Aluminum metallization and contacts for integrated circuits
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contained contact openings of v a r i o u s g e o m e t r i e s and s i z e s . The p a t t e r n i s shown in Fig. 2. Our p r o c e d u r e was to grow about 8000~ of SiO2 in s t e a m at 1000~ onto 0.45 to 0.55 o h m - c m , n - t y p e s i l i c o n wafers. The contact p a t t e r n was etched with b u f f e r e d HF. Then 8000/k of 99.99 pct A1 was e v a p o r a t e d from three t u n g s t e n b o a t s , f i r e d in s e q u e n c e at about 1 • 10 -s t o r r . The r e s u l t i n g a l u m i n u m has a bulk r e s i s t i v i t y of 2.75 • 10 -6 o h m - c m . A s e c o n d p a t t e r n c o n s i s t i n g of two d i f f e r e n t size s q u a r e s , having a r e a s of 625 and 2500 p sq, was used in c o n j u n c t i o n with other wafers of v a r i o u s r e s i s t i v i t i e s and oxidation conditions. These wafers were designed to r e v e a l the effects of i n t e r f a c e s t r e s s , i m p u r i t y type, and s t e a m or d r y oxygen oxidation on t r i angle density and l a t e r a l a l u m i n u m p e n e t r a t i o n b e neath the SiO~. Alloying was conducted at a p p r o x i m a t e l y 480~ for all these wafers. F o r a l l o y i n g , two t e c h n i q u e s were used. In the t e m p e r a t u r e r a n g e above 470~ a M a r s h a l l f u r n a c e was used with a quartz wafer holder. The q u a r t z holder was pulled from the f u r n a c e , the wafer chip quickly placed (aluminum m e t a l l i z a t i o n up) on the holder which was i m m e d i a t e l y r e t u r n e d to the s a m e location in the f u r n a c e from which it had been withdrawn. F o r t e m p e r a t u r e s below 470~ a flat r e s i s t a n c e h e a t e r coy-
EXPERIMENTAL In our f i r s t a t t e m p t to use the single m e t a l l i z a t i o n p r o c e s s , we e n c o u n t e r e d a p e c u l i a r effect n e v e r seen in the t w o - s t e p p r o c e s s - - t r i a n g u l a r a l u m i n u m growths b e n e a t h the SiO2 at the contact step a s s e e n in Fig. 1. A s h o r t has o c c u r r e d in this case. M a x i m u m t r i a n g l e size s e e m s to be defined by the contact g e o m e t r y . To study this p r o b l e m , a s p e c i a l m a s k set was made which CLYDE H. LANE is Physicist, Rome Air Development Center, Griffiss Air Force Base, N. Y. This manuscript is based on a paper presented at the IMD Electronic Materials Conference, August 24-27, 1969, in Boston, Mass. METALLURGICALTRANSACTIONS
Fig. 1--Electrical short and missing aluminum resulting from high temperature alloying. VOLUME 1,MARCH 1970-713
e r e d with a thin sheet of q u a r t z was used. A folded sheet of copper was placed on the q u a r t z . The chip and t h e r m o c o u p l e was i n s e r t e d into the space b e t w e e n the folded copper sheet. Helium gas was p a s s e d over the whole a s s e m b l y d u r i n g a l l o y i n g and cooling. High p u r i t y n i t r o g e n was used in the tube f u r n a c e . F o r lapping p u r p o s e s , the chips were e n c a p s u l a t e d in polyvinyl chloride. The f i r s
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