Infrared absorption characteristics of soluble and insoluble phosphorous-bearing oxide layers
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T H E r e l i a b i l i t y of a device i s a d v e r s e l y affected by the r e a c t i o n of the m e t a l l i z a t i o n with any f r e e phosphates available in the p h o s p h o r o u s - b e a r i n g oxide l a y e r , r e s u l t i n g in d e g r a d a t i o n of the m e t a l l i z a t i o n and loss of p a s s i v a t i o n quality. The technique p r o p o s e d is a n o n d e s t r u c t i v e test d e s i g n e d to d e t e r m i n e when the phosphorus is in a soluble (and p o s s i b l y r e a c t i v e ) or insoluble f o r m , via a shift in peak position of the i n f r a r e d c h a r a c t e r i s t i c of the P = O bond. A s i m p l e leach t e s t i s a l s o d e s c r i b e d to d e t e r m i n e the r e l a t i v e s o l u b i l i t y of the phosphorus in the p h o s p h o r u s - b e a r ing oxide o a y e r s . Use of the i n f r a r e d a b s o r p t i o n band technique to d e t e r m i n e the r e l a t i v e a m o u n t of phosphorus in a p h o s p h o s i l i c a t e - g l a s s l a y e r is r e p o r t e d by E. A. C o r l et al. 1 This technique was used in d e t e r m i n i n g extent of the r e a c t i o n of m e t a l l u r g y p a t t e r n s with the p h o s p h o s i l i c a t e - g l a s s l a y e r and p r e s e n t e d at the Fifth Annual Symposium on the P h y s i c s of F a i l u r e in E l e c t r o n i c s by M. M. Nanda et al.2 Fig. 1--Leach tester.
EXPERIMENTAL RESULTS Two pieces of a p p a r a t u s were u t i l i z e d to obtain the e x p e r i m e n t a l r e s u l t s r e p o r t e d . They were a P e r k i n E l m e r Model 521 Double G r a t i n g I n f r a r e d Spectrophot o m e t e r with s p e c u l a r r e f l e c t a n c e a t t a c h m e n t , and a s i m p l e vapor leach t e s t e r . The leach t e s t e r is shown in Fig. 1. The b e a k e r c o n t a i n i n g w a t e r is c o v e r e d by a q u a r t z plate with a hole(s) slightly l e s s than the dia m e t e r of a s i l i c o n wafer. The water is heated to 100~ and the wafer to be t e s t e d for s o l u b i l i t y is placed over the hole and exposed to the hot water vapor for v a r i o u s periods. Fig. 2 i s a d i a g r a m of the light path in the s a m p l i n g a r e a of the i n f r a r e d s p e c t r o p h o t o m e t e r . An oxidized wafer i s placed in the r e f e r e n c e b e a m in o r d e r that the i n f r a r e d a b s o r p t i o n exhibited (which is a m e a s u r e of the difference between the s a m p l e and r e f e r e n c e b e a m a b s o r p t i o n ) will be due only to the p r e s e n c e of the p h o s p h o r u s oxide l a y e r on the s a m p l e wafer. When a wafer with a p h o s p h o s i l i c a t e - b e a r i n g g l a s s l a y e r is studied, one o b s e r v e s an i n f r a r e d a b s o r p t i o n band in the r e g i o n of 1325 to 1275 cm -x. This is shown in Fig. 3, c u r v e b. The a b s o r p t i o n b a n d , due to p h o s p h o r u s , is at 1325 c m -1 and the a b s e n c e and p r e s e n c e of this b a n d in c u r v e s a and b is due to the a b
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