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THE CO2 LASER OPTOACOUSTIC SPECTRA OF SILICANE, PHOSPHINE AND BORANE
C. Ming, I. Liu, C. Chen
To cite this version:
C. Ming, I. Liu, C. Chen. THE CO2 LASER OPTOACOUSTIC SPECTRA OF SILICANE, PHOSPHINE AND BORANE. Journal de Physique Colloques, 1983, 44 (C6), pp.C6-533-C6-536.
�10.1051/jphyscol:1983687�. �jpa-00223246�
JOURNAL DE PHYSIQUE
Colloque C6, suppl6ment au nO1O, Tome 44, octobre 1983 page C6- 533
T H E C02 LASER OPTOACOUSTIC SPECTRA OF SILICANE, PHOSPHIME AND BORANE
C. Ming, I. Liu and C. Chen
Changchun Institute of Applied Chemistry, Academia Sinica, China
R6sum6
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On d 6 c r i t un montage, pour d s t e c t e r avec un l a s e rZi C02 p a r s p e c t r o s c o p i e o p t o a c o u s t i q u e d e s gaz t e l s que l e s i l a n e , l e borane e t l e phosphine. Le f a i t que l e u r s p e c t r e PA s o i t d i f f 6 r e n t rend p o s s i b l e l ' u t i l i s a t i o n d ' u n l a s e r TEA C02 pour l a p u r i f i c a t i o n du s i l a n e
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Equipment and method f o r d e t e c t i n g s i l i c a n e , ph- o s p h i n e and borane by C02 l a s e r o p t o a c o u s t i c spectro--scopy have been d e s c r i b e d . E x p e r i m e n t a l r e s u l t s show t h a t t h e c h a r a c t e r i s t i c absorp- t i o n of s i l i c a n e , phosphine and borane d i f f e r s from e a c h o t h e r , w h i c h makes p o s s i b l e t h e u s e of TEA C02 l a s e r i n t h e p u r i f i c a t i o n ofs i l i c a n e .
Along w i t h t h e wider a p p l i c a t i o n of l a s e r t e c h n i q u e s , much a t t e n t i o n h a s a l s o been p a i d on c e r t a i n fundamental r e s e a r c h work which a r e c l o s e l y r e l a t e d t o p r o d u c t i o n p r a c t i c e , s u c h a s t h e p u r i f i c a t i o n of s i l i c a n e .
S i l i c a n e i s a raw m a t e r i a l w i d e l y u s e d i n t h e i n d u s t r y of i n t e g r a t e d c i r c u i t s and o t h e r semiconductor d e v i c e s f o r d o p o s i t i n g p o l y c r y s t a - l l i n e f i l m s of s i l i c o n , s i l i c o n n i t r i d e and s i l i c o n oxide. The q u a l i - t y of t h e p o l y c r y s t a l l i n e s i l i c o n f i l m s depends t o a g r e a t e x t e n t on t h e p u r i t y of t h e raw s i l i c a n e g a s which u s u a l l y c o n t a i n s some v o l a - t i l e compounds of
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a n d y f a m i l y e l e m e n t s ( b o r a n e , phosphine and a r s h i n e ) . While c o n v e n t i o n a l p u r i f i c a t i o n methods work w i t h low e f f i - c i e n c y , t h e l a s e r p u r i f i c a t i o n method f e a t u r e s t h a t it i s p o s s i b l e t o u s e s u i t a b l e l a s e r beams which a c t o n l y w i t h t h e i m p u r i t i e s and t h u s e f f e c t t h e p u r i f i c a t i o n of s i l i c a n e w i t h r e l a t i v e l y h i g h s e l e c - t i v i t y .C l a r k and d a r t f o r d / I - 3 / have r e p o r t e d t h e u s e of u l t r a v i o l e t ArF l a s e r f o r p u r i f y i n g s i l i c a n e . Freund e t a l . u s e d a TEA CG l a s e r f o r c a r r y i n g o u t t h e d i s s o c i a t i o n of borane. Cunninghan /4/ A d o t h e r s p o i n t e d o u t t h a t C02 l a s e r can a l s o be u s e d f o r s i l i c a n e p u r i f a c a t i o - n.
I n t h e p r e s e n t work, w i t h a self-made C O l a s e r o p t o a c o u s t i c s p e c t r o - m e t e r
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we measured t h e a b s o r p t i o n s p e ' & t r a of s i l i c a n e and i t s i m - p u r i t i e s ( p h o s p h i n e and b o r o n e ) w i t h i n t h e spectrum r a n g e of C Gl a s e r i n o r d e r t o e x p l o r e t h e way of p u r i f y i n g s i l i c a n e by s e l g c t i v e e x c i t a t i o n a c c o r d i n g t o t h e c h a r a c t e r i s t i c a d s o r p t i o n l i n e s of t h e s e compounds. Experiments showed t h a t t h e c h a r a c t e r i s t i c a b s o r p t i o n of d i f f e r s c o n s i d e r a b l y w i t h t h o s e of phosphine and b o r a n e , t h e r e f o r e t h e p o s i b i l i t y of p u r i f y i n g s i l i c a n e w i t h a C02 l a s e r was confirmed.
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E x p e r i m e n t a l S e t u pThe o p t o a c o u s t i c t e c h n i q u e s i s b a s e d on t h e o p t o a c o u s t i c e f f e c t of g a s e s . Fig. 1 shows o u r e x p e r i m e n t a l s e t u p . The o p r a t i o n of t h i s s y s - tem h a s been d e s c r i b e d i n r e f e r e n c e
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I n o r d e r t o i n c r e a s e t h el a s e r t r a n s m i s s i v i t y , o p t o a c o u s t i c c e l l s w i t h Brewster t y p e window
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1983687
C6-534 JOURNAL DE PHYSIQUE
were u s e d t o match w i t h t h e 3 r e w s t e r window of t h e C:$ l a s e r . The s t r u c t u r e of t h e o p t o a c o u s t i c c e l l i s s7?.own i n F i g . 2. X.21 c r y s t a l w i t h s u i t a b l e a b s o r p t i o n c o e f f i c i e n t /6/ was u s e d a s window p l a t e w h i l e h i g h - s e n s i t i v i t y l o w - n o i s e CXZ t y p e m i c r o p h o n e i o b t a i n e s from l a c t o r y
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S h e n y a n g ) was s e l e c t e d a s a c o u s t i c s e n s o r .2
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Method and T r o c e d u r eD i f f e r e n t i a l method ( w i t h two a b s o r p t i o n c e l l s A and I3 f o r d e d u c t i o n b a c k g r o u n d s i g n a l ) was employed i n d e t e c t i n g s i l i c a n e
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p h o s p h i n e a n d b o r a n e g a s e s . The s a m p l e g a s e s were o b t a i - n e d from n e m i c o n d u c t o r N a t e r i a l F a c t o r y of 3 a o d i n g C i t y . The c o n c e n t r a t i o n s of s i l i c a n e , p h o s p h i n e and b o r a n e were d i l u t e d t o 2-59', 1"' and I F ' r e s p e c t i v e l y w i t h !Ir g a s . The p u r i t y of t h e Ar g a s u.sed was h i g h e r t h a n 519.99'.A s t h e g a s s a m p l e s t o be d e t e c t e d were t o x i c and c o m b u s t i b l e i n a i r , e x p e r i m e n t s were c a r r i e d o u t i n c l o s e d o p t o a c o u s t i c c e l l s . . ? r i o r t o e x p e r i m e n t s , l e t n i t r o g e n g a s p a s s t h r o u - g h t h e c e l l s t o e x c l u d e t h e a i r , m e a n s h i l e t u r n on t h e l a s e r . A f t e r a s t a b i l i z i n g p e r i o d of 20 m i n u t e s , s t o p n i t r o g e n p u r g i n g a n d b e g i n measurement. F i r s t measure t h e background s i g n a l w i t h o u t sample g a s i n c e l l A , i . e . w i t h b o t h c e l l s B and 3 s t i l l f i l l e d w i t h n i t r o g e n . T h i s i s done u n d e r c o n d i - t i o n s o f complete c o m p e n s a t i o n w h i c h i s a c c o m p l i s h e d by p r e c i s e l y a d j u s t i n g t h e a t t e n u a t o r of c e l l B( t h e r e f e r e n c e c e 1 . l ) u n t i l t h e s i - g n a l s of b o t h c e l l s a r e e x a c t l y e q u a l , t h a t i s a t B-3=0. Then i n t r o - d u c e s a m p l e g a s i n t o c e l l .A, a p p l y b o t h s i g n a l s A and 3 t o t h e l o c k - i n a m p l i f i e r a n d p e r f o r m t h e d i f f e r e n t i a l a m p l i c a t i o n a n d measurment of .h-8. The o u t p u t of t h e l o c k - i n a m p l i f i e r , r e c o r d e d on a
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r e c o r - d e r , r e p r e s e n t s t h e u n n o r r n a l i z e d o p t o a c o u s t i c s p e c t r a of t h e sampl-es a s shown i n 2 i g . 3 . 1111 e x p e r i m e n t s i n t h i s work were p e r f o r m e d t w i c e . It i s n e c e s s a r y t o p u r g e t h e o p t o a c o u s t i c c e l l w i t h n i t r o g e n g a s a n d measure t h e b a c k g r o u n d a f t e r e a c h measurement.The o p t o a c o u s t i c s p e c t r a of g a s e s s i l . i c a n e , n h o s p h i n e and b o r a n e w i t h i n t h e s p e c t r u m r a n g e of C\: l a s e r a r e shown i n F i g . 3. It c a n be s e e n t h a t w h i l e t h e main a b s g r p t i o n o f s i l i c a n e l i e s a t b r a n c h 10 Y j , t h e main a b s o r p t i o n o f p h o s p h i n e l i e s a t b r a n c h e s 9 ? and
9
R , a n d t h e s t r o n g a b s o r p t i o n o f b o r a n e l i e s a t b r a n c h 1 0R.
As t h e c h a r a c t e r i s t i c a b s o r p t i o n s of s i l i c a n e a n d i t s i m p u r i t i e s p h o s p h i n e and b o r a n e d i f f e r c o n s i d e r a b l y w i t h i n t h e s p e c t r u m r a n g e of C L 2 l a s e r , we c a n c h o o s e d i f f e r e n t b r a n c h e s of t h e CC l a s e r t o e x c i t e p h o s p h i n e a n d b o r a n e f o r t h e p u r i f i c a t i o n of s i l i s a n e . :'or e x a m p l e , i r r a d i a t i o n w i t h e i t h e r b r a n c h 10R ( t h e c h a r a c t e r i s t i c a b s o r p t i o n r e g i o n o f b o r a n e ) o r b r a n c h
9P
! t h e c h a r a c t e r i s t i c a b s o r - u k i o n r e g i o n o f p h o s p h i n e ) :?:ill c b u s e p h o s p h i n e and b o r a n e t o d i s s - o c i a t e and l e a v e s i l i c a n e p u r i f i e d . So f a r t h e r e l e v a n t s p e c t r u m d a t a r e p o r t e d i n l i t e r a t u r e w i t h i n t h e s p e c t r u m r a n g e of C C l a s e r c a n o n l y be f o u n d f o r s i l i c a n e/7/
b u t n o t f o r p h o s p h i n e a n 8 b o r a n e . Our e x p e r i m e n t s shoud be usefu.1 i n p r o v i d i n g some r e f e r e n c e s p e c t r u m d a t a f o r p u r i f y i n g s i l i c a n e w i t h t h e a i d o f a TEi CG2 L a s e r .ricknowledgements. de t h a n k i"r.3au Chunl l n a n d I l s s I l u S h l u y l n g f o r n e l p s I n o u r work. kid we would l l k e t o t h a n k 3 - 0 f . Y 1 T i a n y l n g a d bhang Yousong f o r f r a t e r n a l h e l p s .
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Chen Chuanwen, e t a l . , Chinese physic.^, z ( 1 9 8 2 ) 451.6. Ming Changjiang, e.t a l . , Chinese P h y s i c s , ~ ( 1 9 8 2 ) 453.
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Fig. 1. Block diagram of t h e l a s e r o p t o a c o u s t i c s p e c t r o m e t e r
Fig. 2. C o n s t r u c t i o n of o p t o a c o u s t i c c e l l used i n our work
JOURNAL DE PHYSIQUE
F i g . 3 . The e m i s s i o n power s p e c t r u m o f CJ7 C C l a s e r ( a ) The o p t o a c o u s t i c s p e c t r u m o f BiH4 an8 GO2
l a s e r power s p e c t r u m ( b )
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The o p t o a c o u s t i c s p e c t r u m o f B2Hg and CG2 l a s e r power s p e c t r u m (d)
