Diffusion of antimony into silicon from an ion-bombarded layer
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OF
ION-BOMBARDED V. A .
ANTIMONY
INTO
SILICON
FROM
AN
LAYER
Panteleev
and
L.
N.
Isavtseva
UDC 537.226:539.219.3
R a d i o a c t i v e antimony was diffused into a s u r f a c e l a y e r of s i l i c o n . The b a s i c diffusive a n n e a l ing was c a r r i e d out a f t e r i r r a d i a t i o n with 2 9 104 p C / c m 2 of 55 keV h e l i u m ions. The i r r a d i a t i o n was found to s i g n i f i c a n t l y a c c e l e r a t e the diffusion. The r e s u l t s a r e d e s c r i b e d on the b a s i s of a m e c h a n i s m involving i n t e r s t i t i a l diffusion of antimony. Many t h e o r e t i c a l and e x p e r i m e n t a l s t u d i e s of diffusion in s e m i c o n d u c t o r s have been r e p o r t e d in r e c e n t y e a r s , but much r e m a i n s to be explained r e g a r d i n g the b a s i c m i c r o s c o p i c m e c h a n i s m f o r t h e s e p r o c e s s e s . One of the m o s t p r o m i s i n g d i r e c t i o n s f o r studying this p r o b l e m involves the study of diffusion in c r y s t a l s having v a r i o u s d e g r e e s of d e f e c t i v e n e s s , including those s u b j e c t e d to i r r a d i a t i o n [1, 2]. Shockley [2] p r o p o s e d such an e x p e r i m e n t in 1957. The idea behind this e x p e r i m e n t is that if a thin s u r f a c e l a y e r is c o n tinuously i r r a d i a t e d by m o d e r a t e - e n e r g y ions and s i m u l t a n e o u s l y doped at a high t e m p e r a t u r e by " s u b s t i t u t ing ~ e l e m e n t s (group III and V e l e m e n t s f o r Ge and Si), s o m e of the d e f e c t s i n t r o d u c e d will p e n e t r a t e into the s a m p l e and affect the dopant diffusion. Such e x p e r i m e n t s have been c a r r i e d out [4-6]; it has been found that the i r r a d i a t i o n s i g n i f i c a n t l y a c c e l e r a t e s the diffusion. This a c c e l e r a t i o n was a t t r i b u t e d in [4-6] to the p r e s e n c e of v a c a n c i e s (and d i v a c a n c i e s ) which a r e continuously g e n e r a t e d in the i r r a d i a t e d l a y e r and then m i g r a t e into the i n t e r i o r of the s a m p l e . Some r e s u l t s i m p l y i n g a d i f f e r e n t m e c h a n i s m for the a c c e l e r a t i o n of diffusion during i r r a d i a t i o n w e r e obtained in 1966 [7]. Silicon s a m p l e s w e r e h e a v i l y doped with r a d i o a c t i v e p h o s p h o r u s , so that s o m e of the p h o s p h o r u s n e a r the s u r f a c e was e l e c t r i c a l l y n e u t r a l (this s i t u a t i o n is u s u a l l y identified with i n t e r s t i t i a l p h o s p h o r u s ) . A f t e r the i r r a d i a t i o n of c e r t a i n s a m p l e s , this l a y e r with the n e u t r a l p h o s p h o r u s was r e m o v e d by etching. It turned out that in this c a s e the effect of i r r a d i a t i o n on the phosphorus diffusion was s i g n i f i c a n t l y s u p p r e s s e d . * This r e s u l t l e a d to the c o n c l u s i o n in [7] of a p o s s i b l e i n t e r s t i t
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