The effect of copper additions on electromigration in aluminum thin films
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IN m e t a l l i c
c o n d u c t o r s , e l e c t r o m i g r a t i o n can be defined a s the t r a n s p o r t of m a t t e r by a n e l e c t r i c c u r r e n t . This p h e n o m e n o n has b e e n the object of m a n y s t u d i e s which w e r e e x t e n s i v e l y r e v i e w e d in 1963.1 G e n e r a l l y , it has b e e n found that a t o m s a r e pushed in the d i r e c t i o n of c a r r i e r motion by a p r o c e s s of m o m e n t u m exchange b e tween c h a r g e c a r r i e r s (usually e l e c t r o n s ) and a t o m s , which has b e e n a n a l y z e d t h e o r e t i c a l l y . 2'3 E l e c t r o m i g r a t i o n has b e e n o b s e r v e d in a l u m i n u m c o n d u c t o r s , in the c a s e of p u r e a l u m i n u m , 4'5 as w e l l a s in the c a s e of s o m e f o r e i g n e l e m e n t s , s i l v e r and zinc 6 i n a l u m i n u m . In the p a s t few y e a r s e l e c t r o m i g r a t i o n has b e e n i d e n tified a s a c a u s e of f a i l u r e , m o s t l y t h r o u g h the f o r m a tion of e l e c t r i c a l d i s c o n t i n u i t i e s in the thin f i l m a l u m i n u m c o n d u c t o r s which a r e u s e d for i n t e r c o r m e c t i o n p u r p o s e s in p l a n a r s i l i c o n d e v i c e s . B e c a u s e of this p r a c t i c a l i m p l i c a t i o n , e l e c t r o m i g r a t i o n in thin film a l u m i n u m c o n d u c t o r s has b e e n e x t e n s i v e l y s t u d i e d . 7-9 In e x p e r i m e n t s with buLk s a m p l e s , u s u a l l y conducted at t e m p e r a t u r e s close to the m e l t i n g point, it is u s u a l l y o b s e r v e d that t r a n s p o r t o c c u r s through a l a t t i c e diffusion m e c h a n i s m . At the m u c h l o w e r t e m p e r a t u r e s which a r e of c o n c e r n for thin f i l m s t u d i e s , t r a n s p o r t o c c u r s t h r o u g h g r a i n b o u n d a r y diffusion~ '1~ except (of c o u r s e ) in the c a s e of s i n g l e c r y s t a l f i l m s .12 The a d d i tion of copper to p o l y c r y s t a l l i n e a l u m i n u m f i l m s has b e e n found to i n c r e a s e c o n s i d e r a b l y the l i f e t i m e of c o n d u c t o r s s u b j e c t to high c u r r e n t d e n s i t y , t3 The a c t i v a t i o n e n e r g y for e l e c t r o m i g r a t i o n has b e e n studied by c o m p a r i s o n of the r a t e s of r e s i s t a n c e change at d i f f e r ent t e m p e r a t u r e s .14'ls Within e x p e r i m e n t a l e r r o r s , the a c t i v a t i o n e n e r g y is not modified by the a d d i t i o n of copp e r to a l u m i n u m . ~s E x p e r i m e n t a l r e s u l t s p r e s e n t l y at hand s h a l l be a n a l y z e d in the hope of a c h i e v i n g a p r e l i m i n a r y u n d e r s t a n d i n g of the r o l e of a l l o y a d d i t i o n s in electromigration.
F. M. d'HEURLE is Manager,Film Materials, IBM T. J. Watson Research Center,. Yorktown Heights, N. Y. 10598. This manuscript is based on an invited paper presented at the annual conference sponsored
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