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INTERACTION BETWEEN ARGON AND DOPANTS IN SPUTTERED a-Si : H
M. Toulemonde, J. Grob, J. Bruyère, A. Deneuville, H. Hamdi, P. Siffert
To cite this version:
M. Toulemonde, J. Grob, J. Bruyère, A. Deneuville, H. Hamdi, et al.. INTERACTION BETWEEN ARGON AND DOPANTS IN SPUTTERED a-Si : H. Ninth International Conference on Amorphous and Liquid Semiconductors, 1981, Grenoble, France. pp.C4-799-C4-801, �10.1051/jphyscol:19814175�.
�jpa-00220800�
JOURNAL DE PHYSIQUE
CoZ Zoque C4, suppZQment au nO1O, Tome
4 2 ,octobre 1981 page
C4-799INTERACTION BETWEEN ARGON AND DOPANTS I N SPUTTERED a-Si:H
M. Toulemonde, J . J . Grob, J . C . ~ ~ u ~ ~ r e * , A . ~ e n e u v i l l e * , H. ~ a m d i * and P . S i f f e r t
Centre de Recherches NucZlaires, Groupe
dePhysique e t Applications des Semiconducteurs (PHASE), 67037 Strasbourg Ceder, Prance
* Groupe des Transitions de l'hases,
C . IV'. R. S.,38042 GrenobZe Cedex, France
A b s t r a c t .
-
The c o n c e n t r a t i o n s of A s , B , H , Ar and S i i n s p u t t e r e d a-Si:H a r e measured by helium Rutherford b a c k s c a t t e r i n g and n u c l e a r r e a c t i o n s a n a l y s i s . Excess o r d e f i c i t o f hydrogen and argon by com- p a r i s o n w i t h i n t r i n s i c a-Si:H a r e found i n presence o f dopants a t high d e p o s i t i o n r a t e . T h i s i s r e l a t e d t o t h e plasma d e p o s i t i o n method and would s u g g e s t micro g r a i n s t r u c t u r e i n t h e d e p o s i t e d l a y e r .I n t r o d u c t i o n .
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I n making s p u t t e r e d amorphous s i l i c o n it i s impossible t o avoid t h e presence of argon. I n c o n t r a r y t o hydrogen, t h e r o l e of which i s understood(1, 2 , 3, 4 ) , t h e argon was always c o n s i d e r e d a s i n a c t i v e . I n t h e p r e s e n t work t h e v a r i a t i o n of A r c o n c e n t r a t i o n i n i n t r i n s i c a-Si:H and doped a-Si:H w i l l be determi- ned and t h e p o s s i b l e i n t e r a c t i o n s with o t h e r s p e c i e s of t h e m a t r i x w i l l be d i s c u s s e d i n term of amorphous s t r u c t u r e .
Experimental methods.
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The samples used i n t h i s s t u d y , were prepared a t 190°C by r f c a t h o d i c s p u t t e r i n g of a s i l i c o n t a r g e t w i t h d i f f e r e n t combinations of t h r e e r e - a c t i v e g a s m i x t u r e s a t a t o t a l p r e s s u r e of 9 x 10-3 t o r r . The pourcentage of dibo- r a n e has v a r i e d i n o r d e r t o p r e p a r e d i f f e r e n t samples with d i f f e r e n t c o n c e n t r a t i o n of boron. The s u b s t r a t e t a r g e t h o l d e r were kept a t v a l u e s corresponding t o deposi- t i o n r a t e between 20 i/mn t o 150g/m.
Each sample was d e p o s i t e d on a 100fi
c-Si and t h e i r t h i c k n e s s e s have been measured by i n t e r f e r e n c e f r i n g e s .Ar and S i c o n c e n t r a t i o n was deduced from Rutherford b a c k s c a t t e r i n g mea- surements. Hydrogen was p r o f i l i n g u s i n g t h e 1. ( l s ~ , a ) 12c r e a c t i o n (1,5) and t h e boron p r o f i l i n g and/or c o n c e n t r a t i o n were deduced from "B ( ~ , a ) ~ ~ e r e a c t i o n a t Ep = 163 keV (6,s).
R e s u l t s and d i s c u s s i o n s .
I n t r i n s i c a-Si:H. The r e s u l t s a r e show on f i g . 1 where t h e e v o l u t i o n of A r , H and S i v e r s u s t h e d e p o s i t i o n r a t e a r e r e p o r t e d . These v a l u e s a r e determined by compari- son t o t h e number of atoms i n a c r y s t a l l i n e s i l i c o n . The argon c o n c e n t r a t i o n a t 200 i/m has been determined a t Montreal ( J . C . BruyBre e t a l . p r i v a t e communication) The f i r s t remark i s an i n v e r s e e v o l u t i o n of t h e H and Ar compared t o t h e s i l i c o n , more s i l i c o n i n h i b i t s t h e i n t r o d u c t i o n of argon and hydrogen. The second remark i s t h e two o r d e r of magnitude change i n t h e s p i n d e n s i t y measurement ( 7 ) . Moreover a t high d e p o s i t i o n r a t e a posthydrogenation d i d n o t change t h e number of s p i n . Conse- q u e n t l y it seems t h a t t h e dense m a t r i x d i d not a l l o w t h e d i f f u s i o n of hydrogen t o - wards t h e e x i s t i n g d e f e c t s when a f t e r t h e d e p o s i t i o n . A s i n a glow d i s c h a r g e prepa- r a t i o n even f o r a dense m a t r i x t h e number of s p i n does not kept s o high v a l u e s
( e ) ,
i t appear t h a t t h e i n c l u s i o n of argon i n h i b i t s t h e p o s s i b i l i t y of t h e hydrogen t o s a t u r a t e t h e e x i s t i n g d e f e c t s .Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19814175
C4-800 JOURNAL DE PHYSIQUE
Doped a-Si:H. The f i g . 2 shows t h e e v o l u t i o n of B and 14 a s a f u n c t i o n of t h e i n i t i a l g a s mixture. The do- pant e f f i c i e n c y i s around 55 a t low de- p o s i t i o n r a t e and 12 a t high. A t low boron c o n c e n t r a t i o n , t h e hydrogen c o n c e n t r a t i o n r e a c h t h e one d e t e r m i - ned i n i n t r i n s i c a-Si:H. This i n c o r - p o r a t i o n i s i d e n t i c a l t o t h a t of a r s e n i c
( 1 0 ) . Now c o n c e n t r a t e our purpose on samples p r e p a r e a t h i g h d e p o s i t i o n r a t e
(130 i/min) and high doping l e v e l . The d i r e c t l i n k between dopants (B,P and A S ) , and hydrogen h a s been shown p r e v i o u s l y ( 9 , 1 0 , l l )
.
Moreoveron t h e following t a b l e we can s e e t h a t t h e argon c o n c e n t r a t i o n i s low i n able 1 : mean c o n c e n t r a t i o n (%)
dopants H Ar
n l a y e r (As) 5 13 1
p l a y e r (B) 5 4 7
t h e n l a y e r compare t o i n t r i n s i c a-Si:H and high i n t h e p l a y e r . A s , when dopants a r e implant i n amorphous a-Si:H t h e hydrogen c o n c e n t r a t i o n i s not i n f l u e n c e d i n t h e same manner
(F.J. Demond e t a l . p r i v a t e communi- c a t i o n ) t h e v a r i a t i o n of hydrogen and argon should f o l l o w t h e amorphous n u c l e a t i o n d u r i n g t h e d e p o s i t i o n . One p o s s i b l e e x p l a n a t i o n would s u g g e s t t h a t t h e n u c l e a t i o n proceeds by microscopic amorphous g r a i n ( 4 )
,
t h e dopants s t a n d i n g mainly a t t h e s u r f a c e of t h e g r a i n . Indeed t h i s c o u l d e x p l a i n t h a t a t g r a i n boundaries it i s p o s s i b l e t o add argon atom when t h e r e i s no hydrogen a s it i s t h e c a s e w i t h boron and t h e c o n t r a r y w i t h a r s e n i c . A st h e r e i s l e s s hydrogen with boron dopant, t h i s would s u g g e s t t h a t boron a c t a s d e f e c t s p a s s i v a t i o n . These d e f e c t s could be i n t h e volume of t h e arnor- phous g r a i n and n o t a t t h e s u r f a c e , but it would be t h e n d i f f i c u l t t o add more a r g o n , except a t t h e g r a i n boundary s i n c e hydrogen l i n k e d t o t h e s i l i c o n would s t a n d h e r e .
Pig. 1 : H , S i , Ar concentra- t i o n ($1 and s p i n d e n s i t y
(cm-3)
Fig. 2 : B and hydrogen i n c o r - p o r a t l o n a s f u n c t i o n of g a s mixture f o r h i g h and low d e p o s i t i o n r a t e
R e f e r e n c e s
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