NMR AND ESR STUDIES ON ANNEALING EFFECTS IN a-Si : F : H AND a-Si : H

HAL Id: jpa-00220782

https://hal.archives-ouvertes.fr/jpa-00220782

Submitted on 1 Jan 1981

HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

NMR AND ESR STUDIES ON ANNEALING EFFECTS IN a-Si : F : H AND a-Si : H

S. Ueda, M. Kumeda, T. Shimizu

To cite this version:

S. Ueda, M. Kumeda, T. Shimizu. NMR AND ESR STUDIES ON ANNEALING EFFECTS IN a-Si : F : H AND a-Si : H. Journal de Physique Colloques, 1981, 42 (C4), pp.C4-729-C4-732.

�10.1051/jphyscol:19814159�. �jpa-00220782�

JOURNAL DE PHYSIQUE

CoZZoque C4, suppZ6ment au nO1O, Tome 42, octobre 1981 page C4-729

NMR AND ESR STUDIES ON ANNEALING EFFECTS IN a-Si:F:H AND a-Si:H

S. Ueda, ?l. Kumeda and T. Shimizu

DeparLment of EZectronics, Kanazma University, Kanazawa 920, Japan

Abstract.- Measurezents of N1.Z of F in a-Si:F:H and a-Si:F have been carried out and the results are compared with those of H in a-Si:F:H and a-Si:lt.

Effects of motional narrowing on the linewidth of F NIIR in a-Si:F:H show that some fraction of F is incorporated in the form of SiF, or (SiF2)n which tends to move easily. Xhen samples are annealed, the increase in the ESR center density is remarkable in a-Si:F:H and a-Si:H corresponding to the decrease in the H content, but the increase in the ESR center density is rather small in hydrogen free a-Si:F.

Introduction.- Investigations of H and/or F incorporation scheme and their distri- butions in a-Si are inportant in order to know the mechanism of reducing the densi- ty of defects. Nl!R is a very powerful technique for such investigations in con- junction with IR measurements. N t T measurements of H in a-Si:H have already been carried out by several workers, and interesting informations have been obtained(1

-

31. Kere, we kill report for the first tine the results of N1R measurenents of F in a-Si:T:l: and a-Si:F and compare them with the results of H in a-Si:H and a-Si:F:K. In order to study the relation betgeen incorporated H and/or F and de- fects, we have also measured ESR for the same samples. Especially, we have inves- tigated how the results of NI!R and ESP, change with annealing. As a result, we have found interesting difference between the effects of H and F. Ke also found for some cases the narrowinp, of NMP. lines by raising a measurement temperature. To our knowledge this is also the first report of ESR for fluorinated a-Si. A part of the present work was already published[4].

Experimental.- a-Si:H and a-Si:F films uere prepared by rf sputtering and a-Si:F:H films were prepared by dc glow discharge. Preparation conditions are briefly sum- marized in Table 1. All samples were prepared on aluminium foils which were dis- solved off before measurenents. NMR measurenents were performed with a pulse NER

spectrometer at 16 Eniz at 4.2 K, 77 K and room temperature. The free induction decay (FID) following a 90° pulse were averaged by computer accumulation and Fourier-transformed. ESR measurements were performed with a JEOL PE 3X spectrome- ter at room temperature. MIR and ESR measurements were made for the same sample after each step of isochronal annealing for 1 h in a vacuum of < Torr.

Table I. sample preparation COndltlOnS

Results.- The NPIR spectra of H in either a-Si:H or a-Si:F:H at 77 K can be decom- posed into a broad Gaussian line and a narrow Lorentzian line in agreement with the

a-Si:F:H

dc glow discharge SiF4

+

H2

1.0 Torr 12.5 % H2 300°C a-Si:F

rf sputtering Ar

+

SiF4 0.04 Torr 6 % SiF, 350°C Preparation method

Gas

Gas pressure Gas fraction

Substrate temperature

a-Si:H

rf sputtering Ar

+

^H2

0.11 Torr 40 % H2 water cooled

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19814159

C4-730 JOURNAL DE PHYSIQUE

p r e v i o u s w o r k s [ l , 21. The NMR s p e c t r a o f F a t 77 K i n a - S i : F a r e a l s o composed o f t h e two c o m p o n e n t s , b u t t h o s e i n a-Si:F:H h a v e n o n a r r o w component ( l e s s t h a n s e v - e r a l % o f t h e b r o a d component i n t h e i n t e n s i t y r a t i o ) . The c o n t e n t s o f H and F c o n t r i b u t i n g t o t h e component l i n e s a r e shown i n T a b l e 2 t o g e t h e r w i t h t h e NH'R l i n e w i d t h s .

C h a n g e s w i t h a n n e a l i n g o f H c o n t e n t s o b t a i n e d from NMR a t 77 K a r e shown i n F i g . 1. The H c o n t e n t c o n t r i b u t i n g t o t h e b r o a d l i n e d e c r e a s e s w i t h a n n e a l i n g t e m p e r a t u r e f a s t e r t h a n t h a t c o n t r i b u t i n g t o t h e n a r r o w l i n e . Changes w i t h a n n e a l - i n g o f F c o n t e n t s o b t a i n e d from NMR a t 77 K a r e shown i n F i g . 2. A n a r r o w l i n e a p p e a r s a n d i n c r e a s e s i n F s p e c t r a o f a-Si:F:H by a n n e a l i n g a b o v e 450°C, b u t t h e t o t a l F c o n t e n t d o e s n o t c h a n g e w i t h a n n e a l i n g . The F NMR s p e c t r a i n a - S i : F d o e s n o t a p p r e c i a b l y c h a n g e w i t h a n n e a l i n g . F i g u r e 3 shows t h e t e m p e r a t u r e d e p e n d e n c e o f XMR l i n e w i d t h s .

Changes w i t h a n n e a l i n g o f t h e c e n t e r d e n s i t i e s o f t h e ESR s i g n a l d u e t o d a n g l - i n g b o n d s a r e shown i n F i g . 4 . I n a-Si:H a n d a-Si:F:H, t h e ESR c e n t e r d e n s i t y i n - c r e a s e s by two o r d e r s of m a g n i t u d e by a n n e a l i n g . I n a - S i : F , however, t h e i n c r e a s e i s n o t s o p r o m i n e n t .

T a b l e 2. 11 a n d F c o n t e n t s c o n t r i b u t i n g t o t h e b r o a d and n a r r o w Nt!R l i n e s a t 77 K i n a s - d e p o s i t e d f i l m s . F u l l w i d t h h a l f maximum (FIJHEI) o f t h e s e l i n e s a r e shown i n p a r e n t h e s e s .

D i s c u s s i o n . - The o r i g i n o f t h e b r o a d and n a r r o w l i n e s o f H NNR s p e c t r a i n a-Si:H h a s b e e n d i s c u s s e d by s e v e r a l a u t h o r s , a n d t h e n a r r o w l i n e i s c o n s i d e r e d t o o r i g i - n a t e from H d i s p e r s e d i n t h e form o f s i l i c o n m o n o h y d r i d e (SiH) and t h e b r o a d l i n e from c l o s e l y g a t h e r e d H [ 3 , 5, 61. The c o n s i d e r a t i o n i s b a s e d on t h e f a c t t h a t m o t i o n a l n a r r o w i n g is n o t a m a j o r f a c t o r i n t h e l i n e w i d t h d e t e r m i n a t i o n and temper- a t u r e i n d e p e n d e n t l i n e w i d t h i s d o m i n a t e d by d i p o l a r i n t e r a c t i o n .

annealing temperature ^{( O C} ) annealing temperature ^{( O C )} F c o n t e n t ( a t . % ) b r o a d (>WH:.kIiz) narrow(FWHK,kHz) - -

1 3 . 6 ( 2 3 . 2 ) -

1 2 . 4 ( 2 2 . 0 ) 4 . 4 ( 8 . 0 ) a-Si:H

a-Si:F:H a - S i : F

F i g . 1. Changes w i t h a n n e a l i n g o f H F i g . 2. Changes w i t h a n n e a l i n g of F c o n t e n t s i n a-Si:H and a-Si:F:H ob- c o n t e n t s i n a - S i : F and a-Si:F:H ob- t a i n e d from KMR a t 77 K. t a i n e d from NFR a t 7 7 K .

H c o n t e n t ( a t . %)

b r o a d (FWHE1,kHz) narrow(Fk'til.'.kHz) 2 0 . 9 ( 2 4 . 0 ) 1.1 ( 3 . 5 ) 1 2 . 2 ( 2 3 . 4 ) 2.4 ( 5 . 3 )

- -

I n t h e p r e s e n t c a s e , however, t h e l i n e w i d t h s o f H a n d F P E R w e r e f o u n d t o c h a n g e i n some c a s e s w i t h t e m p e r a t u r e a s shown i n F i g . 3 . E s p e c i a l l y , F NMR s p e c t r a i n a-Si:F:H a n n e a l e d a t 600°C e x h i b i t t h e p r o m i n e n t t e m p e r a t u r e d e p e n d e n c e : The s p e c t r u m a t 4.2 K i s a s i n g l e b r o a d l i n e , t h a t a t 77 K is a s u p e r p o s i t i o n o f a b r o a d a n d a n a r r o w l i n e s and t h a t a t room t e m p e r a t u r e is a s i n g l e n a r r o w l i n e . Hence, t h e n a r r o w l i n e i n t h i s c a s e s h o u l d b e m o t i o n a l n a r r o w e d o n e , and i s c o n s i d - e r e d t o o r i g i n a t e from F which i s e a s y L O move and n o t f r o m d i s p e r s e d F. F WIR s p e c t r u m i n a s - d e p o s i t e d a-Si:F:H a l s o e x h i b i t s t h e e f f e c t o f m o t i o n a l n a r r o w i n g a l t h o u g h t h e e f f e c t i s n o t s o p r o m i n e n t . T h e s e f a c t s s u g g e s t t h a t F i n a - S i : F : l i t a k e s m o v a b l e f o r m s w i t h d i f f e r e n t d e g r e e s of f e a s ' b i l i t y f o r movement. The i n f r a - r e d a b s o r p t i o n peak a t 1 0 1 0 cm-' i n f l u o r i n a t e d a - S i i s a t t r i b u t e d t o S i F 4 [ 7 ] o r ( S i F 2 2 , La] g r o u p s . T h e s e g r o u p s may b e e a s y t o m o v e t o c a u s e t h e m o t i o n a l n a r r o w i n g . S i n c e t h e a n n e a l i n g i s known t o i n c r e a s e t h e i n f r a r e d a b s o r p t i o n p e a k a t 1 0 1 0 cm-' f o r a - S i : F : l i [ 7 ] , i t i s r e a s o n a b l e t h a t t h e n a r r o w i n g e f f e c t i s more p r o m i n e n t i n t h e a n n e a l e d f i l m s . The l i n e w i d t h s o f F

m 3

a t 4 . 2 K , which w i l l b e f r e e from no- t i o n a l n a r r o w i n g , c o i n c i d e f o r a s - d e p o s i t e d and a n n e a l e d a-Si:F:H. The f a c t shows t h a t t h e d i p o l a r i n t e r a c t i o n r e m a i n s unchanged a f t e r H e v o l v e s by a n n e a l i n g , w h i c h i n d i c a t e s t h a t t h e d i p o l a r i n t e r a c t i o n b e t w e e n F a n d H d o e s n o t c o n t r i b u t e t o t h e l i n e w i d t h of

r

dKR. T h e r e f o r e , F a n d H a r e c o n s i d e r e d n o t t o b e l o c a t e d c l o s e l y i n a - S i : F : l i .

F NMK s p e c t r a i n a - S i : F d o n o t e x h i b i t t h e m o t i o n a l n a r r o w i n g e f f e c t as shown i n F i g . 3 i n s p i t e o f t h e p r e s e n c e o f a l a r g e amount of S i F 4 o r ( S i F 2 ) , , j u d g i n g from t h e i n f r a r e d a b s o r p t i o n s p e c t r a [ 9 ] . T h e r e f o r e , i t i s s p e c u l a t e d t h a t t h e r e e x i s t S i F 4 o r (SiF2),, g r o u p s which a r e e a s y t o move and t h o s e which a r e n o t e a s y t o move d e p e n d i n g on t h e e n v i r o n m e n t . The i n v a r i a n c e o f t h e F EMR s p e c t r u m f o r a - S i : F w i t h a n n e a l i n g i s c o n s i s t e n t w i t h t h e f a c t t h a t t h e i n f r a r e d a b s o r p t i o n s p e c t r u m d o e s n o t a p p r e c i a b l y c h a n g e w i t h a n n e a l i n g [ l O ] . S i n c e b o t h t h e F NE!R a n d i n f r a r e d a b s o r p t i o n s p e c t r a f o r a-Si:F:K c h a n g e a t t e m p e r a t u r e a t which H e v o l v e s , t h e move- ment of H a t o m s is c o n s i d e r e d t o s t i m u l a t e t h e c h a n g e of F i n c o r p o r a t i o n scheme.

H NP% l i n e w i d t h f o r a-Si:F:H h a s o n l y a s m a l l e f f e c t o f n a r r o w i n g e v e n a t room t e m p e r a t u r e p r e s u m a b l y b e c a u s e t h e f i l m d o e s n o t c o n t a i n a n a p p r e c i a b l e amount o f H

10

l a - S i : ~ : ~ a s d e p . l

A

A a-Si:F:H

600°C

ann

~ 3 0

- ^o

^{rn a-Si:F 600% ann.}

LL n

o 8 a-Si: H

os

dep.

- 0

^{A A} a-Si:F:H as dep.

0 1

I

temperature ( K annealing temperature ( %

F i g . 3 . T e m p e r a t u r e d e p e n d e n c e o f t h e F i g . 4 . Changes w i t h a n n e a l i n g o f t h e l i n e w i d t h of H and F NFIR i n a-Si:H, c e n t e r d e n s i t y Ys o f t h e ESR s i g n a l a-Si:F:H and a - S i : F a s - d e p o s i t e d a n d d u e t o d a n g l i n g b o n d s i n a-Si:H.

a n n e a l e d a t 600°C. a-Si:F:H and a - S i : F .

C4-732 JOURNAL DE PHYSIQUE

i n t h e form o f movable ( S i H 2 X \ . The f a c t is c ~ n s i s t e n t w i t h t h e f a c t t h a t f o r t h i s f i l m t h e i n f r a r e d a b s o r p t i o n p e a k i s m a i n l y a t 2000 cm-' i n d i c a t i n g t h e form o f SiH.

Thus, t h e l i n e w i d t h a t 77 K i s c o n s i d e r e d t o b e o n e w h i c h is f r e e from m o t i o n a l n a r r o w i n g .

I n c o n t r a s t , H MIR l i n e w i d t h f o r a s - d e p o s i t e d a-Si:E e x h i b i t s a p r o m i n e n t e f f e c t o f n a r r o w i n g a t room t e m p e r a t u r e , i n d i c a t i n g t h a t t h e f i l m c o n t a i n s a l a r g e amount o f H i n t h e f o r m O ~ ( S ~ H ~ ) ~ i n a g r e e m e n t w i t h t h e f a c t t h a t t h e i n f r a r e d a b s o r p t i o n p e a k i s m a i n l y a t a r o u n d 2100 cm-' f o r t h i s f i l m . The p r e s e n c e o f t h e l a r g e amount o f H i n t h e f o r m o f (SiH2)n may e x p l a i n t h e l a r c e ESR c e n t e r d e n s i t y i n t h i s f i l m as shown i n F i g . 4 [ 1 1 ] .

I t is f o u n d f r o n F i g s . 1 a n d 4 t h a t t h e i n c r e a s e i n t h e ESR c e n t e r d e n s i t y by a n n e a l i n g c o r r e s p o n d s t o t h e d e c r e a s e i n t h e c o n t e n t o f I! i n a-Si:H a n d a-Si:F:H.

As e x p e c t e d , t h e i n c r e a s e i n t h e ESR c e n t e r d e n s i t y by a n n e a l i n g i s s m a l l f o r h y d r o g e n f r e e a-Si:F. The o r i g i n o f t h e s m a l l i n c r e a s e i n t h e ESR c e n t e r d e n s i t y i s n o t c l e a r , b u t i t m i g h t b e c a u s e d d u r i n g t h e c o o l i n g p r o c e s s a f t e r a n n e a l i n g b e c a u s e a s p e c i a l c a r e was n o t t a k e n t o a v o i d a r a p i d c o o l i n g .

I n c o n c l u s i o n , we m e a s u r e d how t h e NliR o f F and H a n d t h e ESR c h a n g e b y a n n e a l i n g i n a - S i : F , a-Si:F:H a n d a-Si:H. The t e m p e r a t u r e d e p e n d e n c e o f t h e NPR l i n e w i d t h was m e a s u r e d , a n d t h e n o t i o n a l n a r r o w i n g was s e e n i n some c a s e s . The r e s u l t s are c o r r e l a t e d w i t h t h e p r e s e n c e o f ( S i F n ) n o r S i F , and (SiIi2)n w h i c h a r e e a s y t o move. We a l s o f o u n d t h a t h y d r o g e n f r e e a - S i : F i s much more s t a b l e a g a i n s t h e a t i n g t h a n a-Si:H a n d a-Si:F:H.

Acknowledgements.- The a u t h o r s w i s h t o t h a n k K. Nakazawa f o r t e c h n i c a l a s s i s t a n c e . They would a l s o t h a n k D r . Y . Uchida o f F u j i E l e c t r i c C o r p o r a t e R e s e a r c h a n d

Development, L t d . a n d Dr. H . K a t s u m u r a o f Tokyo I n s t i t u t e o f T e c h n o l o g y f o r s u p p l y - i n g a-Si:F:H a n d a - S i : F s a m p l e s , r e s p e c t i v e l y . T h i s work i s s u p p o r t e d by t h e S u n s h i n e F r o j e c t o f H i n i s t r y o f I n t e r n a t i o n a l T r a d e a n d I n d u s t r y of J a p a n .

R e f e r e n c e s

C a r l o s V. E. a n d T a y l o r P. C., Phys. Rev. L e t t .

35

(1980) 356.

Reimer J. A . , Vaughan R . W. a n d K n i g h t s J. C., S o l i d S t a t e Commun.

21

( 1 9 6 1 ) 1 6 1 . Reimer J . A . , Vaughan R . W. and K n i f , h ~ : ; J . C., l'hys. Rev. L e t t .

5

( 1 9 8 0 ) 1 9 3 . Ueda S . , Kumeda I!. a n d S h i m i z u T . , J p n . J . Appl. P h y s .

2

(1951) No. 6 . C a r l o s C1. E. a n d T a y l o r P. C., P r o c . T o p i c a l C o n f . T e t r a h e d r a l l y Bonded Amor- phous S e m i c o n d u c t o r s , C a r e f r e e , A r i z o n a , 1 9 8 1 .

J e f f r e y F. R . , Lowry I!. E., G a r c i a 1:. L. S . , B a r n e s R. G. a n d T o r g e s o n D. E . , i b i d .

Fang C. J . , Ley L . , S h a n k s H. R., G r u n t z K. J . a n d C a r d o n a t!., P h y s . Rev. B

11

( 1 9 8 0 ) 6140.

Lucovsky G., F u n d a m e n t a l P h y s i c s o f Amorphous S e m i c o n d u c t o r s , Ed. F. Yonezawa ( S p r i n g e r - V e r l a g , B e r l i n , 1 9 3 1 ) p. 8 7 .

Flatsumura H., Nakagome Y. a n d Furukawa S . , J . A p p l . P h y s .

52

(1951) No. 1.

E a t s u m u r a H., Nakagome Y . a n d Furukawa S . , J. P h y s . S o c . J p n .

2

( 1 9 8 0 ) S u p p l . A p. 1 2 3 5 .

K n i g h t s J . C., Lucovsky G. a n d Nemanich R. J . , J. Non-Cryst. S o l i d s

2

( 1 9 7 9 ) 393.