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Role of surface migration in growth of Si films on Si substrate and on oxide layer
Volume29A, number 1
ROLE
PHYSICS
LETTERS
OF SURFACE MIGRATION ON Si SUBSTRATE AND
IN ON
24 March 1969
GROWTH OF Si OXIDE LAYER
FILMS
M. S A M O K H V A L O V , S. T A J I B A E V A a n d E. L E V S H I N The Moscow Institute of Steel and Alloys, Moscow, USSR Received 21 September 1968
The growth of Si film on the part of the s u b s t r a t e open to molecular beam was compared to the growth on the s c r e e n e d part. Etch pits were found to be p r e s e n t only on the open part. The dependence of growth figure density on vacuum, growth r a t e and c~ystallography of the substrate was investigated. When an oxide l a y e r was p r e s e n t in the open p a r t only etching took place, while in the s c r e e n e d part Si film continued to grow over the oxide.
W e i n v e s t i g a t e d i n i t i a l e p i t a x i a l g r o w t h of Si on Ge a n d Si in v a c u u m of 1 x 10-6 - 2 x 1 0 - 8 m m H g in t h e t e m p e r a t u r e r a n g e 6 0 0 - 1200°C. T h e s u b s t r a t e and s o u r c e w e r e h e a t e d d i r e c t l y by a.c. G r o w t h r a t e I - m a x . 10 # / / h o u r - w a s v a r i e d b y v a r y i n g the d i s t a n c e f r o m s u b s t r a t e to s o u r c e . P a r t of t h e s u b s t r a t e w a s s c r e e n e d . In a l l c a s e s g r o w t h f i g u r e s a n d e t c h p i t s d e v e l o p e d on t h e o p e n p a r t of t h e s u b s t r a t e ( f i g s . l a a n d 2). In t h e c o u r s e
Growth figures and etch pits on (111) Si substrate I = 3 × 10 -7 c m / s e c , T = 9 0 0 O c , t = 30 sec, x 2000.
Fig. 1. Growth figures and etch pits in the open (a) and s c r e e n e d (b) p a r t s of (100) Si substrate / = 3 ×10 -7 c m / sec, T = 800oc, t = 3 0 sec, x2000. 38
of t i m e f i g u r e s c o n t i n u e d to g r o w , a n d e t c h p i t s b e g a n to b e f i l l e d in. F o r t h i c k n e s s e s o v e r 0.5 # t h e f i l m s b e c a m e c o n t i n u o u s . In t h e s c r e e n e d p a r t (fig. l b ) t h e r e w e r e o n l y g r o w t h f i g u r e s , t h e d e n s i t y of w h i c h f e l l of w i t h t h e d i s t a n c e f r o m the boundary. While the d i f f e r e n c e in g r o w t h in b o t h p a r t s of t h e s u b s t r a t e w a s i n i t i a l l y s l i g h t , it a c c u m u l a t e d s o t h a t it w a s i m p o s s i b l e to p r o d u c e a c o n t i n u o u s f i l m i n t h e s c r e e n e d p a r t . If d e p o s i t i o n w a s d i s c o n t i n u e d ( s a y , f o r 10 s e c ,
Volume29A, number 1
PHYSICS LETTERS
by cutting off the b e a m ) and then r e s u m e d , the i nit i a l growth p i c t u r e was r e p e a t e d . By r e p e a t e d ly cutting the b e a m during d e p o s i t i o n it w a s p o s sible to i n c r e a s e f i l m t h i c k n e s s in the s c r e e n e d part. The d e n s i t y of growth f i g u r e s and etch p i t s w a s found to be dependent on: a) v a c u u m (1 x 106 c m - 2 at 1 x 10-6 m m Hg and 4 x 106 cm - 2 at 10 -7 to 2 x 10 -8 m m Hg); b) growth r a t e (1.5 x 106 c m - 2 at 1.2 x 10 -7 c m / s e c and 4 × 106 c m - 2 at 3 × x 10 -7 c m / s e c ) ; c) c r y s t a l l o g r a p h y of the subs t r a t e and l i t t l e dependent on t e m p e r a t u r e below ll00°C. A t h e o r y which i s the s u b je c t of the next l e t t e r w a s de v el o p ed to a c c o u n t for v a r i o u s a s p e c t s of the p r o c e s s . We have a l s o i n v e s t i g a t e d the growth in v a c u u m of Si on Si s u b s t r a t e p a r t l y c o v e r e d by t h e r m a l l y gr ow n SiO 2 f i l m 0.5 /~ thick. A s c r e e n p a r t l y c o v e r i n g Si and SiO 2 w a s p l a c ed o v e r the s u b s t r a t e . Vacuum w a s 1 x 10 -7 m m Hg, s u b s t r a t e t e m p e r a t u r e 900°C and d e p o s i t i o n r a t e 10 y / h o u r and t i m e - 6 c y c l e s of 1.5 rain d u r a t i o n with p a u s e s of 0.5 m i n inbetween. In the open p a r t SiO 2 f i l m i s d e s t r o y e d through i n t e r a c t i o n with i m p i n g i n g Si b e a m (as has been p r e v i o u s l y shown by J o y c e [1]). In the s c r e e n e d p a r t only the cool Si a t o m i c c o m p l e x e s a r e a b l e , a s a r e s u l t of m i g r a t i o n o v e r the Si s u r f a c e , to r e a c h SiO2, so the SiO 2 f i l m r e m a i n s intact. The r e s u l t a n t s t r u c t u r e i s shown on a m i c r o photograph (fig. 3). The o r i g i n a l Si-SiO2 boundary i s c l e a r l y v i s i b l e s i n c e it s e r v e d a s a n u c l e a t i o n l i n e f o r m i g r a t i n g Si. O v e r l a p p i n g t h i s boundary on the SiO 2 is a m o n o c r y s t a l l i n e Si band s o m e 10 ~t wide. The SiO 2 u n d e r this band i s shown by e t c h i n g away the Si f i l m e l e c t r o l y t i c a l l y , to be intact.
24 March 1969
Fig..3. Monocrystalline Si overgrowth on SiO2 film, I = 3 x 10 -7 cm/sec, T = 1000oc, t = 6 x 9 0 sec with stops of 30 sec. a) Thermally grown SiO2 film, b) Si film on SiO2 film, c) SiO2 film under Si film after it has been etched away, d) Si on the screened part of Si substrate, e) originial S i - SiO2 boundary, x 2000. The width of the band can be i n c r e a s e d by i n t e r m i t t e n t l y cutting the b e a m . Si c o m p l e x e s , a p p a r e n t l y , cannot m i g r a t e o v e r sioI. In the s a m e m a n n e r m o n o c r y s t a l l i n e f i l m p a t c h e s m ay f o r m around h o l e s in the u n o r i e n t e d f i l m , the total a r e a of such p a t c h e s depending upon the p r o c e s s and hole density. T h i s will r e sult in a m o r e o r l e s s p r o n o u n c e d m o n o c r y s t a i l i n e e l e c t r o n d i f f r a c t i o n p a t t e r n on a p o l y c r y s t a l l i n e o r a m o r p h o u s background.
1. B.A.Joyce et al. Phil. Mag. 15 No. 138 (1967).
39
ROLE
PHYSICS
LETTERS
OF SURFACE MIGRATION ON Si SUBSTRATE AND
IN ON
24 March 1969
GROWTH OF Si OXIDE LAYER
FILMS
M. S A M O K H V A L O V , S. T A J I B A E V A a n d E. L E V S H I N The Moscow Institute of Steel and Alloys, Moscow, USSR Received 21 September 1968
The growth of Si film on the part of the s u b s t r a t e open to molecular beam was compared to the growth on the s c r e e n e d part. Etch pits were found to be p r e s e n t only on the open part. The dependence of growth figure density on vacuum, growth r a t e and c~ystallography of the substrate was investigated. When an oxide l a y e r was p r e s e n t in the open p a r t only etching took place, while in the s c r e e n e d part Si film continued to grow over the oxide.
W e i n v e s t i g a t e d i n i t i a l e p i t a x i a l g r o w t h of Si on Ge a n d Si in v a c u u m of 1 x 10-6 - 2 x 1 0 - 8 m m H g in t h e t e m p e r a t u r e r a n g e 6 0 0 - 1200°C. T h e s u b s t r a t e and s o u r c e w e r e h e a t e d d i r e c t l y by a.c. G r o w t h r a t e I - m a x . 10 # / / h o u r - w a s v a r i e d b y v a r y i n g the d i s t a n c e f r o m s u b s t r a t e to s o u r c e . P a r t of t h e s u b s t r a t e w a s s c r e e n e d . In a l l c a s e s g r o w t h f i g u r e s a n d e t c h p i t s d e v e l o p e d on t h e o p e n p a r t of t h e s u b s t r a t e ( f i g s . l a a n d 2). In t h e c o u r s e
Growth figures and etch pits on (111) Si substrate I = 3 × 10 -7 c m / s e c , T = 9 0 0 O c , t = 30 sec, x 2000.
Fig. 1. Growth figures and etch pits in the open (a) and s c r e e n e d (b) p a r t s of (100) Si substrate / = 3 ×10 -7 c m / sec, T = 800oc, t = 3 0 sec, x2000. 38
of t i m e f i g u r e s c o n t i n u e d to g r o w , a n d e t c h p i t s b e g a n to b e f i l l e d in. F o r t h i c k n e s s e s o v e r 0.5 # t h e f i l m s b e c a m e c o n t i n u o u s . In t h e s c r e e n e d p a r t (fig. l b ) t h e r e w e r e o n l y g r o w t h f i g u r e s , t h e d e n s i t y of w h i c h f e l l of w i t h t h e d i s t a n c e f r o m the boundary. While the d i f f e r e n c e in g r o w t h in b o t h p a r t s of t h e s u b s t r a t e w a s i n i t i a l l y s l i g h t , it a c c u m u l a t e d s o t h a t it w a s i m p o s s i b l e to p r o d u c e a c o n t i n u o u s f i l m i n t h e s c r e e n e d p a r t . If d e p o s i t i o n w a s d i s c o n t i n u e d ( s a y , f o r 10 s e c ,
Volume29A, number 1
PHYSICS LETTERS
by cutting off the b e a m ) and then r e s u m e d , the i nit i a l growth p i c t u r e was r e p e a t e d . By r e p e a t e d ly cutting the b e a m during d e p o s i t i o n it w a s p o s sible to i n c r e a s e f i l m t h i c k n e s s in the s c r e e n e d part. The d e n s i t y of growth f i g u r e s and etch p i t s w a s found to be dependent on: a) v a c u u m (1 x 106 c m - 2 at 1 x 10-6 m m Hg and 4 x 106 cm - 2 at 10 -7 to 2 x 10 -8 m m Hg); b) growth r a t e (1.5 x 106 c m - 2 at 1.2 x 10 -7 c m / s e c and 4 × 106 c m - 2 at 3 × x 10 -7 c m / s e c ) ; c) c r y s t a l l o g r a p h y of the subs t r a t e and l i t t l e dependent on t e m p e r a t u r e below ll00°C. A t h e o r y which i s the s u b je c t of the next l e t t e r w a s de v el o p ed to a c c o u n t for v a r i o u s a s p e c t s of the p r o c e s s . We have a l s o i n v e s t i g a t e d the growth in v a c u u m of Si on Si s u b s t r a t e p a r t l y c o v e r e d by t h e r m a l l y gr ow n SiO 2 f i l m 0.5 /~ thick. A s c r e e n p a r t l y c o v e r i n g Si and SiO 2 w a s p l a c ed o v e r the s u b s t r a t e . Vacuum w a s 1 x 10 -7 m m Hg, s u b s t r a t e t e m p e r a t u r e 900°C and d e p o s i t i o n r a t e 10 y / h o u r and t i m e - 6 c y c l e s of 1.5 rain d u r a t i o n with p a u s e s of 0.5 m i n inbetween. In the open p a r t SiO 2 f i l m i s d e s t r o y e d through i n t e r a c t i o n with i m p i n g i n g Si b e a m (as has been p r e v i o u s l y shown by J o y c e [1]). In the s c r e e n e d p a r t only the cool Si a t o m i c c o m p l e x e s a r e a b l e , a s a r e s u l t of m i g r a t i o n o v e r the Si s u r f a c e , to r e a c h SiO2, so the SiO 2 f i l m r e m a i n s intact. The r e s u l t a n t s t r u c t u r e i s shown on a m i c r o photograph (fig. 3). The o r i g i n a l Si-SiO2 boundary i s c l e a r l y v i s i b l e s i n c e it s e r v e d a s a n u c l e a t i o n l i n e f o r m i g r a t i n g Si. O v e r l a p p i n g t h i s boundary on the SiO 2 is a m o n o c r y s t a l l i n e Si band s o m e 10 ~t wide. The SiO 2 u n d e r this band i s shown by e t c h i n g away the Si f i l m e l e c t r o l y t i c a l l y , to be intact.
24 March 1969
Fig..3. Monocrystalline Si overgrowth on SiO2 film, I = 3 x 10 -7 cm/sec, T = 1000oc, t = 6 x 9 0 sec with stops of 30 sec. a) Thermally grown SiO2 film, b) Si film on SiO2 film, c) SiO2 film under Si film after it has been etched away, d) Si on the screened part of Si substrate, e) originial S i - SiO2 boundary, x 2000. The width of the band can be i n c r e a s e d by i n t e r m i t t e n t l y cutting the b e a m . Si c o m p l e x e s , a p p a r e n t l y , cannot m i g r a t e o v e r sioI. In the s a m e m a n n e r m o n o c r y s t a l l i n e f i l m p a t c h e s m ay f o r m around h o l e s in the u n o r i e n t e d f i l m , the total a r e a of such p a t c h e s depending upon the p r o c e s s and hole density. T h i s will r e sult in a m o r e o r l e s s p r o n o u n c e d m o n o c r y s t a i l i n e e l e c t r o n d i f f r a c t i o n p a t t e r n on a p o l y c r y s t a l l i n e o r a m o r p h o u s background.
1. B.A.Joyce et al. Phil. Mag. 15 No. 138 (1967).
39