Pinholes in pyrolytic oxide deposited on silicon and metals
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p a s s i v a t i n g m e t a l i n t e r c o n n e c t i o n for i n t e g r a t e d c i r c u i t s , it is n e c e s s a r y to use low t e m p e r a t u r e i n s u l a t i n g f i l m s to avoid d e g r a d i n g the m e t a l - s i l i c o n ohmic contact. Low t e m p e r a t u r e p y r o l y t i c oxide dep o s i t e d by the oxidation of s i l a n e a p p e a r s a t t r a c t i v e for m e t a l p a s s i v a t i o n b e c a u s e of its e x c e l l e n t s u r f a c e c o n f o r m i t y (edge coverage), high etch r a t e (ease in v i a hole etch), and above a l l low cost. The pinhole d e n s i t y in low t e m p e r a t u r e pyrolytic oxide f i l m s dep o s i t e d on s i l i c o n and m e t a l s was i n v e s t i g a t e d . I) E X P E R I M E N T A L PROCEDURES Oxidized c h e m i c a l - m e c h a n i c a l 1 p o l i s h e d s i l i c o n w a f e r s were used as the s u b s t r a t e for m e t a l l i z a t i o n . A l u m i n u m and m o l y b d e n u m were the m e t a l s used for this i n v e s t i g a t i o n . A l u m i n u m f i l m s were e v a p o r a t e d at about 200~ and the m o l y b d e n u m f i l m s were c h e m ically deposited by the r e d u c t i o n of m o l y b d e n u m p e n e t a c h l o r i d e at about 550~ The s i l i c o n dioxide f i l m s were deposited by the oxidation of s i l a n e at t e m p e r a t u r e s b e t w e e n 400 ~ and 500~ as has been r e p o r t e d p r e v i o u s l y . 2 B r i e f l y , the deposition was made in a h o r i z o n t a l r e a c t o r . Subs t r a t e s were heated by r f power coupled with a graphite s u s c e p t o r which was coated with s i l i c o n c a r b i d e . High p u r i t y oxygen was used a s the oxidizing agent and hydrogen a s the c a r r i e r gas. The oxygen to s i l a n e mole r a t i o was 30 to 1, and the hydrogen flow r a t e was about 30 l i t e r s per m i n . The deposition r a t e was c o n t r o l l e d by the s i l a n e and oxygen feeding r a t e . P i n h o l e d e n s i t y in oxide f i l m s deposited in s i l i c o n was d e t e r m i n e d by e l e c t r o p h o r e t i c d e c o r a t i o n . 3 E l e c t r o p h o r e t i c d e c o r a t i o n was made with acetone e l e c t r o l y t e and a copper e l e c t r o d e . The dc b i a s was 50 v which was m a i n t a i n e d for 30 m i n . P i n h o l e dens i t i e s in pyrolytic oxide f i l m s d e p o s i t e d on m e t a l s were d e t e r m i n e d by counting the c o r r o s i o n spots developed in m e t a l s d u r i n g t h e i r i m m e r s i o n in a p p r o p r i ate e t c h a n t s . Hot HC1 (48 pct) solution at 40~ was used a s etchant for a l u m i n u m s a m p l e s and hot w a t e r at 85~ for m o l y b d e n u m . The i m m e r s i o n p e r i o d of
a l u m i n u m s a m p l e s was 40 m i n and of m o l y b d e n u m s a m p l e s was up to 1000 hr. 11) RESULTS AND DISCUSSION P i n h o l e d e n s i t y in p y r o l y t i c oxide was i n v e s t i g a t e d a s a function of deposition t e m p e r a t u r e , deposition r a
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