t t e r s . T h i s d i s l o c a t i o n has been zone ( p o s i t i o n 3 ) . The f r e q u e n t r e p e t i t i o n o f t h i s t r a i l e d v e r y l i k e l y by a d i s l o c a t i o n segment t h a t " r e f l e c t i o n " , aided by a "favourable" geometry o f t h e s l i p p e d under t h e i n f l u e n c e o f stresses a t t h e d i f f u s e d zone, leads t o an e f f e c t i v e p r o d u c t i o n o f e m i t t e r boundary as depicted i n f i g u r e 3b. Upon m i s f i t d i s l o c a t i o n s i n a l a t e r a l l y l i m i t e d i n t e r f a c e approaching the boundary, the g l i d i n g d i s l o c a t i o n by one S i n g l e d i s l o c a t i o n segment only. Such a pro- segnent 1 comes t o r e s t , say a t p o s i t i o n 2, where the cess i s undesired i n device technology because t h e shear s t r e s s a c t i n g i n t h e ( i l l ) g l i d e plane i s e l e c t r i c a l c h a r a c t e r i s t i c s o f p-n j u n c t i o n s are de- approximately z e r o due t o t h e decreasing m i s f i t . t r i m e n t a l l y i n f l u e n c e d by d i s l o c a t i o n s . I n t h e pre-

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H.. Strunk. e.t al. Ch-215

sent case, an a p p r o p r i a t e l y chosen geometry c o u l d p l i c a t i o n may be induced due t o t h e stresses a r i s i n g h e l p t o reduce t h e frequency o f " r e f l e c t i o n s " . from t h e boundaries. The suppression o f Such mecha-

If no g l i d e d i s l o c a t i o n s are present, edge nisms i s important f o r device technology and m i g h t d i s l o c a t i o n s a r e f r e q u e n t l y formed by climb t o r e - be p o s s i b l e by a proper choice of t h e geometries of lease t h e m i s f i t s t r e s s . These d i s l o c a t i o n s are most the v a r i o u s doped regions.

e f f i c i e n t i n t h e r e l a x a t i o n o f the m i s f i t s t r a i n and do n o t g l i d e g e n e r a l l y . However, they can be a c t i v a - t e d as d i s l o c a t i o n sources by a d d i t i o n a l stresses.

Such an a c t i v a t i o n occurs v e r y l i k e l y i n a narrow

" m i s f i t t i n g " r e g i o n i n which the boundary area i s dominant. One i l l u s t r a t i n g example s h a l l be e x p l a i - ned w i t h t h e a i d o f f i g u r e 4. Figure 4a shows p a r t o f a t r a n s i s t o r contained i n a memory device The c o l l e c t o r contacts o f these t r a n s i s t o r s g e n e r a l l y contained m i s f i t d i s l o c a t i o n s introduced by c l imb due t o t h e h i g h phosphorus-concentration. Disloca- t i o n s confined t o the c o l l e c t o r - c o n t a c t area d i d n o t a f f e c t t h e e l e c t r i c a l p r o p e r t i e s o f t h e t r a n s i s t o r s . However, i n almost a l l o f t h e t r a n s i s t o r s t h a t showed a c o l l e c t o r - e m i t t e r short, t h e e m i t t e r con- t a i n e d d i s l o c a t i o n s a l s o . Contrast experiments r e - vealed t h a t i n many t r a n s i s t o r s the d i s l o c a t i o n s i n t h e e m i t t e r posessed t h e same s u r f a c e - p a r a l l e l Bur- gers v e c t o r as those i n t h e c o l l e c t o r c o n t a c t . These r e s u l t s suggest t h a t t h e d i s l o c a t i o n s i n the e m i t t e r have been e m i t t e d from t h e c o l l e c t o r - c o n t a c t . The process may be v i s u a l i z e d as sketched i n f i g u r e 4b.

I n the r e l a t i v e l y small area o f the c o n t a c t a c l i m - bed-in d i s l o c a t i o n e x h i b i t s steep segments which can be recognized i n stereomicrographs o r by t h e i r Pen- dellcsung c o n t r a s t (see S i n f i g u r e 4a). Such a d i s l o c a t i o n segment may, over a c e r t a i n length, l i e i n one o b l i q u e I1111 plane c o n t a i n i n g i t s Burgers v e c t o r ( p o s i t i o n 1 i n f i g u r e 4b). A shear s t r e s s component exerted by t h e surface c o a t i n g (e.g. s i - l i c o n d i o x i d e o r - n i t r i d e ) o r due t o t h e shape o f t h e d i f f u s e d area may f o r c e t h i s d i s l o c a t i o n l e n g t h t o g l i d e and t o leave t h e c o n t a c t area; even a s i n - g l e ended source mechanism can be a c t i v a t e d ( F i g - 4b a t 2 and 3 ) .

I t should be noted t h a t the s p a t i a l shape o f v a r i o u s d i s l o c a t i o n s i n t h e contacts c o u l d n o t be understood i n terms o f c l i m b and o f g l i d e on I l l l l - t y p e planes only. Probably l i m i t e d g l i d e on o t h e r low i n d i c e s planes was involved, which appears p o s s i b l e under extreme c o n d i t i o n s /12/.

3. Conclusions.- The presented d i s l o c a t i o n arran-

gements show t h a t m i s f i t d i s l o c a t i o n s are i n f l u e n c e d Fig. : a) Part of bipolar transistor. CC : Col.lec- by t h e c r y s t a l l o g r a p h i c o r i e n t a t i o n and t h e geome- t o r contact, E : e m i t t e r .

n

⁼(001).

t r i c a l dimensions o f t h e i n t e r f a c e . E s p e c i a l l y i n b) Suggested mechanism o f d i s l o c a t i o n g l i d e r e s u l t i n a from a climbed-in d i s l o c a t i o n .

M

: 90' small-area i n t e r f a c e s a d d i t i o n a l d i s l o c a t i o n m u l t i - m i s f i t d i s l o c a t i o n ,

2 I

Burgers v e c t o r .

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C6-2 16 JOURNAL DE PHYSIQUE

Acknowledgement.- P a r t of t h i s work was supported by t h e Federal Department of Research and Technology o f the Federal Republic of Germany.

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