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CORRELATION BETWEEN CONDUCTIVITY, ELECTRON SPIN RESONANCE AND OPTICAL
ABSORPTION IN RF SPUTTERED SiO2 FILMS
M. Meaudre, R. Meaudre, J. Tardy, Bernard Tribollet
To cite this version:
M. Meaudre, R. Meaudre, J. Tardy, Bernard Tribollet. CORRELATION BETWEEN CON- DUCTIVITY, ELECTRON SPIN RESONANCE AND OPTICAL ABSORPTION IN RF SPUT- TERED SiO2 FILMS. Journal de Physique Colloques, 1981, 42 (C4), pp.C4-1013-C4-1016.
�10.1051/jphyscol:19814221�. �jpa-00220851�
CORRELATION BETWEEN CONDUCTIVITY, ELECTRON SPIN RESONANCE AND OPTICAL ABSORPTION IN RF SPUTTERED SiOZ FILMS
M. Meaudre
,
R. Meaudre,
J . Tardy*
and B. ~ r i b o l l e t * "Laboratoire de Physique Electronique
x
Dlpartement de Physique des Mate'riaw
**Laboratoire de Spectrorne'trie Ionique e t MoZQcuZaire
U n i o e r s i t l de
Lyon, 43Bd du
11Novembre 1918,
69622ViZZeurbanne, France.
A b s t r a c t . - T h i s a r t i c l e r e p o r t s on c o n d u c t i v i t y
,
ESR and o p t i c a l a b s o r p t i o n s p e c t r a o b t a i n e d on r f s p u t t e r e d Si02 f i l m s.
Measurements performed i n d i f f e r e n t ambiences show t h a t H20 c o n s i d e r a b l y a l t e r s t h e p h y s i c a l p r o p e r t i e s of t h e f i l m s . The f i r s t pumping a f t e r t h e e l a b o r a t i o n of a f i l m r e d u c e s b o t h , t h e c o n d u c t i v i t y and t h e t o t a l ESR s i g n a l - w h i l e t h e o p t i c a l a b s o r b a n c e i s i n c r e a s e d.
When wet a i r i s a g a i n a d m i t t e d t h e c o n d u c t i v i t y r a p i d l y i n c r e a s e s w h i l e ESR and o p t i c a l spec- t r a a r e unchanged.
It i s concluded t h a t c h a r g e c a r r i e r s a r e i n t r o d u c e d by H 0 i n d e p e n d e n t l y of i n t r i n s i c d e f e c t s.
Complementary e x p e r i m e n t s a r e s u g g e s t e d t o 2 i n v e s t i g a t e t h e p o s s i b l e i n f l u e n c e o f i n t r i n s i c d e f e c t s on t r a n s p o r t phenomena.
I n t r o d u c t i o n . - The b e h a v i o r o f r f s p u t t e r e d SiO f i l m s s u b m i t t e d t o a c and d c e l e c - t r i c f i e l d s i n a l a r g e t e m p e r a t u r e r a n g e ( 7 7 - 5 7 3 ~ ) h a s allowed l i g h t t o be shed on t r a n s p o r t mechanisms [ 1 , 2 , 3 ] . But e l e c t r i c a l measurements o n l y , have been p r o v i n g i n - s u f f i c i e n t t o d e t e r m i n e c a r r i e r s and c e n t e r s r e s p o n s i b l e f o r c o n d u c t i o n . With t h e l n t e n t of s p e c i f y i n g t h e n a t u r e of t h e l a t t e r , a b s o r p t i o n and ESR s p e c t r a were s t u - d i e d i n t h e same ambiences and t e m p e r a t u r e s ; c o r r e l a t i o n between e l e c t r i c a l and op- t i c a l measurements a r e t h e f o c u s o f a t t e n t i o n i n t h e p a p e r
.
C h a r a c t e r i z a t i o n . - A s t h e o b j e c t of t h i s s t u d y i s t o f u r t h e r e x p l o r e t h e knowledge o f c e n t e r s a r i s i n g i n c o n d u c t i o n
,
i t i s i m p o r t a n t t o w e l l d e f i n e our r f s p u t t e r e d S i 0 2 f i l m s.
The method o f helium i o n b a c k - s c a t t e r i n g a n a l y s i s [ 4 ] was u s e d t o d e t e r - mine t h e s t o i c h i o m e t r y of o u r f i l m s , one example o f t h e s p e c t r a o b t a i n e d i s g i v e n i n f i g u r e 1. Both s l i g h t l y oxygen-rich and s l i g h t l y o x y g e n - d e f i c i e n t f i l m s o c c u r , t h ecomposition of o u r samples v a r i e d between SiO 1.95 and Si02
R3.
Analogous r e s u l t s were found by o t h e rWOE
e r s [ 5 ] .IR s p e c t r a and Na p r o f i l e s (de-8 6 1 -
C
r i v e d from i o n m i c r o p r o b e a n a l y s i s ) o b t a i n e d on o u r f i l m s a r e g i v e n i n r e f .2
.
5 6 0
9
: B a c k s c a t t e r i n g s p e c t r u m produced by
0 , 7 4 2 1 , 1 4 4 El:!t'Jl
silicon h r g o n 2 MeV He i o n s s c a t t e r e d a t 160' from SiOx.x=2.03
Carbon Oxygen
R e s u l t s . -
E l e c t r i c a l ~ a s u r e m e n t s
... . -
They = r e p e r f ormedin v a r i o u s atmospheres : d r y and wet a i r (ambient a i r ),
hydrogen, vacuum.
The f i l m s have s i m i l a r t r a n s p o r t p r o p e r t i e s f o r t h e p r e v i o u s l y i n d i c a t e d s t o i c h i o m e t r y r a n g e.
F i g u r e 2 shows t h a t i m p o r t a n t changes of t h e c o n d u c t i v i t y 3 a r e o n l y o b s e r v e d a f t e r e x p o s u r e t o wet a i r.
The p r e s e n c e o f H20 c a u s e s a r a p i d a $ i s e o f o,
which can be r e v e r s e d by removing w a t e r by pum- p i n g . (The c o n d u c t i v i t y o i s % f e c t e d by H20 i n t h e same s e n s e ).
These e f f e c t sd c
w e r e o b s e r v e d - o n a s - s p u t t e r e d and 573K a n n e a l e d s a m p l e s , t h i s c o u l d b e e v i d e n c e of m i c r o v o i d s
[
61 .
Complementary e x p e r i m e n t s have emphasized t h a t t h e v a r i a t i o n of c o n d u c t i v i t y i s a b u l k and n o t a s u r f a c e e f f e c t.
70 h a s been measured i n t h e f r e q u e n c y r a n g e 40-10 Hz and t e m p e r a t u r e r a n g e 77 - 5 % ~
.
F i g . 3 [ l ].
For T > 320K t h e c o n d u c t i v i t y obeys a n e q u a t i o n of t h e formOat
= A W ~ where t h e q u a n t i t y s i s l i n e a r l y t e m p e r a t u r e dependent c l o s e t o,
b u t Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19814221C4-1014 JOURNAL DE PHYSIQUE
Fig.2:Change of conductance r e s u l t i n g from pumping and e x p o s u r e t o d i f f e r e n t atmospheres
.
Au-SiO -Au c o n f i g u r a t i o n , a r e a of c o n t a c t s 3.12 mm2,film t h i c k - n e s s 42001 .
Fig.!:Ac c o n d u c t i v i t y v e r s u s f r e q u e n c y Au-S10 -Au c o n f i g u r a t i o n
,
f i l m t h i c k - n e s s 4300; .
1:i1,,, a<.sl>,,tl~,?<l 0, 290 l<, 760 toe.?
0. 200 I i , 10 6 ;,;I.v
Film i):>#?~iilcd for 7 2 llctlira al. :Is9 l< i n t ~ l t ' .
v . 3S9 K , ln-'t,ni A. B10 l<. 10-Vori
a, ii l<, > W 6 tor:
l e s s t h a n u n i t y
.
Below 320K ,Gac i s a l m o s t t e m p e r a t u r e independent w i t h s Q 1.
Thep o s s i b l e t r a n s p o r t mechanisms h a v e been d i s c u s s e d [ l ] and i t a p p e a r e d t h a t r e s u l t s were r e a s o n a b l y w e l l e x p l a i n e d by hopping o f c a r r i e r s between l o c a l i z e d s t a t e s o v e r b a r r i e r s
.
F i g u r e 4 shows I n J v e r s u s F i n t h e t e m p e r a t u r e r a n g e 77-357K f o r e l e c t r i c f i e l d s up t o 9.107 ~ m - l
.
T h i s f i g u r e emphasizes non l i n e a r c u r r e n t v o l t a g e c h a r a c t e r i s t i c s two a c t i v a t i o n e n e r g i e s of a b o u t 0 . 3 eV a n d 0 . 0 3 eV have been n o t e d i n t h e h i g h and low t e m p e r a t u r e r a n g e s r e s p e c t i -4 -
v e l y
.
Among t r a n s p o r t mechanisms /e n v i s a g e d 131 t h e most p r o b a b l e o n e is c a r r i e r hopping between d e f e c t s t a t e s b u t w i t h d e f o r m a t i o n o f s u r - r o u n d i n g s
.
F i g . 4 : C u r r e n t d e n s i t y v e r s u s e l e c - t r i c f i e l d .Au-Si02-Au c o ~ f i g u r a - t i o n , f i l m t h i c k n e s s 2200 A
.
S o l i d l i n e s r e f e r t o measurements performed under vacuum ( I O - ~ T o r r ) a t t h e i n d i c a t e d t e m p e r a t u r e s
1 2 3 4 5 6 1 a
ESR and 2 t i c a l measurements.- As in t h e s t u d y of e l e c t r i c p r o p e r t i e s
,
vacuum h a s---m ---m-
been broken between f a b r i c a t i o n and measurements
.
A b s o r p t i o n s p e c t r a were measured w i t h a Cary 17 s p e c t r o m e t e r and ESR s p e c t r a were o b t a i n e d w i t h a V a r i a n V4502-12 s p e c t r o m e t e r i n t h e X band (9.8 GHz).
F i g u r e 6 r e p r e s e n t s ESR s p e c t r a a f t e r d i f f e r e n t t r e a t m e n t s
.
F i g u r e 7 shows o p t i c a l s p e c t r a
,
t h e two bands a t 5.4 eV and 6.2 e V were o b s e r v e d p r e v i o u s l y i n r f s p u t t e r e d SiOZ f i l m s which had undergone o t h e r t r e a t m e n t s [ 71 .
Figs.5-6:Room t e m p e r a t u r e ESR s p e c t r a ( e x c e p t s p e c t r a 1 7 , 1 8 , 2 0 , 2 1 performed a t 1305C) I n f l u e n c e of d i f f e r e n t t r e a t m e n t s e x e c u t e d i n t h e o r d e r :
I Ambient a i r ( a f t e r 15 d a y s a t ambient a i r )
=Ambient a i r ( a f t e r 3 months a t ambient a i $
~ V ~ C U U ~ ( a f t e r 30 h o u r s i n vacuum) E A m b i e n t a i r ( a f t e r 1 day a t ambient a i r ) P Vacuum ( a f t e r 2 d a y s i n vacuum)
PIAmbient a i r ( a f t e r 15 h o u r s a t a m b i e n t a i 3
Fig.7: Room t e m p e r a t u r e o p t i c a l a b s o r p t i o n s p e c t r a
.
I n f l u e n c e o f d i f f e r e n t t r e a t m e n t s . F i l m t h i c k n e s s - 3v .
C4-1016 JOURNAL DE PHYSIQUE
Summary o f r e s u l t s . - For s h o r t n e s s
,
a b s o r b a n c e and ESR s i g n a l w i l l b e c a l l e d OD--- ---
( O p t i c a l D e n s i t y ) and ESR
,
r e s p e c t i v e l y.
A summary o f o u r e x p e r i m e n t a l r e s u l t s i s a s f o l l o w s :
1) When a s - s p u t t e r e d S i 0 2 f i l m s a r e exposed f o r 3-4 months t o ambient atmosphere it i s found t h a t OD remains unchanged, ESRY ( f i g . 6 c u r v e s
1,111
and U#.2) Vacuum b e i n g broken between f a b r i c a t i o n and e x p e r i m e n t a l s t u d i e s
,
i t i s o b s e r v e d d u r i n g t h e f i r s t m i n u t e s f o l l o w i n g t h e f i r s t pumping,
t h a ta
( f i g . 2 ) w h i l e OD i s unchanged ( f i g . 7 ) ,(E.SR was n o t s t u d i e d ).
During t h e f o l l o w i n g h o u r s i n vacuum,
O D f , ESR\ and G\
.
3) Thermal t r e a t m e n t s a t 573K (OD a n d b ) o r 403K (ESR) i n vacuum d u r i n g some h o u r s l e a d t o OD \ ( f i g . 7)
,
ESRG
( f i g . 6 c u r v e s 19,20) and a \ ( f i g . 3 ) .4) Exposure a g a i n t o ambient a i r a f t e r pumping o r t h e r m a l t r e a t m e n t i s f o l l o w e d by a r a p i d (some m i n u t e s ) i n c r e a s e o f @ when no v a r i a t i o n of OD and ESR a r e o b s e r v e d o v e r s e v e r a l d a y s
.
Exposure t o H2 o r O2 h a s no i n f l u e n c e on 5,
OD and ESR.
D i s c u s s i o n . - From t h e o b s e r v a t i o n 2) it would seem t h a t t h e s l o w v a r i a t i o n o f b a n d of t h e t o t a l ESR s i g n a l o b s e r v e d d u r i n g some h o u r s a f t e r t h e f i r s t pumping a r e con- n e c t e d
.
When v a n i s h i n g,
some p a r a m a g n e t i c c e n t e r s c o u l d g i v e r i s e t o o p t i c a l l y a c t i v e c e n t e r s.
According t o Holzenkampfer e t a l . L81 t h e E' c e n t e r s do n o t c o n t r i - b u t e t o hopping t r a n s p o r t.
Furthermore t a k i n g t h e microwave power l e v e l s u s e d i n t h i s work i n t o a c c o u n t,
it is p r o b a b l e t h a t t h e E ' s i g n a l h a s n o t been r e s o l v e d [ 9 1 b u t r a t h e r t h e ESR s i g n a l s r e s u l t i n g from some m i x t u r e of E' c e n t e r s,
n o n - b r i d g i n g oxygen t r a p p e d h o l e c e n t e r s and hydrogen a s s o c i a t e d d e f e c t centersl10-121 have been observed.
The h y p e r f i n e d o u b l e t w i t h - 116 G s p l i t t i n g c o u l d b e due t o t h e l a s t d e f e c t [12,13], its i n t e n s i t y d e c r e a s e s when pumped o r h e a t e d i n vacuum ( f i g . 6 c u r v e s 6 a n d 11).
O b s e r v a t i o n s 2) and 4) show t h a t ambient a i r m o d i f i e s c o n d u c t i v i t y r a p i d l y b u t n o t o p t i c a l and ESR s p e c t r a
.
It i s s u g g e s t e d t h a t c h a r g e c a r r i e r s a r e i n t r o d u c e d inde- p e n d e n t l y of i n t r i n s i c d e f e c t s of f i l m s.
It i s p o s s i b l e t h a t t h e c u r r e n t p a s s e s t h r o u g h OH c e n t e r s i n t h e n e t w o r k [ l 41 .
A s o u r a n n e a l e d f i l m s have a l o s s t a n g e n t t a n 6 of t h e o r d e r o f t h a t o b s e r v e d i n t h e r m a l l y grown S i 0 2 f i l m s [ l , l 5]
i t maybe a s k e d whether t h e low r e s i d u a l c o n d u c t i v i t y o b s e r v e d i n t h e s e two t y p e s of f i l m s a r e due t o r e s i d u a l H 2 0 o r t o i n t r i n s i c d e f e c t s
,
p a r a m a g n e t i c o r n o t.
I n v e s t i g a t i o n s concerniilg t h e p o s s i b l e i n f l u e n c e on ESR s p e c t r a and c o n d u c t i v i t y , o f t h e i n t r o d u c t i o n o f a t o m i c hydrogen i n o u r f i l m s a r e p r e s e n t l y i n p r o g r e s s i n o u r group
.
R e f e r e n c e s
1 MEAUDRE M. and MEAUDRE R., P h i l . Mag. 40 (1979) 401
.
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3 MEAUDRE R. and MEAUDRE M , , t o b e p u b l i s h e d i n J . n o n - c r y s t a l l i n e S o l i d s
.
4 MAYER J . W . and NICOLET M.A., M a t e r i a l C h a r a c t e r i z a t i o n Using I o n Beams
,
ed. by J.P. Thomas and A . Cachard (New York,Plenum P r e s s ) 1978 p.333.
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7 HICKMOTT T.W., J. Appl. Phys. 42 (1971) 2543
.
8 HOLZENKAMPFER E., RICHTER F.W., STUKE J . , and VOGET-GROTE U . , J n o n - c r y s t a l l i n e S o l i d s 32 (1979) 327
.
9 GRISCOM D.L., SIGEL G.H. Jr and FRIEBELE E. J. , P r o c . Z i I n t . Cong.Glass ,Praguea97>p3 10 GRISCOM D.L., J . n o n - c r y s t a l l i n e S o l i d s 31 (1978) 241
11 FRIEBELE E. J. and GRISCOM D.L.
,
T r e a t i s e on M a t e r i a l s S c i e n c e and ~ e c h n o l o ~ ~ ,vol.$G l a s s l t : e d s M.TOMOZAWA and R.H.DOREMUS (Academic Press,New York,1979) p.257 12 GRISCOM D.L., J. n o n - c r y s t a l l i n e S o l i d s 40 (1980) 241
.
13 VITKO J . J r , J . Appl. Phys. 49 (1978) 5530
.
14 MOTT N . F . , S r o c . Roy. Soc. A 1981 ( i n p r e s s )
15 CHERNYAEV V.N. and KORZO V.F., Thin S o l i d F i l m s 37 (1976) L.63
