CHEMICAL SITES OF RARE GAS ATOMS IN
AMORPHOUS SILICON
Y. Katayama, T. Shimada, K. Usami, E. Maruyama
To cite this version:
Y. Katayama, T. Shimada, K. Usami, E. Maruyama. CHEMICAL SITES OF RARE GAS
ATOMS IN AMORPHOUS SILICON. Journal de Physique Colloques, 1981, 42 (C4), pp.C4787-C4-790. <10.1051/jphyscol:19814172>. <jpa-00220797>
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JOURNAL DE PHYSIQUE
Co1Zoqv.e C4, suppldment au nO1O, Tome 4 2 , octobrae 1981
page
C4-787
C H E M I C A L S I T E S OF RARE G 4 S ATOMS I N ANORPHOUS S I L I C O N
Y . Katayama, T . Shimada, K. Usami and E . Maruyama
Cenfrul H e s e ~ r c hLaboratory, Hitachi, J,td.,
Kokubunji, Tokyo 185, Japan
A b s t r a c t . - The c h e m i c a l s i t e s o f t h e neon a t o m s imbedded i n h y d r o a e n a t e d
amorphous s i l i c o n a-Si:H r h a t i s p r o d u c e d u s i n g Ne a s a s ~ u t t e r i n ga g e n t
a r e examined u s i n g X-ray p h o t o e l e c t r o n s p e c t r o s c o p y (XPS). From t h e beh a v j o u r o f t h e XPS s p e c t r a i n t h e Ne KLL Auger e n e r a y r e g i o n , it i s r e v e a l cc: t h a t t h e Ne a t o m s i n c o r p o r a t e d i n a-Si:II a r e ir:?bedded, i n t h r e e k i n d s o f
s i t c s , i . e . . i n s i t e s c l o s e l y s u r r o u n d e d by S i a t o m s , i n s i t e s a d l a c e n t
t o i n c o r p o r a t e d hydrogen atoms, and i n microvoids.
I n t r o d u c t i o n . - I t i s well-known t h a t h y d r o g c n a t e d amoruhous s i l i c o n a-Si:H p r o C u c e d
o f t c r : c e n t a i n s a c o n s i d e r a b l e amount o f rare g a s a t o m s u s e J a s s p u t t e r The amount s o m e t i m e s r e a c h e s s e v e r a l a t o m i c 8 [ 2 , 3 ] . T h i s means
ing a a c n t s [l-31.
t h a t , on t h e a v e r a g e , o n e o i t h e n e x t - n e a r e s t n e i g h b o u r s o f e a c h S i atom i s a r a r e
I t i s w r o b a b l e t h a t t h e n r e s e n c e o f s u c h a l a r a e amount o f r a r e g a s a t o m s
aas aton.
a f f e c t s b o t h s t r u c t u r a l a n d e l e c t r o n i c p r o p e r t i e s o f a-Si:H.
However, a l n o s t n o t h i n g
i s known c o n c e r n i n g t h e s i t c s i n w h i c h t h e r a r e Gas a t o m s a r e i n c o r p o r a t e d .
by s : , u t t c r i n g
To e x a m i n e ho;; much a n d i n w h i c h s i t e s t h e r a r e g a s a t o m s a r e imbcdde-l i n a-Si:H
m e a s u r e m e n t s w e r e made w i t h a-Si:II pr:>duce"y
X-rav p h o t o e l e c t r o n s ~ e c t r o s c o w (XPSJ
~
r e a c t i v e s p u t t e r i n g u s i n a Ne, A r a n d Xe a s s p u t t e r i n g a a e n t s .
Neon, t h e l i g h t e s t
e l e m e n t amonc: t h e s e a a s e s , was i n c o r p o r a t e d i n t o t h e d c w o s i t e d a-Si::; t o t h e a r e a t e s t
amount.
I n a p r e v i o u s r e p o r t , t h e amount o f i n c o r p o r a t e d Ne a t o m s was a i v e n t o b e a
f u n c t i o n o f t h e p r e p a r a t i o n c o n d i t i o n s , a s d e t e r m i n e d by XPS m e a s u r e r . e n t s [ 3 1 .
I n t h i s p a p e r , t h e c h e m i c a l s i t e s o f t h e Ne a t o m s i n c o r r 7 o r a t c d i n a-Si:H a r c
examined u s i n a t h e XPS s p e c t r a v a r i a t i o n s f o r a - S i : H i n t h e Ne KLL A u c e r t r a n s i t - i o n
energv r e c i o n t h a t r e s u l t from a s e r i e s o f s u c c e s s i v e h c a t t r e a t m e n t , and with t h e
sic: o f t h e r m a l e f f u s i o n m e a s u r e m e n t s 141.
E x w c r l m e n t a l . - Hydroc:enated amorphous s i l i c o n a - S i : H f i l m s w e r e d e p o s i t e d o n c r v s t a l l i n e s i l i c o n s u b s t r a t e s h y a d i o d e - t y p e r e a c t i v e s p u t t e r i n a method.
The s n u t t e r i n g
amb.i.ent was a g a s m i x t u r e o f 9 3 rb Ne a n d 7 % H . The t o t a l g a s p r e s s u r e was c h o s e n
t o b e 0 . 2 5 P a . , s o t h a t a s u b s t a n t i a l amount o$ Ne a t o m s micrht b e i n c o r : > o r a t e d i n t h e
a - S i : H [ 3 ] . To e l u c i d a t e t h e i n f l u e n c e o f h y d r o g e n g a s on t h e i n c o r n o r a t i o n o' Ne
atoms, specimens w i t h o u t hydroaen were a l s o prepared.
Thc XPS s , e c t r a w e r e t a k e n w i t h a Vacuum G e n e r a t p f s ADES 400 s y s t e m .
The b a s e
p r e s s u r e o ? t h e a n a l y s e r chamber was l e s s t h a n 3 x 10Torr.
To m i n i m i z e t h c i n f l u e n c e o f n a t i v e o x i d e a t t h e s a m p l e s u r f a c e , t h e s a m p l e was e t c h e d w i t h a 5 P, HF s o l u t i o n f o r 1 5 s j u s t b e f o r c b e i n a s e t i n t h e vacuum chamber.
The r e s o l u t i o n o f t h e
a n a l v s i n g s - , s t e m was c h e c k e d w i t h t h e l i n e - w i d t h o f t h c XPS p e a k from t h e Au-4f
7/2
o f t h i s weak was 1.1 eV.
core level.
The f u l l - w i d t h a t half-maximum (t'WII:'.)
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19814172
JOURNAL DE PHYSIQUE
C4-788
- F i g u r e 1 shows XPS s p e c t r a i n t h e Ne KLL Auger t r a n s i t i o n e n e r a y r e g i o n
f o r amornhous s i l i c o n f i l m s .
I n t h i s f i g u r e , ( a ) i s f o r a-Si:II(Ne) w l t h hvdrogen and
( b ) f o r a - S i ( N e ) w i t h o u t hydroaen.
T h e i r v a r i a t i o n s due t o s u c c e s s i v c i n - s i t u h e a t
t r e a t m e n t a r c a l s o shown.
The XPS s p e c t r u m f o r t h e as-arown f i l m w i t h o u t h y d r o n e n h a s
t w o r w a k s , r>eak A a t 8 1 9 a n d p e a k C a t a b o u t 8 1 4 eV. The s p e c t r u m f o r t h e f i l m w i t h
h v d r n g e n c o n t a i n s a n o t h e r component B, which i s a t a b o u t 8 1 6 eV, i n a d d i t i o n t o t h e
two p e a k s .
The intensities o f A a n d B p e a k s d e c r e a s e w i t h t h e i n c r e a s e i n h e a t i n g
t e m ~ e r a t u r e . The nenk C a t 8 1 4 eV n e r s i s t s e v c n a f t e r h c a t i n g u p t n 7 0 0 ' ~ .
The d i f f e r i n q b e h a v i o u r f o r t h e t h r e e ~ e a k st h a t r e s r l l t s from h e a t t . r e a t m e n t s u g a c s t s t h a t
t h e t h r e e p e a k s art= a t t r i b u t a b l e t o t h e N e a t o m s i n t h r c c d i f f e r e n t k i n d s of s i t e s .
I n o a r t i c u l a r , p e a k B, w h i c h i s s e e n o n l y f o r s ~ e c i m c n sw i t h h y d r o g e n , i s t h o u q h t t o
come f r o n h y d r o a e n - a s s o c i a t e d s i t e s .
R esults.
-
I
840
830
L
I
820
810
KINETIC ENERGY (eV)
1
800
l - l - L l A
840
830
820
810
800
KINETIC ENERGY (eV)
(a)
(b)
V a r i a t i o n o f XPS s p e c t r a i n Ne KLJ. Augcr t r a n s i t i o n
e n e r g y r e g i o n due t o s u c c e s s i v e h e a t t r e a t m e n t o f ( a )
a - S i :H(Ne) w i t h h y d r o g e n a n d ( b ) a - S i (:Je) w i t h o u t hydrogen.
Broken l i n e s i n ( a ) d e n o t e c o r r e s p o n d i n g p e a k p o s i t i o n i n (b).
Fig.1 :
-
XPS s p e c t r a i n t h e N e - l s , - 2 s a n d -2p b i n d i n q e n e r g y r e g i o n s , o n t h e c o n t r a r y ,
h a d s i n g l e p e a k s whose e n e r g y p o s i t i o n s w e r e i d e n t i c a l f o r b o t h s p e c i m e n s w i t h a n d
without hydrogen, w i t h i n t h e accuracy o f t h e p r e s e n t experiment.
The s h a p e s 02 t h e s e
peaks d i d n o t change a p p r e c i a b l y with t h e h e a t treatment.
I t i s i n t e r e s t i n g t h a t t h e i n f l u e n c e o f c n v i r o n m c n t o n t h e imbedded r a r e g a s
a t o m s is s e e n o n l y i n t h e Auger s p e c t r a w h e r e two f i n a l h o l c s a r e i n v o l v e d a s t h c
f i n a l s t a t e s o f Auger t r a n s i t i o n .
I t is h a r d l y s e e n i n t h e s i m p l e c o r e l e v e l p h o t o emission spectra.
To s u p p l e m e n t t h e s e s p e c t r o s c o p i c m e a s u r e m e n t s , a t h e r m a l e v o l u t i o n e x ~ c r i m e n t
was a l s o p e r f o r m e d [ 4 1 .
I n F i g . 2 , t h e number o f Nc ( s o l i d l i n e ) a n d h y d r o q e n ( b r o k e n
l i n e ) a t o m s e v o l v e d f r o m t h e u n i t volume o f a s a m p l e a r e p l o t t e d a s f u n c t i o n s o f h e a t
treatment tempcrature.
Two p e a k s a r c s e e n f o r Ne effusion, o n e a r o u n d 4 0 0 ° c a n d t h e
o t h e r a t a r o u n d 8 0 0 " ~ . The l o w e r t e m p e r a t u r e e v o l u t i o n p e a k c o r r e s p o n d s t o t h e e v o l u t i o n o f hydrogen, and t h e h i g h c r temperature peak corresponds t o t h e c r y s t a l l i z a t i o n
o f amorphous s i l i c o n .
F o r samples w i t h o u t hydrogen, o n l y t h e h i g h e r t e m p c r a t u r e peak
I t i s n o t i c e a b l e t h a t t h e peak B i n Fig.1 d i s a p p e a r s w i t h t h e h e a t
was o b s e r v e d .
t r e a t m e n t above t h i s hydrogen e v o l u t i o n t e m p e r a t u r e , which s u g g e s t s t h a t t h e peak B
i s r e l a t e d w i t h t h e i n c o r p o r a t i o n o f hydrogen.
f 1
'
\+
1 8 eV
!
45.v
1
K I N E T I C ENERGY
VACUUM LEVEL
,
I
PHOTON ENERGY
hv
F i g . 2 : Number o f Ne and
atoms e v o l v e d from
H
a-Si:H(Ne) f i l m by
successive heat t r e a t ments
.
?p
L2,3
P P L I
-,
K I N E T I C ENERGY
T-
B I N D I N G ENERGY
F i g . 3 : Schematic i l l u s t r a t i o n of
-
( a ) p h o t o e m i s s i o n a n d ( b ) Auger
t r a n s i t i o n p r o c e s s e s i n a Ne
atom imbedded i n a-Si:H.
-
Discussion.
I n a n Auger t r a n s i t i o n i l l u s t r a t e d i n F i g . 3 , where a n i n i t i a l h o l e i n
shell,
t h e K - s h e l l d e c a y s by a n n i h i l a t i o n w i t h a l e s s e r bound e l e c t r o n s from t h e L2
s h e l l i s s i m u l t a n e o u s l y e j e c t e d i n t o t h e Gacuum,
a n d a n o t h e r e l e c t r o n from t h e L
2,3
t h e Augcr e n e r g y i s g i v e n by
, observed i n t h e photoemission
L2
p r o c e s s e s [8-101.
Hcre, EHH i s t h e t o t a l i n t e r a ~ g i o nenergy o f t h e L
L
double
2.3 2 , 3
is t h e a d d i t i o n a l p o l a r i z a hole s t a t e i n a particular multiplet configuration, E
u s i n g o n e e l e c t r o n b i n d i n g e n e r g i e s , Els
and E
POI,
t i o n e n e r g y o f t h e l a t t i c e t h a t i s due t o t h e p r e s e n c e o f t h e two f i n a l h o l e s , and
W i s t h e work f u n c t i o n o f t h e f i l m .
Energy s e p a r a t i o n between p e a k s A and C i n F i g . 1 is c l o s e t o e n e r g y s p l i t t i n g
3.7 cV between m u l t i p l e t s t r u c t u r e s due t o t h e i n t c r a c t i o n o f two f i n a l h o l e s i n a
However, t h i s a s s i g n m e n t
s i n g l e Ne atom, which was o b s e r v e d f o r g a s e o u s Ne [5-71.
c a n be e x c l u d e d b e c a u s e t h e i n t e n s i t y r a t i o o f t h e two p e a k s c h a n g e s w i t h h e a t t r e a t ment. Moreover, t h e r a t i o of peak i n t e n s i t i e s f o r m u l t i p l e t i n g a s e o u s Ne is much
l a r g e r t h a n t h o s e s e e n i n F i g . 1 [5,61. I t is, t h e r e f o r e , p r o b a b l e t h a t t h c t h r e e
p e a k s a r e a t t r i b u t a b l e t o t h r e e d i f f e r e n t k i n d s of Ne s i t e s i n amorphous s i l i c o n .
I n t h e Auger e n e r g y g i v e n by E q . ( l ) , t h e t e r m which p r o v i d e s a different c o n t z i b u t i o n , depending o n t h e d i f f e r i n g c h e m i c a l environment, i s t h e 2 o l a r i z a t i o n e n c r g y
o f t h e l a t t i c e , EpOL.
A c t u a l l y , t h e p o l a r i z a t i o n e n e r s y , E POL, o f s e v e r a l e l e c t r o n
On t h e
v o l t s depending upon t h e d i f f e r i n g c h e m i c a l environment was r e p o r t e c [8-101.
o t h e r hand t h e c h e m i c a l s h i f t of o n l y a f r a c t i o n o f one e l e c t r o n v o l t was s e e n i n
These amount become s m a l l e r a s t h e h o s t
o n e e l e c t r o n p h o t o e m i s s i o n s p e c t r a [8,91.
environment becomes l e s s p l a r i z a b l e .
Thus, t h e e n e r g y s h i f t due t o p o l a r i z a t i o n i s o f t h e same o r d e r a s t h e energy
I t would n o t be t o o nuch t o assume
s e p a r a t i o n s among t h e o b s e r v e d A , B and C p e a k s .
t h a t t h e o b s e r v e d t h r e e p e a k s a r e c a u s e d by d i f f e r e n t c o n t r i b u t i o n s o f =he term E
POL
o f t h e Ne a t o m s , imbedded i n d i f f e r e n t c h e m i c a l s i t e s . A s l i k e l y c a n d i d a t e s , o n e may
e a s i l y t h i n k o f t h e t h r e e k i n d s o f Ne s i t e s i l l u s t r a t e d i n F i g . 4 .
There, t h e A peak
i s a s s i g n e d t o t h e Ne a t o m s c l o s c l y s u r r o u n d c d by Sj. a t o m s w h e r e t h e p o l a r i z a t i o n
e n e r g y is t h e l a r g e s t , t h e p e a k C t o t h e N e a t o m s i n t h e m i c r o v o j . d s w h e r e n o p o l a r i z a t i o n e n e r g y i s c x y e c t e d , a n d t h e p e a k B t o t h e Ne a t o m s a d j a c e n t t o t h e i n c o r p o r a t e d
h y d r o g e n a t o m s w h e r e t h e p o l a r i z a t i o n e n e r g y is i n t e r m e d i a t e b e c a u s e t h e p o l a r i z a b i l i t y o f t h e h y d r o g e n a t o m is s m a l l e r t h a n t h a t f o r t h e S i a t o m , a n d is l a r y c r t h a n
t h a t f o r t h e vacuum.
T h i s a s s i g n e m e n t is s u p p o r t e d b y t h e f a c t t h a t t h e A a n d C p e a k s a r e o b s e r v e d
i n t h e b o t h specimens w i t h and w i t h o u t hydrogen a n d t h a t t h e B peak i s o b s e r v e d o n l y
i n t h e specimens with hydrogen.
Fig.4
: S c h e m a t i c i l l u s t r a t i o n o f t h e s i t e s o f inbedded Nc a t o m ,
( a ) Ne atom c l o s e l y s u r r o u n d e d b y Si a t o m s
( b ) N e atom a d j a c e n t t o i n c o r p o r a t e d h y d r o g e n a t o m s
( c ) NC a t o m s i n m i c r o v o i d s .
C o n c l u s i o n . - The c h e m i c a l sites o f N e a t o m s i n c o r p o r a t e d i n h y d r o g e n a t e d amorphous
s i l i c o n h a s b e e n e x a m i n e d u s i n g XPS s p e c t r a i n t h e Ne KLL Auger e n e r g y r e g i o n .
Acknowledgement. - The a u t h o r s arc g r c a t f u l t o D r s . Yoshimasa Murayama, Y a s u h i r o
S h i r a k i , a n d K e i s u k e L. I . K o b a y a s h i f o r e n l i g h t e n i n g d i s c u s s i o n .
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