RF POWER AND TEMPERATURE DEPENDENCES IN GD a-Si PRODUCED FROM HEATED SiH4

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RF POWER AND TEMPERATURE DEPENDENCES IN GD a-Si PRODUCED FROM HEATED SiH4

S. Hasegawa, Y. Kurata, Y. Imai, S. Narikawa

To cite this version:

S. Hasegawa, Y. Kurata, Y. Imai, S. Narikawa. RF POWER AND TEMPERATURE DEPEN-

DENCES IN GD a-Si PRODUCED FROM HEATED SiH4. Journal de Physique Colloques, 1981, 42

(C4), pp.C4-675-C4-678. �10.1051/jphyscol:19814149�. �jpa-00220771�

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CoZZoque C4, suppl6ment au nOIO, Tome 42, octobre 1981 page C4-675

R F POWER AND TEMPERATURE DEPENDENCES I N GD a - S i PRODUCED FROM HEATED S i H 4

S. Hasegawa, Y. K u r a t a , Y. I m a i and S . N a r i k a w a

Department o f EZectronics, Kanazma Uniuersi t y , Ka~zazawa 920, Japan

A b s t r a c t . - The r e l a t i o n s h i p s b e t w e e n e l e c t r i c a l p r o p e r t i e s , ESR. I R a n d o p t i - c a l a b s o r p t i o n a r e i n v e s t i g a t e d f o r r f glow d i s c h a r g e S i f i l m s p r o d u c e d from SiH4/H2 g a s h e a t e d t o g e t h e r w i t h a s u b s t r a t e w h i c h i s s e t i n t h e p l a s m a g a s . High d a r k c o n d u c t i v e a n d p h o t o c o n d u c t i v e f i l m s a r e o b t a i n e d u n d e r r f power o f a r o u n d 5 W and g a s t e m p e r a t u r e o f 300°C. T h i s s a m p l e i s f o u n d t o b e p o l y c r y s - t a l l i n e from RHEED. Under h i g h r f power a n d h i g h g a s t e m p e r a t u r e . ( a r o u n d 600°C), a g r o w t h o f a-Si f i l m s w i t h l e s s h y d r o g e n a n d d e f e c t d e n s i t y i s s u g g e s t e d .

I n t r o d u c t i o n . - R e c e n t l y , t h e p r e p a r a t i o n of S i m a t e r i a l s w i t h a m i c r o c r y s t a l l i n e

- -

s t r u c t u r e by g l o w d i s c h a r g e t e c h n i q u e h a s r e c e i v e d a c o n s i d e r a b l e a t t e n t i o n 11-51. I n t h i s c a s e , t h e d e p o s i t i o n c o n d i t i o n w i t h h i g h d e p o s i t i o n t e m p e r a t u r e a b o v e 400°C [ I ] , l o w g r o w t h r a t e b e l o w 0 . 5 A / s [ 2 ] o r h i g h r f power a b o v e 20W [3-51 i s r e q u i r e d . Glow d i s c h a r g e (GD) S i f i l m s , u s u a l l y , a r e d e p o s i t e d o n a h e a t e d s u b s t r a t e by GD o f un- h e a t e d SiH4. We p r o d u c e d undoped G D S i f i l m s by t h e new GD s y s t e m ; SiH& h e a t e d t o - g e t h e r w i t h a s u b s t r a t e i s decomposed by GD, and t h e s u b s t r a t e i s s e t i n t h e p l a s m a g a s . I n t h e p r e s e n t p a p e r , t h e d a r k c o n d u c t i v i t y , p h o t o c o n d u c t i v i t y , ESR, I R a n d o p t i c a l a b s o r p t i o n a r e m e a s u r e d f o r s a m p l e s p r o d u c e d by c h a n g i n g r f power u p t o lOOW and g a s t e m p e r a t u r e u p t o 600°C, and t h e r e l a t i o n s h i p s b e t w e e n t h e s e p r o p e r t i e s a n d morphology a r e d i s c u s s e d .

F x p e r i m e n t a 1 . - The g l o w d i s c h a r g e d e c o m p o s i t i o n s y s t e m employed i n t h e p r e s e n t work

-

was a n i n d u c t i v e l y c o u p l e d r f GD a p p a r a t u s . The s y s t e m i s s c h e m a t i c a l l y shown i n f i g - u r e 1. The r e a c t i o n chamber was q u a r t z t u b e o f 5 0 m i n d i a m e t e r and i n s e r t e d i n a

HEATER COIL h o r i z o n t a l f u r n a c e . A s u b s t r a t e was s e t . i n a h e a t e d p l a s m a g a s . The g a s (20%SiH4+80%H2)

RF COIL- ⁰ b 0' b' was i n t r o d u c e d a t a f l o w r a t e o f 4 . 1 SCCM and

y~g5J

t h e dynamic p r e s s u r e was a b o u t 0 . 2 T o r r . The s a m p l e s w e r e d e p o s i t e d a t t h e same t i m e o n q u a r t z ( f o r ESR and o p t i c a l a b s o r p t i o n mea- s u r e m e n t s ) , g l a s s ( f o r e l e c t r i c a l m e a s u r e - m e n t s ) and s i n g l e c r y s t a l l i n e S i ( f o r IR a b s o r p t i o n m e a s u r e m e n t ) a t g a s t e m p e r a t u r e Tg from 200 t o 600°C. The d e p o s i t i o n r a t e was 1 0 C % 1 5 0 ~ / m i n d e p e n d e n t o n r f power. I l l u m i n a - Fig.l: S c h e m a t i c o f g l o w d i s c h a r g e t i o n i n p h o t o c o n d u c t i v i t y m e a s u r e m e n t s i s

d e c o m p o s i t i o n s y s t e m . MFC r e p r e s e n t s p e r f o r m e d a t p h o t o n i n t e n s i t y o f 4 . 5 ~ 1 0 ~ ~ mass f l o w c o n t r o l l e r . p h o t o n s / c m 2 s by He-Ne l a s e r .

R e s u l t s . - F i g u r e 2 shows t h e d e p e n d e n c e s o f p h o t o c o n d u c t i v i t y a d o n Tg ( = d e p o s i t i o n t e m p e r a t u r e ) f o r s a m p l e s d e p o s i t e d a t v a r i o u s r f power. F o r t h e s a m p l e d e p o s i t e d a t 1.5W, t h e b e h a v i o r s of u p a n d a d are f o u n d t o b e s i m i l a r t o t h o s e f o r GD a - S i produced by o r d i n a r y m e t h o d s [ 1 , 6 , 7 1 . Under r f power o f 5W, u p and a d s h a r p l y i n c r e a s e w i t h i n c r e a s i n g t e m p e r a t u r e up t o 300°C, and t h e n d e c r e a s e . S i m i l a r b e h a v i o r i s a l s o s e e n f o r t h e s a m p l e d e p o s i t e d a t 10W. The d e t a i l e d d e p e n d e n c e s o f a a n d a d o n r f power f o r t h e s a m p l e d e p o s i t e d a t 300°C a r e shown i n f i g u r e 3 t o g e t g e r w i t h t h o s e f o r t h e s a m p l e d e p o s i t e d a t 600°C. A s s e e n i n t h i s f i g u r e , r f power o f a r o u n d 5 W a p p e a r s

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19814149

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C4-676 JOURNAL DE PHYSIQUE

F s : D e p e n d e n c e s o f o p and od o n g a s

w :

D e p e n d e n c e s of o p a n d a d o n r f t e m p e r a t u r e f o r GD S i f i l m s d e p o s i t e d a t power f o r G D S i f i l m s d e p o s i t e d a t g a s r f power o f 1 . 5 , 5 and 101J. The m e a s u r e - t e m p e r a t u r e Tg o f 300 a n d 600°C. The m e n t s a r e c a r r i e d o u t a t room t e m p e r a t u r e . m e a s u r e m e n t s a r e c a r r i e d o u t a t room

t e m p e r a t u r e .

t o b e e s p e c i a l d e p o s i t i o n c o n d i t i o n f o r d e p o s i t i o n a t 300°C. I n o r d e r t o c h e c k u p o n t h e m o r p h o l o g y , RHEED w a s p e r f o r m d on s a m p l e s w i t h a s i m i l a r e l e c t r i c a l p r o p e r t i e s t o t h e s a m p l e s d e p o s i t e d u n d e r c o n d i t i o n s o f 1.5W-30O0C, 514-300°C and 100W-600°C. As t h e r e s u l t , The s a m p l e 5W-300°C was f o u n d t o b e p o l y c r y s t a l l i n e . By means o f t h e p r e s e n t d e p o s i t i o n s y s t e m , t h u s GD S i m a t e r i a l s w i t h a n i c r o c r y s t a l l i n e s t r u c t u r e c a n b e p r o - duced u n d e r low rf power and t e m p e r a t u r e i n c o n t r a s t w i t h o r d i n a r y s y s t e m ( s e e I n t r o - d u c t i o n ) . The o t h e r s a m p l e s showed a d i f f u s e p a t t e r n . F o r t h e s a m p l e s d e p o s i t e d a t 600°C, od i s 1 0 - ~ % 1 0 - ~ / ~ c m and i n d e p e n d e n t of r f power u p t o 100W, b u t o p i n c r e a s e s by 3 G o r d e r s o f m a g n i t u d e .

I n t h e s e s a m p l e s , ESR s i g n a l s w i t h g = 2 . 0 0 5 5 d u e t o d a n g l i n g b o n d s a r e o b s e r v e d . F i g u r e 4 shows t h e d e p e n d e n c e o f t h e s p i n d e n s i t y Ns on r f power. T h e v a l u e s o f Ns f o r t h e s a m p l e s d e p o s i t e d a t Tg b e l o w 500°C i n c r e a s e w i t h i n c r e a s i n g r f power i n a g r e e m e n t w i t h t h a t o f GD a - S i by a n o r d i n a r y method [ 8 ] , b u t Ns f o r t h e s a m p l e de- p o s i t e d a t 600°C d e c r e a s e s w i t h r f power u p t o 50W. A r o u g h c o r r e l a t i o n b e t w e e n Ns

and up c a n b e s e e n from f i g u r e s 2. 3 a n d 4 . However we c a n n o t f i n d a s i g n i f i c a n t i n d i c a t i o n c o r r e s p o n d -

i n g w i t h t h e e s p e c i a l b e h a v i o r o f o p a n d od s e e n i n t h e s a m p l e 51.1-300°C.

The p e a k t o p e a k l i n e w i d t h s f o r t h e s a m p l e s d e - p o s i t e d a t Tg b e l o w 400°C a n d a b o v e 500°C i n c r e a s e a n d d e c r e a s e w i t h t h e i n c r e a s e of Ns, r e s p e c t i v e l y . T h i s r e s u l t s u g g e s t s t h a t t h e l i n e w i d t h f o r t h e f o r m e r is d u e t o a d i p o l e - d i p o l e i n t e r a c t i o n a n d t h a t f o r t h e l a t t e r w i t h h i g h Ns i s n a r r o w e d b y a n e x c h a n g e i n t e r a c t i o n .

w:

Dependence o f s p i n d e n s i t y f o r t h e ESR s i g n a l w i t h g = 2 . 0 0 5 5 o n r f power f o r GD S i f i l m s d e p o s i t e d lds

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⁵ ^;o ^;o ⁵⁰ a t g a s t e m p e r a t u r e b e t w e e n 200 and 600°C. The mea- RF POWER ( W ) s u r e m e n t s a r e c a r r i e d o u t a t room t e m p e r a t u r e .

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Fig.5: Dependence of hydrogen c o n c e n t r a - &6: Dependence o f o p t i c a l gap t i o n e s t i m a t e d from t h e IR a b s o r p t i o n a t c a l c u l a t e d from

&

v s l i w on r f power 2000 and 2090 cm-1 on g a s t e m p e r a t u r e f o r f o r GD S i f i l m s d e p o s i t e d a t g a s tem- GD S i f i l m s d e p o s i t e d a t r f power of 1 . 5 , p e r a t u r e of 200, 300 and 400°C.

5 , 1 0 and 20W.

F i g u r e 5 shows t h e dependence o f hydrogen c o n c e n t r a t i o n NH e s t i m a t e d from I R a b s o r p t i o n a t 2000 cm-l(due t o SiH) and 2090 cm-l(due t o SiH2) on T

.

A s r e v e a l e d from f i g u r e s 4 and 5 , a c l e a r c o r r e l a t i o n between NH (SiH component? and Ns i s f o u n d . T h i s r e s u l t i s c o n s i s t e n t w i t h t h a t of GD a - S i by K n i g h t s e t aZ. [ 8 ] . Here t h e c o r r e - l a t i o n i s between t h e d e c r e a s e o f t h e SiH component and t h e i n c r e a s e of Ns. A c o r r e - l a t i o n between NH ( S i n component) and up i s n o t c l e a r a s shown i n f i g u r e s 2 and 5 , b u t N H 1 s (SiH2 component) f o r t h e s a m p l e s d e p o s i t e d a t 1 . 5 o r 5W a p p e a r t o b e r e l a t e d t o UP. T h i s r e s u l t s u g g e s t s t h e e x i s t e n c e of t h e r e l a t i o n s h i p between SiH2 bonds and c r y s t a l l i z a t i o n . F o r t h e sample d e p o s i t e d a t 600°C, IR a b s o r p t i o n c o u l d n o t be ob- s e r v e d (H c o n c e n t r a t i o n i s s m a l l e r t h a n 1 a t . % ) .

F i g u r e 6 shows t h e dependence of t h e o p t i c a l g a p Ego on r f power. Ego f o r t h e sample d e p o s i t e d a t 300°C monotonously d e c r e a s e s w i t h i n c r e a s i n g r f power, and t h e v a r i a t i o n is below 0.2eV. I n o r d e r t o i n v e s t i g a t e t h e r e l a t i o n s h i p between Ego and a d , t h e a c t i v a t i o n e n e r g y Eu was o b t a i n e d from a r e c i p r o c a l t e m p e r a t u r e p l o t of a d a t around room t e m p e r a t u r e . Ea and t h e p r e - e x p o n e n t i a l f a c t o r a, f o r t h e s a m p l e s 1.5W-300°C and 2W-300°C w e r e 0.81.0.9eV and l%5x104/Qcm, r e s p e c t i v e l y , w h i l e t h o s e f o r t h e s a m p l e s 5W-300°C and 10W-300°C were 0 . 4 5 ~ 0 . 5 5 e V and 0 . 5 % 1 x 1 0 ~ / Q c m , r e s p e c t i v e l y . Thus Ea f o r t h e f o r m e r is a b o u t 1 1 2 of Ego, and Ea f o r t h e l a t t e r is c o n s i d e r a b l y s m a l l e r t h a n EW/2 and n e a r w i t h t h a t f o r a n i n t r i n s i c s i n g l e c r y s t a l l i n e S i . The v a l u e of a. i s n e a r l y c o n s t a n t i n d e p e n d e n t o f a d . The a c t i v a t i o n e n e r g y E s o b t a i n e d from t h e r m o e l e c t r i c power f o r a sample w i t h a s i m i l a r e l e c t r i c p r o p e r t y t o t h e l a t t e r sample was 0.55eV i n agreement w i t h Ea.

D i s c u s s i o n a n d summary.- I t is c l e a r from t h e p r e c e e d i n g s e c t i o n s t h a t a c l e a r c o r - r e l a t i o n d o e s n o t e x i s t between e l e c t r i c a l p r o p e r t i e s and d e f e c t d e n s i t y , Si-H v i b r a - t i o n a l s p e c t r a o r o p t i c a l g a p f o r t h e s a m p l e s d e p o s i t e d a t below 500°C e x c e p t f o r t h a t between u p and NH (SiH2 component) f o r t h e sample d e p o s i t e d a t 1 . 5 o r 5CJ. One o f t h e o r i g i n s a p p e a r s t o b e t h e e f f e c t of c r y s t a l l i z a t i o n . The sample 5W-300°C w i t h h i g h up and ad h a s a m i c r o c r y s t a l l i n e s t r u c t u r e , and t h e v a l u e s of Ea (=Es) and a 0 i s n e a r w i t h t h o s e f o r a n i n t r i n s i c s i n g l e c r y s t a l l i n e S i , though t h e Ego i s l a r g e . From t h i s r e s u l t s , i t i s i n f e r r e d t h a t t h e e l e c t r i c a l t r a n s p o r t i n t h e sample m a i n l y p a s s e s t h r o u g h a c r y s t a l l i n e p h a s e p o r t i o n . SiH2 b o n d s ' a r e l i k e l y t o exist s u r r o u n d - i n g t h e c r y s t a l l i n e p h a s e p o r t i o n , b e c a u s e NH (SiH2 component) a p p e a r s t o i n c r e a s e w i t h c r y s t a l l i z a t i o n a s shown i n f i g u r e 5 . Supposing t h e d a n g l i n g bonds e x i s t i n amorphous p h a s e p o r t i o n , no c o n n e c t i o n between e l e c t r i c a l p r o p e r t i e s and N s c a n b e e x p l a i n e d .

F o r t h e sample d e p o s i t e d a t 600°C, Ns and u p , r e s p e c t i v e l y , d e c r e a s e s and i n - c r e a s e s w i t h i n c r a s i n g r f power i n c o n t r a s t w i t h t h a t a t Tg below 500°C. From RHEED a n a l y s i s , t h e s e s a m p l e s , even t h a t d e p o s i t e d a t 100W, showed a t y p i c a l amorphous p a t t e r n . Under s u c h h i g h Tg and h i g h r f power c o n d i t i o n , i t i s e x p e c t e d t h a t SiH4 i s

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C4-678 JOURNAL DE PHYSIQUE

c o m p l e t e l y decomposed a n d b a r e S i a t o m s d e p o s i t e d o n s u r f a c e o f a - S i a r e t h e r m a l l y r e l a x e d i n Lhe s u r f a c e l a y e r . I n t h i s c o n d i t i o n , a g r o w t h o f a n i d e a l a - S i f i l m s w i t h l e s s h y d r o g e n a n d d e f e c t d e n s i t y i s e x p e c t e d . U n d e r l o w r f power a n d h i g h Tg, i t i s e x p e c t e d t h a L H a t o m s a r e i n c o r p o r a t e d i n s i d e o f t h e m a t e r i a l b e c a u s e o f i n c o m p l e t e - n e s s o f d e c o m p o s i t i o n o f SiH4 a n d t h e n t h e r m a l l y e f f u s e d . I n s u c h a c a s e , h i g h d e n s i t y o f d e f e c t s s h o u l d b e g e n e r a t e d b e c a u s e movement o f S i a t o m s i n b u l k i s h a r d . Acknowledgemeii~_s.- T h c a u t h o r s w o u l d l i k e t o e x p r e s s t h e i r s i n c e r e t h a n k s t o P r o f . --

T . S h i m i z u f o r s t i m u l a t i n g d i s c u s s i o n s a n d D r . S . Yamaznki o f S e m i c o n d u c t o r E n e r g y L a b o r a t o r y f o r c a r r y i n g ouL KHEED a n a l y s i s , a n d Mr. S . T a k e n a k a a n d D. Ando f o r e x p e r i m e n t a l a s s i s t a n c e .

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[ 4 ] A. H a t z u d a , S. Y a m a s a k i , K . Nakagawa, H . O k u s h i , K . T a n a k a a n d S . I i z i m a , J a p . J . A p p l . P h y s .

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[ 5 ] Y . M i s h i m a , T . H a m a s a k i , H. K u r a t a , 11. H i r o s e a n d Y . O s a k a , J a p . J . A p p l . P h y s . 2 0 ( 1 9 8 1 ) L121.

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[ 7 ] D. A. A n d e r s o n a n d W . E. S p e a r , P h i l . n a g .

36

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[ 8 ] J . C. K n i g h t s , G . L u c o v s k y a n d R . J . Nemanich, J . N o n - C r y s t a l l i n e S o l i d s 32 ( 1 9 7 9 ) 3 9 3 .