Low temperature aluminum oxide deposition using trimethylaluminum

Journal o f Electronic Materials, VoL 12, No. 3, 1983

LOW TEMPERATURE ALUMINUM OXIDE DEPOSITION

USING TRIMETffILALUMINUM

R.S . E h l e , B . J . B a l i g a , and W. Katz

Genera l E l e c t r i c Company Corpo ra t e Resea rch and Development Cente r

S c h e n e c t a d y , NY 12345

(Received September 30, 1982)

A b s t r a c t

Aluminum oxide f i l m s (amorphous and 7-A1203) have been d e p o s i t e d by the o x i d a t i o n of t r i m e t h y l a l u m i n u m . P r o c e s s p a r a m e t e r s have been e v a l u a t e d and o p t i m i z e d t o o b t a i n r e a s o n a b l e growth r a t e s and f i l m p r o p e r t i e s f o r d e p o s i t i o n t e m p e r a t u r e s between 300 and 400-C. Values of the d i e l e c t r i c c o n s t a n t (7 .5 - 7 . 8 ) , the d i e l e c t r i c s t r e n g t h (7 .5 - 7 .9 X 10 v V/cm), the iq~ex of r e f r a c t i o n (1 .54 - 1 . 6 7 ) , and the r e s i s t i v i t y (> 10 "~ ohm--cm) compare f a v o r a b l y wi th AI_O_ f i l m s grown wi th o t h e r p r o c e s s e s a t h i g h e r z d e p o s i t i o n t e m p e r a t u r e s . Fi lm a n a l y s i s by s e c o n d a r y ion mass s p e c t r o m e t r y i d e n t i f i e d a d i s t r i b u t i o n of ca rbon and sodium i m p u r i t i e s .

Key Words: aluminum ox ide , chemica l vapor d e p o s i t i o n , low t e m p e r a t u r e .

587

0361-5235/83/1203 58753.00 �9 1983 A[ME

588 Ehle, Bsdiga and Kstz

I n t r o d u c t i o n

Aluminum oxide f i l m s have been employed in s e m i c o n d u c t o r d e v i c e a p p l i c a t i o n s as I n t c r m c t a l d i e l e c t r l c s f o r s i l i c o n i n t e g r a t e d c i r c u i t s , p a s s i v a t i o n d l e l c c t r l c s f o r GaAs, and d i e l e c t r i c s f o r GaAs MIS s t r u c t u r e s w i th r e p o r t e d i n v e r s i o n a t the i n t e r f a c e ( I ) . The chemlca l vapor d e p o s i t i o n (CVD) t e c h n i q u e s which have been deve loped f o r d e p o s i t i o n have i n c l u d e d the r e a c t i o n o f t r l m c t h y l a l u m i n n m (TMA1) wi th n i t r o u s oxide ( 2 ) , the gas phase h y d r o l y s i s o f AIC1. wi th a m i x t u r e of H 2 and CO (3) the p y r o l y t i c d e c o m p o s i t i o n o f aluminum a l~ox ide (4~, and ' the o x i d a t i o n o f TMA1 ( 5 ) . D e t a i l s o f the p h y s i c a l and chemica l p r o c e s s e s and the f i l m p r o p e r t i e s have been r e p o r t e d in t h e s e p u b l i c a t i o n s f o r d e p o s i t i o n t e m p e r a t u r e s in e x c e s s o f 400~ However, the l i t e r a t u r e c o n t a i n s l e s s d e t a i l e d i n f o r m a t i o n p e r t a i n i n g t o the d e p o s i t i o n o f f i l m s a t t e m p e r a t u r e s below 400~

In the p r e s e n t work we have d e p o s i t e d A1203 f i l m s by the o x i d a t i o n o f TMAI in an a rgon a tmosphe re . The p r o c e s s i s s i m i l a r to t h a t r e p o r t e d by l )uffy and Kern ( 5 ) . The scope of our i n v e s t i g a t i o n was l i m i t e d by the t e c h n o l o g i c a l r e q u i r e m e n t s o f a program which n e c e s s i t a t e d the low t e m p e r a t u r e d e p o s i t i o n o f At.O_ on GaAs. A c c o r d i n g l y we

z have i n v e s t i g a t e d p r o c e s s p a r a m e t e r s e f f e c t l n g the d e p o s i t i o n a t t e m p e r a t u r e s between 300~ and 400oC. Fi lm p r o p e r t i e s i n c l u d i n g the index of r e f r a c t i o n , the d i e l e c t r i c c o n s t a n t , the d i e l e c t r i c s t r e n g t h , the s t r u c t u r e , the r e s i s t i v i t y , and the i m p u r i t y c o n t e n t and d i s t r i b u t i o n have been d e t e r m i n e d .

Expe r imen t a l

A schemat i c o f the CVI) a p p a r a t u s employed d u r i n g the s t u d y i s shown in F i g u r e i and i s b a s i c a l l y a v e r t i c a l open tube system wi th the gas f low p e r p e n d i c u l a r to the s u b s t r a t e . The 0 .05 ohm-am p - t y p e s i l l c o n s u b s t r a t e s used were s u p p o r t e d by a 7 .6 ca d i a m e t e r g r a p h i t e r e s i s t a n c e h e a t e r housed in a 15 cm d i a m e t e r 30 cm h igh b e l l j a r . The TNAI was i n t r o d u c e d i n t o the r e a c t i o n chamber wi th an a rgon a s s i s t c a r r i e r gas by p a s s i n g a rgon t h r o u g h the TNA1 c o n t a i n e r which was h e l d a t a c o n s t a n t t e m p e r a t u r e of 20~ Th is m i x t u r e was coup led t o the main a rgon f low which e n t e r e d the r e a c t i o n chamber t h rough a funne l employed t o

Low Temperature Aluminum Oxide Deposition

02 ~ F L O W CONTROLLER

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F i g u r e 1 : CVD a p p a r a t u s o f d e p o s i t i o n o f AI203 b y t h e o x i d a t i o n o f t r i m e t h y l a l u m i n u m .

mix t h e r e a c t a n t g a s e s a t t h e s u r f a c e o f t h e s u b s t r a t e and m i n i m i z e c o m p e t i n g g a s p h a s e r e a c t i o n s w h i c h one m i g h t e x p e c t w i t h a more h o m o g e n e o u s m i x t u r e w i t h i n t h e r e a c t i o n c h a m b e r . The o x y g e n was i n t r o d u c e d i n t o t h e r e a c t i o n c h a m b e r t h r o u g h a s e p a r a t e l i n e l o c a t e d a t t h e s i d e o f t h e b e l l j a r b e t w e e n t h e o u t p u t o f t h e f u n n e l and t h e t o p o f t h e s u b s t r a t e h e a t e r . The r e a c t i o n c h a m b e r was f l u s h e d w i t h a r g o n f o r t h i r t y m i n u t e s a f t e r s u b s t r a t e l o a d i n g p r i o r t o e a c h d e p o s i t i o n . A f t e r t h e s u b s t r a t e was h e a t e d t o t h e d e s i r e d d e p o s i t i o n t e m p e r a t u r e t h e a r g o n f l o w t h r o u g h t h e TMA1 b u b b l e r [TMAI(Ar ) ] was s t a r t e d t h i r t y s e c o n d s p r i o r t o i n t r o d u c t i o n o f t h e o x y g e n . The g r o w t h r a t e s we re c a l c u l a t e d a s s u m i n g t h a t g r o w t h was i n i t i a t e d a t t h e p o i n t when o x y g e n was i n t r o d u c e d .

590 Ehle, Baliga and Katz

P r o c e s s p a r a m e t e r s w h i c h w e r e h e l d c o n s t a n t t h r o u g h o u t t h e e x p e r i m e n t s w e r e t h e m a i n a r g o n f l o w r a t e ( 1 . 4 I / m l n ) , t h e a r g o n a s s i s t f l o w r a t e (80 c c / m l n ) and t h e d i s t a n c e b e t w e e n t h e f u n n e l o u t l e t and t h e s u b s t r a t e s u r f a c e (5 cm) . T h i s f u n n e l h e i g h t was i n i t i a l l y d e t e r m i n e d b y a d j u s t m e n t w h i c h p r o v i d e d u n i f o r m c l r c u l a r g r o w t h a p p r o x i m a t e l y 4 . 6 cm i n d i a m e t e r w i t h TMAI(Ar) and o x y g e n f l o w r a t e s o f 20 c c / m l n and 50 c c / m i n , r e s p e c t i v e l y , and a s u b s t r a t e t e m p e r a t u r e o f 370~ G i v e n t h e f i x e d c o n d i t i o n s m e n t i o n e d a b o v e , t h e p a r a m e t e r s w h i c h e f f e c t t h e c h e m i c a l r e a c t i o n d u r i n g d e p o s i t i o n a r e t h e c o n c e n t r a t i o n s o f o x y g e n and TMAI, and t h e t e m p e r a t u r e o f t h e s u b s t r a t e . The o x y g e n and TMAI(Ar) f l o w r a t e s w e r e v a r i e d f rom $ t o 140 c c / m i n and 1 . 8 t o 50 c c / m l n r e s p e c t i v e l y , and d e p o s i t i o n t e m p e r a t u r e s r a n g e d b e t w e e n 300 and 4 0 0 - C .

The t h i c k n e s s and i n d e x o f r e f r a c t i o n w e r e m e a s u r e d w i t h a R u d o l p h a u t o EL I I e l l i p s o m e t e r (~ = 6328 ~) and n o r m a l l y e x h i b i t e d u n i f o r m i t i e s o f 10& and 1 5 , r e s p e c t i v e l ~ . The f i l m t h i c k n e s s was n o r m a l l y b e t w e e n 1500 and 2000 A. Aluminum d o t s 0 . 2 5 mm i n d i a m e t e r we re e v a p o r a t e d on t h e f i l m s and a u n i f o r m A1 e v a p o r a t i o n was c o m p l e t e d on t h e r e v e r s e s i d e o f t h e s u b s t r a t e t o fo rm MOS s t r u c t u r e s . The d i e l e c t r i c s t r e n g t h and c a p a c i t a n c e w e r e m e a s u r e d w i t h t h e s e u n i t s . The d i e l e c t r i c c o n s t a n t was c a l c u l a t e d f rom t h e c a p a c i t a n c e and f i l m t h i c k n e s s .

F i l m s t r u c t u r e was e v a l u a t e d u s i n g t r a n s m i s s i o n e l e c t r o n m i c r o s c o p y (TEM) and low a n g l e X - r a y d i f f r a c t i o n . I m p u r i t i e s p r e s e n t and t h e i r d i s t r i b u t i o n w i t h i n t h e f i l m s w e r e d e t e r m i n e d u s i n g s e c o n d a r y i o n mass s p e c t r o m e t r y (SIMS).

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D e p o s i t i o n R a t e

The c h e m i c a l r e a c t i o n d u r i n g t h e d e p o s i t i o n o f A1203 b y t h e o x i d a t i o n o f TMA1 m i g h t be e x p e c t e d t o p r o c e e d a s

2(C!t3) 3 A1 + 1202 --.-) A1203 + 6C02 + 9IL20

o r

(i)

Low Temperature Aluminum Oxide Deposition 591

4(CH3) 3 AI + 1502 -9 2A1203 + 12CO 2 + ISB I (2)

E i t h e r of t h e s e e q u a t i o n s i n d i c a t e t h a t t he oxygen t o TMAI mole r a t i o must be l a r g e t o o b t a i n c o m p l e t e o x i d a t i o n of t he TMA1. The dependence of the growth r a t e on the oxygen c o n c e n t r a t i o n a t a t e m p e r a t u r e of 350~ w i t h a TMAI(Ar) f low of 20 c c / m i n i s shown i n F i g u r e 2. As would be e x p e c t e d , t h e r e i s a r e l a t i v e l y s t r o n g dependence on the oxygen f low r a t e s i m i l a r to t h a t o b s e r v e d i n o t h e r o x i d e d e p o s i t i o n s y s t e m s ( 7 , 1 0 , 1 1 ) . Th i s i s a t t r i b u t e d t o t he i n c r e a s i n g oxygen a d s o r p t i o n on the r e a c t i o n s u r f a c e which p r o m o t e s f a s t e r r e a c t i o n . F i l m s d e p o s i t e d w i t h f low r a t e s l e s s t han 30 c c / m i n e x h i b i t e d poo r e l e c t r i c a l c h a r a c t e r i s t i c s and f o r f low r a t e s g r e a t e r t han 140 c c / m i n the d e p o s i t i o n became nonun i fo rm and i r r e p r o d u c i b l e .

4oo I .~ 300

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OXYGEN FLOW RATE (cc/min)

F i g u r e 2 : Dependence of growth r a t e on t h e oxygen f low r a t e .

592 Ehle , Ba l iga a n d Katz

E q u a t i o n s (1) and (2) p r e d i c t t h a t the oxygen c o n c e n t r a t i o n must be i n c r e a s e d by a f a c t o r of 12 and 7 . 5 , r e s p e c t i v e l y , t o doub le the A1.O. f o r m a t i o n . To a s c e r t a i n z ~ the r e a c t i o n t h a t a p p l i e s t o our d e p o s i t i o n s , a p l o t of the same growth r a t e da t a as a f u n c t i o n of the 7 . S t h and the 12 t h r o o t of the oxygen f low was made. The p l o t shown in F i g u r e 3 u s ing the 7 . S t h r o o t g i v e s a s t r a i s h t l i n e . Th i s i s good e v i d e n c e t h a t the d e p o s i t i o n p r o c e e d s a c c o r d i n g t o the chemica l r e a c t i o n p r e d i c t e d by E q u a t i o n ( 2 ) .

~ TMAi(Ar ) : 20cc/min T =550~

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~ 200 �9

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7"5t/OXYGEN FLOW RATE (cc/min)

F i s u r e 3: Growth r a t e p l o t t e d as t he 7 . S t h r o o t of oxygen f low r a t e .


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TMAJ. (Ar) : 20cc/min e ~ 2 = 50cc/min

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I 1.7 1.75

F i g u r e 4 : A r r h e n i u s p l o t of t he dependence of the growth r a t e on t h e s u b s t r a t e t e m p e r a t u r e .

An A r r h e n i u s p l o t of the 8rowth r a t e v e r s u s t e m p e r a t u r e i s shown i n F i g u r e 4 f o r g rowth t e m p e r a t u r e s be tween 300 and 400~ The a c t i v a t i o n e n e r g y d e r i v e d from the s l o p e i s 20 .5 k c a l / m o l e . At t e m p e r a t u r e s above 400~ t h e d e p o s i t i o n p r o c e s s becomes u n s t a b l e r e s u l t l n g i n nonun i f o r m f i l m s . In a d d i t i o n the growth r a t e d e c r e a s e s a t h l s h e r t e m p e r a t u r e s and becomes i r r e p r o d u e l b l e . Growth r a t e r e d u c t i o n as t he t e m p e r a t u r e i s i n c r e a s e d has been o b s e r v e d i n o t h e r CVD p r o c e s s e s ( 6 , 7 ) , and I s p r o b a b l y the r e s u l t of an i n c r e a s e i n t h e homogeneous gas phase c h e m i c a l r e a c t i o n o c c u r r i n 8 a t t he e l e v a t e d chamber t e m p e r a t u r e s . Th i s c a u s e s a d e p l e t i o n of r e a c t a n t s a t t he w a f e r s u r f a c e when the t e m p e r a t u r e in t he chamber i n c r e a s e s and r e s u l t s in a d rop i n t he growth r a t e b e c a u s e a h e t e r o g e n e o u s r e a c t i o n i s r e s p o n s i b l e f o r


f i l m growth on the w a f e r s . Our da t a shows t h a t growth r a t e s above I00 ~ pe r min can be a c h i e v e d in the s t a b l e growth r e g i o n a t t e m p e r a t u r e s below 350~ In compar i son , growth r a t e s r e s u l t i n g from AI203 d e p o s i t i o n s by the gas phase h y d r o l y s i s of AIClz ( 3 ) , and the p y r o l y t i c d e c o m p o s i t i o n o f aluminum a l k o x i d e - (4 ) a re nea r I00 ~/min a t 900~ and 70 ~/min a t 420~ r e s p e c t i v e l y . Duffy and Kern (5) o b s e r v e d growth r a t e s o f 500 ~/min a t a d e p o s i t i o n t e m p e r a t u r e of 420~

Exper iments were a l s o conduc t ed t o de t e rmine the dependence of the growth r a t e up on the TMAI(Ar) f low r a t e a t 350eC u s i n g an oxygen f low of 100 cc /min . I t was found t h a t v a r i a t i o n of the TMAI(Ar) f low r e s u l t e d in changes o f the d e p o s i t i o n a rea (wi th a un i fo rm growth r e g i o n w i t h i n t h i s a r ea ) i n s t e a d o f an e x p e c t e d change in growth r a t e w i t h un i fo rm d e p o s i t i o n . These e f f e c t s can be obse rved in F i g u r e 5, which shows p h o t o g r a p h s of the s u b s t r a t e s w i th AI~03 d e p o s i t e d u s i n g v a r i o u s f l o w s . The d e p o s i t i o n r e s u l t i n g from a f low of 1 .8 cc /min i s shown in the lower r i g h t hand c o r n e r . The a rea of d e p o s i t i o n i s l e s s than 0 .8 cm . With i n c r e a s i n g f low, p i c t u r e d in a c lockwi se d i r e c t i o n , the d e p o s i t i o n a rea and un i fo rm r e g i o n w i t h i n t h i s a r ea i n c r e a s e s u n t i l a t a f low ra t~ of 20 cc /min t h e r e i s a un i fo rm d e p o s i t i o n a rea of 16 cm . These un i fo rm d e p o s i t i o n

F i g u r e 5: P h o t o g r a p h s o f Al~Oq f i l m s d e p o s i t e d on 2 inch s u b s t r a t e s u s ing TM~I(Ar) few r a t e s o f 1 , 8 , 4 , 10 , 15 , 20 , and 50 cc /min p i c t u r e d c l o c k w i s e from lower r i g h t .


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DIAMETER (Icm/DIV)

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I0 20 30 40 TMA,(L(Ar) FLOW RATE (cc/min)

F i g u r e 6: Dependence of d e p o s i t i o n d i a m e t e r and f i l m t h i c k n e s s on t h e TNAL(Ar) f low r a t e .

c h a r a c t e r i s t i c s a r e o b s e r v e d w i t h f l ow r a t e s up t o 40 c c / m i n . Growth t h e n becomes n o n u n i f o r m when t he f l ow i s i n c r e a s e d f u r t h e r . The same phenomenon i s shown i n F i g u r e 6 where t he d i a m e t e r o f t h e u n i f o r m d e p o s i t i o n a r e a i s p l o t t e d as a f u n c t i o n of t h e TMAI(Ar) f l ow r a t e . The g e n e r a l t h i c k n e s s v a r i a t i o n s w i t h i n t h i s d i a m e t e r a r e shown f o r s e v e r a l f l ow r a t e s I n t h e i n s e r t . The a r r o w i n t h e i n s e r t shows t h e l o c a t i o n o f t h e f u n n e l . For c o n s t a n t d e p o s i t i o n t i m e s , as t h e f l o w i s i n c r e a s e d , t he t h i c k n e s s i n t h e u n i f o r m d e p o s i t i o n r e g i o n r e m a i n s c o n s t a n t and t h e d i a m e t e r i n c r e a s e s . Based upon t h e d a t a shown I n F i g u r e 4 , we b e l i e v e t h a t t he d e p o s i t i o n r a t e i n t h e u n i f o r m t h i c k n e s s r e g i o n i s k l n e t l c a l l y l i m l t e d . As t h e r e a c t a n t s f l ow t o w a r d s t h e edges o f t h e w a f e r t he TNA1 c o n c e n t r a t i o n I s

596 Ehle, BaHga and Kstz

d i l u t e d and t h e r e a c t i o n becomes mass f low c o n t r o l l e d . T h i s r e s u l t s in a r e d u c t i o n o f t he growth r a t e a s t h e p e r i m e t e r of t he d e p o s i t i o n r e g i o n i s a p p r o a c h e d . When the f low i s i n c r e a s e d , t he h i g h e r f l u x can s u p p o r t a k i n e t i c a l l y c o n t r o l l e d r e a c t i o n o v e r more of the s u b s t r a t e a r e a b e f o r e i t i s d i l u t e d t o t he l e v e l a t which the r e a c t i o n becomes mass f l ow c o n t r o l l e d . T h i s r e s u l t s i n t he o b s e r v e d i n c r e a s e i n a r e a .

F i l m P r o p e r t i e s

The s t r u c t u r a l a n a l y s e s by TEM and low a n g l e X - r a y d i f f r a c t i o n showed t h a t some f i l m s were amorphous and i n o t h e r s t h e p o l y c r y s t a l i n e Y - A1203 phase was p r e s e n t . The u phase was more p r e d o m i n a n t w l t h f i l m s d e p o s i t e d a t t he h i g h e r d e p o s i t i o n t e m p e r a t u r e p r o v i d i n g oxygen f low r a t e s d u r i n g the d e p o s i t i o n were g r e a t e r t han 30 c c / m i n . Amorphous f i l m s were e v i d e n t a t a l l d e p o s i t i o n t e m p e r a t u r e s when oxygen c o n c e n t r a t i o n s were l o w e r .

The i n d e x of r e f r a c t i o n i s p l o t t e d as a f u n c t i o n o f t e m p e r a t u r e and oxygen f low r a t e s i n F i g u r e 7 and 8 r e s p e c t i v e l y f o r 1800 and 2000 ~ t h i c k f i l m s . No t r e n d i n t h e i n d e x was o b s e r v e d w i t h t h i c k n e s s v a r i a t i o n i n t h i s r a n g e . A p r o g r e s s i v e i n c r e a s e i n t h e r e f r a c t i v e i n d e x i s o b s e r v e d w i t h i n c r e a s i n g d e p o s i t i o n t e m p e r a t u r e s . The h i g h e r i n d e x of r e f r a c t i o n w i t h i n c r e a s i n g d e p o s i t i o n t e m p e r a t u r e i s p r o b a b l y due t o a c o r r e s p o n d i n g change i n t he m i c r o s t r u c t u r e of the f i l m s from the amorphous t o t he p o l y c r y s t a l l i n e y phase which was o b s e r v e d i n t h e s t r u c t u r a l a n a l y s i s . The i n d e x i s s i g n i f i c a n t l y l ower t han t h a t r e p o r t e d f o r pu re a and y A1~O3 ( 8 , 9 ) . However , t h e i n d e x f o r f i l m s d e p o s i t e d n e a r 370 C compare v e r y f a v o r a b l y w i t h t h o s e r e p o r t e d f o r o t h e r CVD d e p o s i t i o n p r o c e s s e s . The d a t a p o i n t of Aboaf r e s u l t i n g from t h e d e p o s i t i o n of AI20 ~ by the d e c o m p o s i t i o n o f a l m a i m m t r i i s o p r o p o x i d e [AI(OC=H~)] a t 420"C (4) i s shown i n F i g u r e 7 f o r c o m p a r i s o n . ~ ~ne d e p o s i t i o n of AI20 . a t 700:C w i t h the AICI_~ - - l l o gas

w i t h a r e f r a c t i v e i n d e x (3) and Duf fy and Kern have r e p o r t e d an i n d e x o f 1 . 6 4 f o r d e p o s i t i o n t e m p e r a t u r e s be tween 450 and 475~ (5) u s i n 8 a p r o c e s s s i m i l a r t o o u r s .


x I.&J

Z 0

w

m

I - -

I.&.

(3=

1.80

1.70

m

m

b

m

m

1.60 -

1.50 300

. . ~ B U L K AI203

TMAJL (Ar) : 20cc/min 02 = 50 cc/min

ABOAF

@

U �9

[ [ [ [ [ I I [ i [ I I

350 400 DEPOSITION TEMPERATURE (%)

F i s u r e 7 : D e p e n d e n c e o f t h e i n d e x o f r e f r a c t i o n on t h e d e p o s i t i o n t e m p e r a t u r e .


TMAI(Ar) = 20cc/min 1 . 7 - T = 5 5 0 ~

~ 1.6 i - - e~

1.5 0

r ~ U_ t~J r ~

I . I ~ I I I L I 40 80 120 160

OXYGEN FLOW RATE (cc/min) Figure 8: Dependence of the index of r e f r a c t i o n on the

oxygen f l ow r a t e .

The d l e l e c t r i c c o n s t a n t , d i e l e c t r l c s t r e n g t h , and r e s i s t i v i t y of f i l m s d e p o s i t e d a t v a r i o u s t e m p e r a t u r e s and w i t h v a r i o u s oxygen c o n c e n t r a t i o n s were a l s o m e a s u r e d . No t r e n d was o b s e r v e d as a f u n c t i o n o f t h e s e p a r a m e t e r s . The v a l u e of the d i e l e c t r i c c o n s t a n t v a r i e d be tween 7.5 and 7 .8 w h i l e v a l u e s of t he d i e l e c t r i c s t r e n g t h r a n g e d from 7 .5 ~ 7 .9 X 10- V/cm and t h e r e s i s t i v i t y was g r e a t e r t han 10 ohnr-cm. As was the case w i t h the i n d e x o f r e f r a c t i o n , t h e s e r e s u l t s compare f a v o r a b l y w i t h t h o s e r e p o r t e d i n t h e l i t e r a t u r e f o r AI_O 3 f i l m s d e p o s i t e d by o t h e r t e c h n i q u e s a t z h i g h e r t e m p e r a t u r e s .


In o r d e r to i n v e s t i g a t e the i n - d e p t h d i s t r i b u t i o n of i m p u r i t i e s in the A1203, s e c o n d a r y ion mass s p e c t r o m e t r y (SIMS) was p e r f o r m e d . ATualyses were o b t a i n e d u s i n g a Cameca IHS 3 - f ion m i c r o s c o p e . ~amples were examined u s i n g a mass a n a l y z e d p r i m a r y beam of O? h a v i n g an impac t e n e r g y of 11.5 keV and m o n i t o r i n g the ~ o s i t l v e s e c o n d a r y i o n s . Charge n e u t r a l i t y was m a i n t a i n e d on the t h i c k e r f i l m s (> 2000 ~) by u s i n g an e l e c t r o n f l o o d gun. Y m p u r i t l e s p r e s e n t in the f i l m s were i n i t l a l l y i d e n t i f i e d by r e c o r d i n g mass s p e c t r a f rom m/e of I to 100. Care was t a k e n to i n s u r e t h a t the mass s p e c t r a were o n l y r e c o r d e d + in . t ~ 3 .A~203 f i l m . The i m p u r i t y s p e c i e s found were C ana Ha . In o r d e r to f o l l o w the. 2 ~ . d i s t r i b u t i o n s of C and Na _J.n the ~N2a~3 d i e l e c t r i c e + s ~ c o n d a ~ i ~ i n t e n s i t i e s o f 12C+ and 2 as w e l l a s - AI and Si , were m o n i t o r e d as a f u n c t i o n ~ ~ u t t e r i n g t i m e . T h % e d o ~ l y - c h a r g e d s e c o n d a r y ions o f

A1 (m/e = 13 .5 ) and ~ o S i ' ' (m/e = 14) were used s i n c e the i n t e n s i t i e s o f the s l n g l y - c h a r g e d s p e c i e s were too i n t e n s e f o r the e l e c t r o n i c s . A t y p i c a l in dep th p r o f i l e f o r a f i l m d e p o s i t e d a t 380~ i s shown in F i g u r e 9 . Data a r e p l o t ~ as s e c o n d a r y ion i n t e n s i t y ( c o u n t s / s e e ) v e r s ~ s dep th

10 6

10 5

~n

10 4 o

>- 10 3

I----

z 10 2 Z

2

I0 I

I0 o I I 0 800 1600

DEPTH (Angstroms)

F i g u r e 9 :

,~__28Si + +

~ 23No + 12C+

~J~ 27AI ++ I

2400

SIMS i m p u r i t y p r o f i l e f o r AI203 f i l m d e p o s i t e d a t 3800C.

600 Ehle, Balig~, and Katz

( ~ ) . A dep th s c a l e (~) was p o s s i b l e due to pos t -bombardment measurements of the s p u t t e r e d c r a t e r s u s i n g a S loan Dektak ~ r f ~ e p r o f i l o m e t e r . One n o t e s a r e l a t i v ~ y . c o n s t a n t

"A1 - s i g n a l t h r o u g h o u t the AI~O~ f i l m . The - v S i ~ s i g n a l s een in the f i l m cou ld r e s u l t - f r o m an o r g a n i c s p e c i e s , 1 4 m +

t~i2o a l s o a t nominal mass 14. The ca rbon i m p u r i t y i s q u l t ~ p r o b a b l y i n h e r e n t in the CVD p r o c e s s w i t h the source in the o r g a n o m e t a l l i c . However. the s ~ r c ~ of the Na i m p u r i t y was i n l t l a l l y l e s s o b v i o u s . The ~ONa ~ was d e t e c t e d above the background l e v e l a t the c e n t e r of the f i l m and p r o g r e s s i v e l y i n c r e a s e d as the s u r f a c e was app roached . Th i s s u g g e s t e d the p o s s i b i l i t y of a t e m p e r a t u r e dependent source which might be a i n t e g r a l p a r t of the r e a c t i o n chamber. A c c o r d i n g l y , a l l pyrex g l a s s p a r t s of the r e a c t i o n chamber were r e p l a c e d w i t h h igh p u r i t y q u a r t z . No 23Na + cou ld be d e t e c t e d in the A1203 f i l m s a f t e r t h i s change was i n t r o d u c e d .

Summary

The e f f e c t of v a r i a t i o n s in the major d e p o s i t i o n p a r a m e t e r s upon the growth r a t e the the p r o p e r t i e s of A1203 f i l m s p r e p a r e d by the o x i d a t i o n o f TNAI have been d e t e r m i n e d . The a c t i v a t i o n energ~ fo r the growth r a t e a t t e m p e r a t u r e s be tween 300 and 400"C was found t o be 20 .5 K c a l / m o l e . The f i l m s t r u c t u r e and index of r e f r a c t i o n was found to v a r y wi th b o t h the d e p o s i t i o n t e m p e r a t u r e and the 02/TNA1 mole r a t i o . F i lm p r o p e r t i e s such as the d i e l e c t r i c c o n s t a n t , d i e l e c t r i c s t r e n g t h , and r e s i s t i v i t y appear to be r e l a t i v e l y c o n s t a n t f o r the narrow range of d e p o s i t i o n t e m p e r a t u r e s i n v e s t i g a t e d . The f i l m p r o p e r t i e s compare f a v o r a b l y wi th h i g h e r t e m p e r a t u r e CVD p r o c e s s e s r e p o r t e d in the l i t e r a t u r e f o r the d e p o s i t i o n o f A1203.


R e f e r e n c e s

[1] T. I t o and Y. Saka t , S o l i d S t a t e E l e c t r o n (1974) .

1__! , 7 5 1

[2] L.H. Ha l l and W.C. R o b i n e t t e , 7. E l ec t roehem Soc, , 1624 (1971) .

[3] V . J . S i l v e s t r i , C.M. Osburn, and D.W. Ormond, E l ec t rochem S o t . , 123 , 902 (1978) .

[4] ~.A. Aboaf , 3. E l ec t rochem S o c . , 114 , 948 (1967) .

[5] M.T. Du l ly and W. Kern, RCA Review, 754 (Dec. 1970 ) .

[ 6 ]

118

7.

W. Kern and R.C. Hein, 7. E l e c t r o c h e n S o t . , 11__!7 , 562 (1970).

[7] J .R . Shea ly , B . J . B a l i g a , R . J . F i e l d , and S.K. Ghaudhi, J . E l e c t r o c h e m S o e . , 128 , 558 (1981 ) .

[8] R.C. Weast, Ed . , p . B - 8 6 , Handbook o f Chemis t ry and P h y s i c s , 50 th Ed . , The Chem. Rubber Co. , C l e v e l a n d , Ohio (1969).

[9] P.W. Leed, p . 1 5 , Ceramics , Re luho ld P u b l . , Co. , New York (1961) .

B . J . B a l l g a and S.K. Ghandhi, 7. Appl. Phys . 4_44 , 990 (1973).

B.3. B a l l g a and S.K. Ghandhl, 7. E l ec t rochem S o t . , 123 , 941 (1976) .

[ lo]

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