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PLASMA DIAGNOSTIC DURING THE GROWTH OF a-Si : H
T. Hamasaki, M. Hirose, Y. Osaka
To cite this version:
T. Hamasaki, M. Hirose, Y. Osaka. PLASMA DIAGNOSTIC DURING THE GROWTH OF a-Si : H. Journal de Physique Colloques, 1981, 42 (C4), pp.C4-807-C4-810. �10.1051/jphyscol:19814177�.
�jpa-00220802�
JOURNAL LIE PHYSlQUE
CoZZoque C4, suppliment uu no1O, Tome 4 2 , octobre 1981 page C4-807
PLASMA DIAGNOSTIC DURIEG THE GROWTH OF a - S i : H
T. Hamasaki, M . H i r o s e and Y . Osaka
Cepartmenl of l7lectricaZ r;?zgineering, Hiro.shima U n i v e r s i t y , Hiro:;nima 730, Japan
A b s t r a c t . - 'The o p t i c a l e m i s s i o n i n t e n s i t i e s o f t h e r e a c t i v e s p e c i e s , S i ( 2 8 8 nm), SiH (414 nm)
,
and I! (434, 4 8 6 , 656 nm) i n t h e s i l a n e p l a s m a w e r e mcas- u r e d a s f u n c t i o n s o f g a s f l o w r a t e and t o t a l p r e s s u r e . The r e l a t i v e c o n c e n - t r a t i o n s o f S i , SiH, a n d H r a d i c a l s h a v e b e e n c o r r e l . a t e d w i t h t h e g r o w t h r a t e , h y d r o g e n b o n d i n g , and i t s c o n t e n t f o r t h e r e s u l t i n g f i l m s . The d i f f u s i o n a l mass t r a n s p o r t o f t h e n e u t r a l r a d i c a l s , i n p a r t i c u l a r , t h e e m i s s i v e S i k l and 11, i s s u g g e s t e d t o h e r e s p o n s i b l e f o r t h e d e p o s i t i o n p r o c e s s o f a - S i : H .I n t r o d u c t i o n . - The p h y s i c a l p r o p e r t i e s o f amorphous h y d r o g c n a t e d s i l i c o n p r e p a r e d ----
by t h e glow d i s c h a r g e o f s i l a n e a r e s e n s i t i v e l y a f f e c t e d w i t h t h c p r o c e s s i n g c o n d i - t i o n s ; i . c . , t h c g a s f l o w r a t e , d i s c h a r g e power, and t o t a l p r e s s u r e c o u l d , i n g e n e r - a l , b e c o n n e c t e d w i t h t h e c o n c e n t r a t i o n s o f r e a c t i v e s p e c i e s , e l e c t r o n d e n s i t y , and e l e c t r o n temperature,respectively. A t t h e o r d i n a r y d e p o s i t i o n c o n d i t i o n s o f a-Si:H, c o n c e n t r a t i o n s o f n e u t r a l r e a c t i v e s p e c i e s a r e assumed t o b e a p p r e c i a b l y l a r g e com- p a r e d t o t h o s e o f i o n i c s p e c i e s [ I ] , b u t key c h e m i c a l s p e c i e s i n t h e p l a s m a a r e n o t i d e n t i f i e d y e t . Mass s p e c t r o a ~ e t r y [ l - 3 1 and o p t i c a l e m i s s i o n s p e c t r o s c o p y [4-61 a r e c u r r e n t l y u s e d t e c h n i q u e s f o r t h e d i a g n o s t i c s o f c h e s i l a n e p l a s m a . O p t i c a l e m i s s i o n s p e c t r o s c o p y w h i c h h a s d e m o n s t r a t e d t h e p r e s e n c e o f n e u t r a l r a d i c a l s s u c h a s S i , S i l l , H , and Hz, i s t h o u g h t t o h e a u s e f u l t o o l t o r e v e a l t h e b e h a v i o r s o f t h e r e a c t i v e s p e c i e s [ 7 ] .
E 3 e r i m e n t a l . - A s c h e m a t i c o f t h e e x p e r i m e n t a l a r r a n g e m e n t h a s b e e n r e p o r t e d e l s e -
.-
w h e r e [ 7 ] . The r e a c t o r was a v e r t i c a l q u a r t z t u b e w i t h a d i a m e t e r o f 6 0 mm, a n d t h e r f power was f e d t h r o u g h two e x t e r n a l r i n g e l e c t r o d e s . The g a s f l o w r a t e and p r e s s u r e w e r e i n d e p e n d e n t l y c o n t r o l l e d by a t h e r m a l mass f l o w c o n t r o l l e r and w i t h e x h a u s t c o n d u c t a n c e , r e s p e c t i v e l y . The m a g n e t i c f i e l d f o r c o n f i n i n g t h e p o s i t i v e column was a p p l i e d i n t h e d i r e c t i o n p e r p e n d i c u l a r t o t h e s u b s t r a t e s u r f a c e . O p t i c a l e m i s s i o n s p e c t r a from t h e s i l a n e d i s c h a r ~ e v c r c o b t a i n e d a s a c a l i b r a t e d photomul- t i p l i e r o u t p u t t h r o u g h a g r a t i n g monochromator w i t h a s l i t w i d t h o f 50 pm. The suh- s t r a t e t e m p e r a t u r e , c o n c e n t r a t i o n o f s i l a n e g a s , r f power, and m a g n e t i c f i e l d s t r e n g t h w e r e k e p t a t 300 O C , SiHt,/klz = 11 Z, 20 w a t t s , and 0 . 8 kG, r e s p e c t i v e l y .
R e s u l t s . - The o p t i c a l e m i s s i o n i n t e n s i t i e s o f t h e r e a c t i v e s p e c i e s S i ( 2 8 8 nm), SiH (414 nm), and It (656 nm) i n t h e s i l a n e p l a s m a w e r e m e a s u r e d a s a f u n c t i o n o f t h e t o t a l f l o w r a t e . R e l a t i v e c o n c e n t r a t i o n s o f t h e e m i s s i v e S i , S i H , and H h a v e b e e n d e t e r m i n e d from t h e o p t i c a l t r a n s i t i o n p r o b a b i l i t i e s [ 8 , 9 ] o f t h e c o r r e s p o n d i n g s p e c i e s . F i g u r e 1 shows t h e t o t a l f l o w r a t e d e p e n d e n c e o f t h e c o n c e n t r a t i o n s o f r e a c t i v c s p e c i e s i n t h e p l a s m a a t a c o n s t a n t g a s p r e s s u r e o f 0 . 6 4 T o r r . The con- c e n t r a t i o n o f t h e e m i s s i v e SiH i s two o r d e r s o f m a g n i t u d e l a r g e r t h a n t h a t o f t h e e m i s s i v e S i . The c u r v e f o r t h e c m i s s i v e H e x h i b i t s a peak a r o u n d 1 0 s c c m , s i g n i f i - c a n t l y d i f f e r e n t from t h e f l o w r a t e d e p e n d e n c e o f t h e 11 l i n e t a k c n f o r t h e p u r c hy- d r o g e n p l a s m a . T h i s s u g g e s t s t h a t a s i g n i f i c a n t amount of t h e e m i s s i . v e h y d r o g e n i s p r o d u c e d from t h e d e c o m p o s i t i o n o f S i l l ) , . F u r t h e r , t h e number o f t h e e x c i t e d s p c -
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19814177
C4-808 JOURNAL DE PHYSIQUE
c i e s measured a t d i f f e r e n t g a s p r e s s u r e s o f 0 . 5 , 1 , a n d 2 T o r r r e p r o d u c e d t h e flow- r a t e d c p e n d c n c e s i m i l a r t o t h e r e s u l t o f F i g . 1.
F i g u r e 2 shows t h e g a s p r e s s u r e d e p e n d e n c e o f t h e c o n c e n t r a t i o n s o f t h e r e a c - t i v e s p e c i e s a t a t o t a l f l o w r a t e o f 30 sccm. The b e h a v i o r o f t h e e m i s s i v e SiH is s i m i l a r t o t h a t o f S i , i n c o n s i s t e n c e w i t h t h e f a c t t h a t t h e e n e r g i e s r e q u i r e d t o p r o d u c e t h e e m i t t i n g s t a t e s o f SiH and S i a r e 8 . 9 and 9.5 eV, r e s p e c t i v e l y [ 5 ] . I t s h o u l d h e n o t e d t h a t t h e c o n c c n t r a t i o n o f a t o m i c h y d r o g e n a t a h i g h e r e n e r g y s t a t e Hy i s d r a m a t i c a l l y r e d u c e d w i t h a n i n c r e a s e o f g a s p r e s s u r e , b e c a u s e t h e e l e c t r o n t e m p e r a t u r e is l o w e r e d a s Lhe p r e s s u r e i n c r e a s e s a n d t h e n t h e f o r m a t i o n rate o f t h e e m i s s i v e Hy is a p p r e c i a b l y r c d u c e d compared t o t h a t o f t h e e m i s s i v e Ha a t a l o w e r e n c r g y s t a t e .
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TOTAL FLOW RATE (SCCM)
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x.2
: T o t a l f l o w - r a t e d e p e n d e n c e o f t h e c o n c e n t r a t i o n s o f r e a c t i v e s p e c i e s i n t h e p l a s m a a t a c o n s t a n t g a s p r e s s u r e o f 0 . 6 4 T o r r . Dashed c u r v e r e f e r s t o t h e e m i s s i v e h y d r o g e n Ha i n t h e p u r e h y d r o g e n p l a s m a u n d e r t h e same d i s c h a r g e c o n d i t i o n s .F i g . 2 : Gas p r e s s u r e d e p e n d e n c e o f t h e concentrations o f r e a c t i v e s p e c i e s a t a c o n s t a n t t o t a l f l o w - r a t e o f 30 sccm.
Each o f t h e c u r v e s is n o r m a l i z e d w i t h a v a l u e a t a g a s p r e s s u r e o f 0.5 T o r r .
The g r o w t h r a t e o f a-Si:H i n c r e a s e s w i t h f l o w r a t e , b u t i t i s l e s s d e p e n d e n t on g a s p r e s s u r e ( F i g . 3 ) . B a s i c a l l y , a-Si:H g r o w t h a p p e a r s t o b e l i m i t e d by t h e s i l a n e c o n c e n t r a t i o n i n g a s p h a s e a t low f l o w r a t e s , w h i l e r f power d o m i n a t e s t h e d e c o m p o s i t i o n r a t e a t h i g h f l o w r a t e s . The p r o d u c t o f t h e c o n c e n t r a t i o n s f o r t h e e m i s s i v e SiH and H [ S i H ] [ H ] m e a s u r e d a s a f u n c t i o n o f t o t a l f l o w r a t e i s a p p r o x i - m a t e l y p r o p o r t i o n a l t o t h e g r o w t h r a t e . I t is l i k e l y t h a t t h e c h e m i c a l r e a c t i o n SiH
+
H + S i+
H 2 o c c u r s o n t h e s u b s t r a t e s u r f a c e a n d / o r i n t h e g a s p h a s e .I
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F i g . 3 : T o t a l f l o w - r a t e dependence of t h e growth r a t e a t v a r i o u s g a s p r e s s u r e s and t h e p r o d u c t o f t h e r e a c t i v e SiH and H [SiH][H].
~b
2'0 3'04b 5bJ0
TOTAL FLOW RATE (SCCM)
The s t r e t c h i n g a b s o r p t i o n s p e c t r a f o r f i l m s p r e p a r e d a t d i f f e r e n t f l o w r a t e s a r e shown i n F i g . 4 ( a ) . The hydrogen c o n c e n t r a t i o n s i n c o r p o r a t e d i n t h e r e s u l t i n g f i l m s i n c r e a s e w i t h f l o w r a t e , and t h e peak p o s i t i o n of t h e s t r e t c h i n g a b s o r p t i o n moves from 2090 cm-' t o 2000 cm-'. T h i s i m p l i e s t h a t t h e c h e m i c a l r e a c t i o n between t h e SiH and H r a d i c a l s a d s o r b e d on t h e s u b s t r a t e s u r f a c e p r o d u c e s SiH2 u n i t s a t low flow r a t e s and d i r e c t i n c o r p o r a t i o n o f a d s o r b e d SiH i n t o t h e network o c c u r s a t h i g h f l o w r a t e s , b e c a u s e t h e c o n c e n t r a t i o n r a t i o o f SiH t o H i s n e a r two a t low f l o w r a t e s and a b o u t t e n a t h i g h f l o w r a t e s . The s t r e t c h i n g a b s o r p t i o n s p e c t r a f o r a-Si:,H f i l m s p r e p a r e d a t v a r i o u s g a s p r e s s u r e s a r e shown i n F i g . 4 ( b ) . The l i n e s h a p e of t h e s p e c t r a remains unchanged b u t t h e t o t a l hydrogen c o n t e n t d e c r e a s e s w i t h g a s p r e s s u r e from 2 1 t o 11 a t . % , s i n c e t h e s u r f a c e c o n c e n t r a t i o n of a t o m i c hydrogen i s reduced w i t h i n c r e a s e i n g a s p r e s s u r e ( s e e F i g . 2 ) . From t h i s r e s u l t and t h e f a c t
120C
TOW. FLYRATE 2 4 SCCM
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2F i g . 4 : S t r e t c h i n g a b s o r p t i o n s p e c t r a f o r a-Si:H f i l m s p r e p a r e d a t v a r i o u s t o t a l f l o w - r a t e s and a c o n s t a n t g a s p r e s s u r e of 0.64 T o r r ( a ) and f o r f i l m s d e p o s i t e d a t v a r i o u s g a s p r e s s u r e s and a c o n s t a n t f l o w - r a t e o f 30 sccm ( b ) .
C4-8 1 0 JOURNAL DE PHYSIQUE
t h a t t h e g r o w t h r a t e i s a l m o s t i n d e p e n d e n t o f g a s p r e s s u r e , t h e s u r f a c e c h e m i c a l r e a c t i o n SiH + S i
+
H a p p e a r s t o b e p r e d o m i n a n t a t h i g h p r e s s u r e s a n d t h e n t h e r e a c t i o n SiH+
H + S i+
H2 becomes l e s s i m p o r t a n t , b e c a u s e t h e c o n c e n t r a t i o n o f t h e e m i s s i v e H i s a p p r e c i a b l y r e d u c e d a n d t h e p a r t i a l p r e s s u r e o f Hz i n c r e a s e s w i t h g a s p r e s s u r e . As a r e s u l t , d e c r e a s e i n t h e g r o w t h r a t e d u e t o s u p p r e s s i o n o f r e - a c t i o n SiH+
H -+ S i+
Hz i s c o m p e n s a t e d by t h e o t h e r pathway SiH + S i+
H , w h i c h g i v e s r i s e t o a n e n h a n c e m e n t o f t h e g r o w t h r a t e .D i s c u s s i o n . - I m p o r t a n c e o f t h e r e a c t i v e SiH a n d H i s s u g g e s t e d f r o m a c o r r e l a t i o n b e t w e e n t h e c o n t e n t o f SiH2 u n i t s i n a-Si:H a n d t h e c o n c e n t r a t i o n r a t i o o f t h e e m i s s i v e SiH t o H i n t h e p l a s m a . F u r t h e r m o r e , The g r o w t h r a t e o f a-Si:H c o u l d b e i n t e r p r e t e d i n terms o f t h e r a d i c a l r e a c t i o n s s u c h a s S i l l
+
H + S i+
Hz a n dSiH + S i
+
H . S c o t t e t a l . [ l o ] e m p h a s i z e d t h e p o s s i b l e r e l e v a n c e o f SiH2 mole- c u l e s t o a-Si:H g r o w t h i n t h e p l a s m a from t h e i r k i n e t i c s t u d i e s o f new homogeneous CVD method. On t h e c o n t r a r y , we w o u l d s u g g e s t t h a t t h e SiH r a d i c a l i s r e s p o n s i b l e f o r t h e g r o w t h o f a-Si:H; i n t h e c o n v e n t i o n a l CVD t e c h n i q u e a t h i g h t e m p e r a t u r e s a b o v e 500 OC, SiH2 m o l e c u l e s p r o d u c e d i n t h e g a s p h a s e s h o u l d a d s o r b o n t h e s u b - s t r a t e , a n d t h e a d s o r b e d s t a t e o f SIR m o l e c u l e s i s c r e a t e d t h r o u g h t h e r e a c t i o n a s SiH2+
S i ( s o 1 i d ) + 2SiH. I n t h e c a s e o f g l o w d i s c h a r g e , c o n s i d e r a b l e amount o f SiH r a d i c a l s a r e o r i g i n a l l y p r e s e n t i n t h e p l a s m a , and t h e s t i c k i n g p r o b a b i l i t y o f t h e SiH r a d i c a l s may b e l a r g e r t h a n t h a t o f n e u t r a l SiHx ( x = 2, 3 ) m o l e c u l e s , i f e x i s t . T h e e m i s s i v e SiH i m p i n g i n g o n t h e s u b s t r a t e s u r f a c e c a n g i v e r i s e t o a-Si:H g r o w t h a s i n t h e c a s e o f CVD e v e n a t a t e m p e r a t u r e f a r b e l o w 500 "C. T u r b a n e t a l . [ I ] s t u d i e d t h e r e a c t i o n mechanism o f t h e Si11b(5 %)-H2 p l a s m a u s i n g mass s p e c t r o - m e t r y a n d p r o p o s e d t h a t t h e n e u t r a l r a d i c a l s SiHx (x = 2, 3 , 1 ) a r e t r a n s p o r t e d t o w a r d s w a l l and a t o m i c h y d r o g e n p l a y s a n i m p o r t a n t r o l e d u r i n g t h e d e p o s i t i o n o f a-Si:H. Kampas a n d G r i f f i t h [ 5 ] f o u n d t h a t t h e e m i s s i v e SiH i s p r o d u c e d d i r e c t l y f r o m t h e e x c i t e d s t a t e o f SiHk m o l e c u l e . T h e s e f i n d i n g s a r e e s s e n t i a l l y c o m p a t i b l e w i t h o u r i n t e r p r e t a t i o n . However a t t h e moment we c o u l d n o t g i v e a d e f i n i t e a n s w e rt o t h e q u e s t i o n ; w h i c h i s t h e k e y c h e m i c a l i n t e r m e d i a t e i n t h e p l a s m a , SiH, S i H 2 , o r S i H , .
I n c o n c l u s i o n , t h e n e u t r a l r a d i c a l s SiH a n d H a r e c a n d i d a t e d a s p o s s i b l e c h e m i c a l s p e c i e s r e s p o n s i b l e f o r a-Si:H g r o w t h f r o m t h e s i l a n e p l a s m a , a n d o p t i c a l e m i s s i o n s p e c t r o s c o p y c o u l d b e a u s e f u l t o o l t o r e v e a l t h e g r o w t h mechanism.
T h i s work was p a r t i a l l y s u p p o r t e d by t h e G r a n t - i n - A i d f o r S p e c i a l R e s e a r c h P r o g r a m "Amorphous M a t e r i a l s " g i v e n by t h e M i n i s t y o f E d u c a t i o n , R e s e a r c h and Cul- t u r e , t h e J a p a n e s e Government.
R e f e r e n c e s
1. TURBAN G., CATHERINE Y . , a n d GROLLEAU B . , T h i n S o l i d F i l m s
67
( 1 9 8 0 ) 309.2. DREVILLON B., HUC J . , LLRET A., PERRIN J . , DEROSNY G . , a n d SCHElITT J . P. M . , Appl. P h y s . L e t t .
37
(1980) 6 4 6 .3. HALLER I . , A p p l . P h y s . L e t t .
37
(1980) 282.4 . MATSUDA A., NAKAGAWA K., TANAKA K., MATSUMURA M . , YAMASAKI S . , OKUSHI H., a n d IIZIMA S . , J . Non-Cryst. S o l i d s
35-36
( 1 9 8 0 ) 1 8 3 .5. KAMPAS F. J . a n d GRIFFITH R. W . , J . A p p l . P h y s . i n p r e s s .
6. TANIGUCHI M . , HIROSE M . , HAMASAKI T . , and OSAKA Y . , A p p l . P h y s . L e t t .
37
(1980) 787.7. HIROSE M., HAMASAKI T . , MISHIMA Y . , KURATA H . , a n d OSAKA Y . , P r o c . o f T o p i c a l Conf. o n T e t r a h e d r a l l y Bonded Amorphous S e m i c o n d u c t o r s ( P h o e n i x , 1 9 8 1 ) , t o b e p u b l i s h e d .
8 . WIESE W. L . , SMITH M. h'., a n d MILES B. M., Atomic T r a n s i t i o n P r o b a b i l i t i e s ( N a t i o n a l S t a n d a r d R e f e r e n c e D a t a S y s t e m , W a s h i n g t o n , 1 9 6 9 ) , V o l . 1 p . 2 , V o l . 2 p.71.
9 . SMITH W. H., J . Chem. P h y s .
51
(1969) 520.1 0 . SCOTT B. A., PLECENIK R. M . , a n d SIMONY1 E. E . , t o b e p u b l i s h e d i n A p p l . P h y s . L e t t .
