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Thin Solid Films, 42

(19 77 ) 185 191

{~ Elsevier Sequo ia S .A., Lausa nne Pr in ted in the Neth er lands 185

S P U T T E R I N G O F M E T A L S I N T H E P R E S E N C E O F R E A C T I V E G A S E S

J H R B E K

Czechos lova k Acad emy o f Sc iences , The J . Heyrovsk ); Ins t i tu te o f Phys ical Chem is t ry and Elec -

t rochemis t ry , Mf ichova 7 , 12138 Praha 2 , Vinohrad y Czech os lovak ia)

(Received July 5 , 1976; accepted Octo ber 15, 1976)

T h e s p u t t e r i n g y ie ld s o f T i , T a , M o a n d W b o m b a r d e d b y A r i o n s w e r e

m e a s u r e d

n s tu

b y a w e i g h t lo s s m e a s u r e m e n t a s a f u n c t i o n o f t h e p a r t i a l p r e s s u r e

o f r e a c ti v e ga s ( 0 2 o r N 2 ) . T h e s p u t t e r i n g y i e ld s d e c r e a s e d t o a b o u t 0 . 4 - 0 . 1 o f t h e

i n it ia l v a l u e i n t h e p r e s e n c e o f a r e a c t i v e ga s f o r e v e r y g a s - t a r g e t c o m b i n a t i o n

s t u d i e d . A l l t h e c u r v e s w e r e o f s ig m o i d a l s h a p e w i t h a n i n f le c t io n p o i n t t h a t

d e p e n d e d o n t h e p r i m a r y i o n c u r r e n t d e n s it y .

T h e r e su l ts w e r e i n t e rp r e t e d i n t e r m s o f a m o n o l a y e r c h e m i s o r p t i o n o f t h e

r e a c t i v e g a s o n t h e t a r g e t s u r f a c e u s i n g t h e a s s u m p t i o n t h a t t h e a c t u a l s p u t t e r i n g

y i e ld c a n b e e x p r e s s e d a s a li n e a r c o m b i n a t i o n o f t h e s p u t t e r i n g y i e ld o f th e c l e a n

t a r g e t a n d t h e s p u t t e r i n g y i e l d o f th e t a r g e t c o v e r e d w i t h t h e a d s o r b e d l a y e r.

1. INTRODUCTION

T h e e f fe c t o f g a se o u s i m p u r i t ie s o n t h e p r e p a r a t i o n o f t h i n f il m s b y s p u t t e r i n g

w a s r e c o g n i z e d a l o n g t im e a g o 1 '2 . M o r e r e c e n t ly W e h n e r 3 a n d Y o n t s a n d

H a r r i s o n 4 f o u n d t h a t t h e s p u t te r i n g y i e ld f o r b o t h l o w a n d h i g h e n e r g y w a s a f fe c t ed

b y o x y g e n o r r e a c t i v e g a s a d s o r p t i o n . I n s o m e r e c e n t p a p e r s t h e i m p o r t a n c e o f t h e

p h y s i c o c h e m i c a l p r o p e r ti e s o f th e g a s - t a r g e t c o m b i n a t i o n d u r i n g r e a c ti v e sp u t t e r-

i n g w a s d i s c u ss e d 5 -1 2. T h e i n t e r a c t i o n b e t w e e n t h e r e a c t i v e g a s m o l e c u l e s a n d t h e

s u r f a c e a t o m s o f t h e ta r g e t is o f b as i c i m p o r t a n c e w i t h r e s p e c t t o t h e n a t u r e a n d

m e c h a n i s m o f t h e s p u t t e r i n g p r o c es s . T h i s h a s b e e n t a k e n i n t o a c c o u n t i n r e c e n t ly

p u b l i s h e d m o d e l s o f r e a c t i v e s p u t t e r i n g 10 -1 2.

T h e v a r i o u s m o d e l s o f r e a c t i v e s p u t t e r i n g c a n b e v e ri fi e d b y u s i n g t h e d a t a f r o m

e x p e r i m e n t s i n w h i c h t h e d e p o s i t i o n r a t e h a s b e e n m e a s u r e d a s a f u n c t i o n o f

d i f f er e n t p a r a m e t e r s , i n c l u d i n g t h e p a r t i a l p r e s s u r e o f r e a c t i v e g a s. T h e s e m e a s u r e -

m e n t s a r e c o m p l i c a te d b y t h e d i v er s it y o f t h e i n t e ra c t i o n s o f b o t h s p u t t e r e d a n d

a d s o r b e d p a r t i c l e s w i t h t h e s u b s t r a t e w h e r e t h e s p u t t e r e d m a t e r i a l i s d e p o s i t e d .

T h u s t h e s p u t t e r i n g y i e ld is in g e n e r a l n o t p r o p o r t i o n a l t o t h e d e p o s i t i o n r a t e 13.

A d e c r e a s e in t h e d e p o s i t i o n r a t e a s t h e p a r t i a l p r e s s u r e o f th e r e a c t i v e g a s is

i n c r e a s e d h a s b e e n c o r r e l a t e d b y v a r i o u s a u t h o r s w i t h a d e c r e a s e i n s p u t t e r i n g

r a t e 6 '1 '1 2 , w i t h p l a s m a c h a r a c t e r i s t ic s 14 a n d w i t h d i f f er e n t p h y s i c o c h e m i c a l

p r o c e s s e s o n t h e s u b s t r a t e 15.

D u r i n g t h e la s t f if te e n y e a r s a l a rg e n u m b e r o f e x p e r i m e n t a l d a t a h a v e b e e n

p u b l i sh e d , a n d m a n y m o d e l s o f r e a c ti v e sp u t t e r i n g h a v e b e e n c o n s t r u c t e d . A l l th e s e

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186 J. HRBEK

m o d e l s c a n b e c la s si fi ed a c c o r d i n g t o t h e p o s i t io n a t w h i c h t h e in t e r a c t i o n b e t w e e n

t h e r e a c ti v e g a s m o l e c u l e s a n d t h e ta r g e t a t o m s t a k e s p l a ce , e g o n t h e t a r g e t , i n t h e

p l a s m a o r a t t h e s u b s t r a t e 16.

U n d e r c e r t a in e x p e r i m e n t a l c o n d i t i o n s t h e t a r g e t s u rf a c e c a n b e c o n s i d e r e d a s

t h e m o s t p r o b a b l e i n t e r a c t i o n s it e 17. F o r t h is s it e, o x i d a t i o n l , g e t t e r i n g 11 a n d

a d s o r p t i o n 12 w e r e s u g g e s t e d a s th e m e c h a n i s m s r e s p o n s i b l e f o r r e a c ti v e s p u t t e r in g .

I n t h e se p a p e r s t h e a u t h o r s s t u d i e d t h e c h a n g e s i n d e p o s i t i o n r a t e a s a f u n c t i o n o f

t he p a r ti a l p r e s s ur e a n d o f o t h e r p a r a m e t e r s m e a s u r e d s i m u l t a n e o u s ly , e g t h e m a s s

s p e c t r u m o f th e p a r t ic l e s s p u t t e r e d f r o m t h e s u r f a c e 1~ o r t h e d i s c h a r g e c h a r a c t e r i s -

t i c s ~o.

0 . 5

m

k

[ro,]

1 . 0

v 0 0

o I I I I

1 5 1 6 1 7 1 8

1 0 1 0 1 0 1 0

z o 2 1 [0 ~ - 2 ~ ~ ]

F i g . 1 . T h e r e l a t i v e s p u t t e r i n g y i e l d k a s a f u n c t i o n o f t h e i m p i n g i n g r a t e Z ( c m 2 s ~) o f th e r e a c t i v e g a s .

T h e T i O 2 t a rg e t g a s c o m b i n a t i o n w a s m e a s u r e d a t p r i m a r y i o n c u r r e n t d e n s i t ie s o f 2 5 0 p A c m 2 ( O )

a n d 3 0 p A c m -2 ( ) .

z I N 2 [ o - 2 - I ]

1 5 1 6 1 7 1 8

1 0 1 0 1 0 1 0

k

[ , e , ] l l l l

1 . 0 - -

0 . 5 - -

o

1 5 1 6 1 7 1 0 1 8

1 0 1 0 1 0

F i g . 2. T h e e x p e r i m e n t a l v a l u e s o f t h e r e l a t iv e s p u t t e r i n g y i e l d k a s a f u n c t i o n o f th e i m p i n g i n g r a te Z o f

t h e re a c t i v e g a s f o r M o - O 2 ( 0 ) a n d M o N 2 ( C) ) t a r g e t - g a s c o m b i n a t i o n s . T h e p r i m a r y i o n c u rr e n t

d e n s i t y w a s 1 5 0 l a A c m - 2

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S P U T T E R I N G O F M E T A L S I N T H E P R E S E N C E O F R E A C T I V E G A S E S 1 8 7

I n th e p r e s e n t w o r k t h e sp u t t e r i n g y ie ld s o f T a , T i, M o a n d W w e r e m e a s u r e d a s

a f u n c t i o n o f th e p a r t i a l p r e s s u r e o f r e a c t i v e g a s ( 0 2 , N 2 ) , a n d t h e e x p e r i m e n t a l d a t a

a r e e x p la i n e d i n te r m s o f a n a d s o r p t i o n m o d e l .

2 . E X P E R I M E N T A L

T h e e x p e r i m e n t s w e r e c a r r i e d o u t i n a n a l l - g l a s s h i g h v a c u u m a p p a r a t u s

e v a c u a t e d b y o il d i ff u si o n a n d t i t a n i u m s u b l i m a t i o n p u m p s t o a n u l t im a t e p r e s s u r e

o f l es s t h a n 1 0 - s P a . T h e r e s i d u a l g a s , c o n s i s t i n g m a i n l y o f C O , N 2 a n d H 2 0 , w a s

c h e c k e d w i t h a C e n t r o n i c A I G 5 0 a n a l y t i c a l i o n g a u g e . T h e s p u t t e r i n g y i e l d s w e r e

c a l c u la t e d f r o m t h e w e ig h t lo s se s o f th e m e t a l t a r g e ts c a u s e d b y b o m b a r d m e n t w i th

A r i o n s o f e n e r g y 2 . 3 k e V . T h e i o n s o u r c e w i t h o s c i l l a ti n g e l e c t ro n s a n d i o n

e x t r a c t i o n p e r p e n d i c u l a r t o t h e e l e c tr o n b e a m a x i s w a s b u i l t a c c o r d i n g t o t h e d e s ig n

o f K o e d a m 18. S e c o n d a r y e l e c t r o n e m i s si o n f r o m t h e t a r g e t w a s s u p p r e s s e d b y a

c o m b i n a t i o n o f m a g n e t i c a n d e l e c tr o s t at ic f ie ld s. T h e w e i g h t l o ss e s w e r e m e a s u r e d

u s i n g a q u a r t z s p r i n g b a l a n c e w i t h a s e n s i ti v i ty o f 0 . 00 5 m g . T h e t a r g e t s w e r e

t r a n s f e r r e d m a g n e t i c a l ly in v cuo f r o m t h e ta r g e t c h a m b e r t o t h e b a l a n c e o r t o t h e

h e a t i n g c ell f o r o u t g a s s in g b y e le c t ro n b o m b a r d m e n t .

T h e p u r i t y o f t h e r e a c ti v e g a se s u s e d i n t hi s s t u d y w a s c h e c k e d w i t h a n A I G 5 0.

T h e a r g o n u s e d a s th e i n e rt g a s f o r s p u t t e r i n g w a s s p e c t r o s c o p i c a l ly p u r e . T h e m e t a l

t a r g e t s w e r e 0 . 2 - 0 . 5 m m s h e e t s o f 9 9 . 7 ~ o T i , 9 9 . 9 ~o M o , 9 9 . 9 9 /o T a a n d 9 9 . 9 8 /o W .

T h e s t a n d a r d d e v i a t io n o f t h e m e a s u r e d s p u t t e r i n g y i el ds w a s 13 ~ .

k

[ r e ]

1.0

0.5

15 16 17 18

10 10 10 10

o I I 1 I

~5 16 1017 1018

10 10

Z O 2 ) [cm-2 s 1 ]

F i g . 3. T h e e x p e r i m e n t a l v a lu e s o f k a s a f u n c t i o n o f Z f o r t h e T a 0 2 0 ) a n d T a - N 2 O ) t a r g e t - g a s

c o m b i n a t i o n s . T h e p r i m a r y i o n c u r r e n t d e n s i t y w a s 1 5 0 l aA c m - z .

3. RESULTS

T h e r e l a t i v e s p u t t e r i n g y i e ld s k ( t h e r a t io o f t h e y i e ld i n th e p r e s e n c e o f th e

r e a c t i v e g a s to t h a t i n t h e a b s e n c e o f t h e r e a c t iv e g a s ) a s a f u n c t i o n o f t h e i m p i n g i n g

r a t e Z o f t h e re a c t i v e g a s m o l e c u l e s a r e p l o t t e d i n F i g s . 1 - 4 . T h e i n f lu e n c e o f t h e

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188 J. HRBEK

k

[ e ]

1.0

0 . 5

Z N 2) ~ m - 2 ~ ]

1 5 1 6 1 7 1 8

1 0 1 0 1 0 1 0

I I I

o I I 1 I

15 16 17 18

1 0 1 0 1 0 1 0

Z O 2 ) ~ m - 2 ~ 1]

F i g. 4 . T h e e x p e r i m e n t a l v a l u e s o f k a s a f u n c t i o n o f Z f o r t h e W 0 2 ( 0 ) a n d W N 2 ( C ) ) t a r g e t g a s

com binations. The ~rimaryion current density was 150 ~A cm 2.

o x y g e n i m p i n g i n g r a t e o n t h e T i s p u t t e r i n g y i e ld f o r p r i m a r y i o n c u r r e n t d e n s it ie s o f

2 5 0 la A c m - 2 a n d 3 0 ~ tA c m 2 is s h o w n i n F i g . I . F i g u r e s 2 , 3 a n d 4 s h o w k rersus

p l o t s f o r M o O 2 a n d M o N 2 t a r g e t g a s c o m b i n a t i o n s , T a O 2 a n d T a N 2

t a rg e t g as c o m b i n a t i o n s a n d W 0 2 a n d W N 2 t a rg e t ga s c o m b i n a t i o n s r e-

s p e c t i v e l y .

I n a ll t a r g e t g a s c o m b i n a t i o n s t h e s p u t t e r i n g y i el d w a s f o u n d t o d e c r e a s e t o

a b o u t 0 . 4 0 .1 o f t h e in i ti a l v a l u e . A l l t h e c u r v e s h a v e a s i g m o i d a l s h a p e w i t h a n

i n f le c t io n p o i n t t h a t s h i ft s t o h ig h e r p r e s s u r e s w h e n t h e p r i m a r y i o n c u r r e n t d e n s i t y

is i n c r e a s e d .

4. DISCUSSION

W i t h a p p r o p r i a t e p r e s s u r e a n d t e m p e r a t u r e c o n d i t i o n s t h e r e a c ti v e g a s c a n b e

c h e m i s o r b e d o n t o t h e m e t a l s u r f a c e . I f a ta r g e t s u r f a c e t h a t i s c o v e r e d w i t h a

c h e m i s o r b e d l a y e r is b o m b a r d e d b y io n s , t h e a d s o r b e d p a r t ic l e s w ill b e r e m o v e d

f r o m t h e s u r fa c e n o t o n l y b y d e s o r p t i o n b u t a l s o b y s p u t t e r in g .

T h e s p u t t e r e d p a r ti c le s o r i g i n a t e b o t h f r o m t h e s u r f a c e a n d f r o m t h e b u l k o f t h e

t a rg e t . M o s t p a r t ic l e s a r e s p u t t e r e d f r o m a v e r y th i n s u r f a c e l a y e r ~0 . I t is e v i d e n t t h a t

w i t h a n i n c re a s i n g s u r f a c e c o v e r a g e o f c h e m i s o r b e d g a s t h e p r o b a b i l i t y t h a t t h e

a d s o r b e d p a r t i c l e s w il l b e s p u t t e r e d w i ll a l s o i n c r e a s e 2 a n d s i m u l t a n e o u s l y t h e

s p u t t e r i n g o f m e t a l p a r t ic l e s f r o m t h e s u rf a c e w i ll b e r e d u c e d . T h u s t h e s p u t t e r i n g

y i el d o f g a s - c o v e r e d m e t a l s h o u l d b e l o w e r t h a n t h e y ie l d o f th e c l ea n m e t a l b e c a u s e

p a r t o f th e p r i m a r y i o n e n e r g y w ill b e u s e d f o r s p u t t e r i n g t h e a d s o r b e d l a y e r. I f t h is is

s o , w e m i g h t e x p e c t t h e m e t a l s p u t t e r i n g y i e ld t o d e p e n d o n t h e s u r f a c e c o v e r a g e , a s

s h o w n i n F i g . 5 .

L e t us s u p p o s e t h a t t h e a d s o r p t i o n is g o v e r n e d b y th e L a n g m u i r i s o t h e r m .

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SPUTTERING OF METALS IN THE PRESENCE OF REACTIVE GASES 189

e - o o < e < l o = 1

Fig. 5. Two contributions to the sputtering yield can be distinguished: the surface contribution Fs and

the bulk contribution Fa, When the coverage O of the metal surface ncreases, Fs is reduced and adsorbed

particles are also sputtered from the surface contribution Fsa).

Using this appro xim at ion we can write 21

s Z l - O ) = F A O 1)

where s is the sticking probability, Z the imping ing rate cm - z s- 1) of gas molecules

on the surface, O the surface coverage and FA the rate cm -2 s -1) of removal of

adso rbed particles from the surface.

If the actual sputtering rate Fe is a linear combinati on of the sputtering rates F1

a t O = l a n d F o a t O = 0 w e o b t a i n

F o = r o - r o - r O 0

2)

Using

F I / F o = m

and

F o / F o = k

and rear rangin g eqn. 2) we can write

1 - k

O = - - 3)

1 - m

By subst itut ion ofe qn . 3) into eqn. 1) we get

s Z

k = 1 s Z + F g 1 - m ) 4)

This equation can readily be compared with the experimental data. The sputtering

yield and the sputtering rate are proportional so that the normalized sputtering

rates k and m can be determined from the measured sputtering yields together with

the values s Z . The value of the removal rate FA is determined from the condition

tha t k = m + 1) because then F A = s Z .

As an example, the Ti-O 2 targe t-gas com bina tio n results are plotted together

with the model curve in Fig. 6. The experimental data for the W -O z and W - N z

target-gas combinations could be fitted reasonably well also. The decrease in

sputtering yield for the Ta - O / a n d Mo -N 2 systems is steeper than predicted by eqn.

4). In contrast , for the Ta N z and Mo -O 2 systems the inflection regions of the

experimental curves are elongated in compar iso n with the model curve.

The assumptio ns used for the derivation ofeqn. 1) are not completely fulfilled

in the sputtering process. In the course of the experiment the target is heated owing

to the ion bombardment; furthermore, when the impinging rate of oxygen or

nitrogen on the target is high, the surface coverage can be greater than unity. One o f

the assumptions we made was that the surface was homogeneous with respect to

adsorpt ion but this can be made invalid by ion bomb ar dme nt 22. In spite of evident

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190 J. HRBEK

k

[ e ]

1.0

0.5 m

0 I I 1

1 5 1 6 1 7 1 81 0 1 0 1 0 1 0

Z O 2 ) [ c m - 2 s 11

Fig. 6. The calculated k =./ (Z ) curves (eqn. (4)) com pared with the experimen tal data for the Ti O z

target--gas com bination : - , mo del: O, 250 gA cm a ; , 30 A cm - 2.

v i o l a t i o n o f t h e a s s u m p t i o n s u s e d in t h e d e r i v a t i o n o f e qn . ( 1 ), t hi s a p p r o x i m a t i o n is

w i d e l y u s e d i n t he s u r f a c e a p p l i c a t i o n s o f s e c o n d a r y i o n m a s s s p e c t r o s c o p y 23, 2,,

T h e s p u t t e r i n g y i el d o f a d s o r b e d g a s w ill c e r t a i n l y b e a f u n c t i o n o f c o v e r a g e .

D e p e n d i n g o n t h e a c t u al m e c h a n i s m o f a d s o r p t i o n a n d s p u t t e r i n g w e e x p e ct t h a t

w h e n g a s is a d s o r b e d a n d s p u t t e r e d i n a t o m i c f o r m t h e s p u t t e r in g y i el d o f th e

a d s o r b e d g a s will be p r o p o r t i o n a l t o th e c o v e r a g e , w h e r e a s f o r a t o m i c a d s o r p t i o n

a n d m o l e c u l a r s p u t t e r i n g t h e y i el d w ill b e p r o p o r t i o n a l t o th e s e c o n d p o w e r o f t h e

c o v e r a g e . F o r t h e l a tt e r m e c h a n i s m w e s h a ll c h a n g e t h e a s s u m p t i o n o f a l i n ea r

c o m b i n a t i o n ( e q n . ( 2 ) ) t o

f o = F o- f o - f t ) O (5 )

a n d t h u s

I s Z \

k = 1 - [ s Z - + Z ] ( 1 - m ) (6)

T h i s e q u a t i o n is a b et te r a p p r o x i m a t i o n t h a n e q n . ( 4) f o r t he M o - O 2 a n d T a - N 2

t a r g e t g a s c o m b i n a t i o n s .

F r o m s p u t t e r i n g t h e o r y i t f o l l o w s t h a t th e s p u t t e r e d p a r ti c le s o r i g i n a t i n g f r o m

t h e b u l k a r e c h a r a c t e r i z e d b y a h i g h e r k i n e t i c e n e r g y t h a n t h e p a r ti c le s f r o m t h e

s u r f a c e r e g i o n 19. W e m a y t h u s e x p e c t t h a t f o r t h e c o v e r e d s u r f a c e t h e r e w i ll a l s o b e

c h a n g e s i n t h e e n e r g y d i s t r i b u t i o n o f t h e s p u t t e r e d m e t a l p a r t ic l es . T h e m a x i m u m i n

t h e e n e r g y d i s t r i b u t i o n s h o u l d b e s h i f te d t o h i g h e r e n e r g y v a l u e s b e c a u s e t h e

n u m b e r o f m e t a l p a r ti c le s o r i g i n a t i n g a t th e s u r f a c e is r e d u c e d . S o f ar , h o w e v e r ,

t h e r e a r e n o d i r e c t e x p e r i m e n t a l d a t a c o n f i r m i n g t h i s c o n c l u s i o n , b u t i n d i r e c t

i n f o r m a t i o n c o n c e r n i n g t he e n e r g y sp e c t r a o f s p u t t er e d i o n s s u p p o r t s t h e pr e-

d i c t i o n 2 s .

T h e a s s u m p t i o n t h a t w e h a v e u s e d c o n c e r n i n g t h e c o m b i n a t i o n o f s p u t t e r in g

r a t e s h a s b e e n u s e d a l s o i n o t h e r m o d e l s o f t h e r e a c t i v e s p u t t e r i n g p r o c e s s 1 ~ 2.

7/26/2019 1977 TSF Sputt

7/7

SPUTTERING OF METALS IN THE PRESENCE OF REACTIVE GASES 191

B e c a u s e t h e r e a r e s o m a n y o t h e r a p p r o x i m a t i o n s t h e r e i s n o p o s s i b i l i t y o f

c o m p a r i s o n w i t h t h e e x p e r im e n t a l d a t a m e a s u r e d b y o t h e r a u t h o r s

5. CONCLUSION

T h e i n f lu e n c e t h a t t h e p a r t i a l p r e s s u r e o f t h e r e a c t i v e g a s e x e r t s o n m e t a l

s p u t te r i n g y ie ld s w a s m e a s u r e d a n d w a s i n te r p r e te d b y m e a n s o f th e L a n g m u i r

i s o t h e r m u s i n g th e a s s u m p t i o n t h a t t h e a c t u a l s p u t t e r i n g y ie l ds c a n b e e x p r e ss e d a s a

l i n e a r c o m b i n a t i o n o f th e s p u t t e r i n g y i e l d o f t h e c l e a n t a r g e t a n d t h e s p u t t e r i n g y i e l d

o f t h e ta r g e t c o v e r e d w i t h a n a d s o r b e d l a y e r. D i r e c t m e a s u r e m e n t o f t h e s p u t t e r i n g

y i e l d s o f t h e m e t a l e n a b l e d u s t o e x c l u d e u n c e r t a i n t i e s a b o u t t h e n a t u r e o f t h e

i n t e r a c t i o n o f t h e s u b s t r a t e w i t h t h e i n c o m i n g p a r ti c le s .

T h e r e a c ti v e s p u t te r i n g m e c h a n i s m i s c o n t r o l l e d s i m u l t a n e o u s l y b y t h e

a d s o r p t i o n - s p u t t e r i n g m e c h a n i s m o f th e re a c t iv e g a s a d s o r b e d , b y c h a n g e s in th e

s u r f a c e b i n d i n g e n e r g y d u e t o a d s o r p t i o n a n d f i n a ll y b y c o l li s io n m e c h a n i c s .

ACKNOWLEDGMENTS

T h e a u t h o r g r a t e f u l l y a c k n o w l e d g e s th e h e l p f u l c o m m e n t s m a d e b y D r s . (~.

J e c h a n d Z . K n o r .

REFERENCES

1 C.J. Corbek, J. Opt . Soc . Am. , 23 1933) 109.

2 H. Koenig and L. Heisinger,

Festschr i f t Hereaus Plat inschmelze ,

Hereaus Platinschmelze, Hanau,

1947, p. 202.

3 G. K. Wehner,

Phys. Rev. , 108

1957) 35.

4 O.C . Yonts and D. E. Harrison, J. Appl . Phys. , 31 1960) 1583.

5 R.E. Jones, H. F. Winters and L. I. Maissel,

J. Vac. Sci. Technol.,

5 1967) 84.

6 E. Hollands and D. S. Campbell, J . Mater . Sc i . , 3 1968) 544.

7 H. F. Winters,

J. Vac. Sci. Technol., 8

1971) 17.

8 M. Cantagrel and M. Marchal,

J . Ma ter . Sc i . , 8

1973) 1711.

9 M. Bernheim and G. Slodzian, In t . J. Mas s Spec trom. Ion Phys . , 12 1973) 93.

10 J. Heller, Thin S olid Films, 17 1973) 163.

11

F . S h i n o k i a n d A . I t o h , J . A p p l . P h y s . ~ 4 6 1 9 7 5 ) 3 3 8 1 .

12 T. Abe and T. Yamashina, Thin Solid Films, 30 1975) 19.

13 R.E. Jones, C. L. Standley and L. I. Maissel, J . Appl . Phys . , 38 1967) 4656.

14 J.B. Llounsburry, J. Vac. Sci. Technol., 6 1969) 838.

15 H. F. Winters, D. L. Raimondi and D. E. Horne, J . Appl . Phys . , 40 1969) 2996.

16 L. Holland and G. Siddall, Vacuum, 4 1953) 375.

17 L. I. Maissel, in L. I. Maissel and R. Glang eds.),

Handbook o f Thin Fi lm Technology ,

McGraw-

Hill, New York, 1970, Chap. 4.

18 M. Koedam,

Ph il ips Res. Rep. , 16

1961) 101.

19 P. Sigmund,

Phys . Rev . , 184

1969) 383.

20 H. F. Winters and P. Sigmund, J . Appl . Phys . , 45 1974) 4760.

21 D.O. Hayward and B. M. W. Trapnell, Chemisorption, 2nd edn., Butterworths, London, 1964.

22 R. S. Gvosdover, V. M. Efremenkova, L. B. Shelyakin and V. E. Yurasova, Radiat . Ef fec t s , 27

1976) 237.

23 A. Benninghoven,

Sur f . Sc i . , 35

1973) 427.

24 G. Blaise and M. Bernheim, Surf . Sci . , 47 1975) 324.

25 T. Ishitani, H. Tamura and T. Shinmiyo,

Surf . Sci . , 55

1976) 179.