A B S T R A C T Czochralski silicon wafers with h i g h (34-40 p p m ) a n d low (22-28 p p m ) o x y g e n c o n t e n t were u s e d to c o m p a r e t h e precipitation characteristics of b o t h types of wafers s u b j e c t e d to a four-step getter a n n e a l procedure. T E M o b s e r v a t i o n s from t h e b u l k of t h e wafers t h a t received t h e full s i m u l a t e d t h e r m a l t r e a t m e n t revealed a precipitation r e g i m e t h a t b e g a n w i t h t h e n u c l e a t i o n of n e e d l e -s h a p e d f u n d a m e n t a l precipitates a n d evolved by c o a l e s c e n c e a n d defect colony g e n e r a t i o n into t h e f o r m a t i o n of o c t a h e d r a l precipitates. O x y g e n in CZ silicon wafers is i n c o r p o r a t e d from t h e silica crucible d u r i n g t h e g r o w t h of t h e crystal from the melt. This u n i n t e n d e d i m p u r i t y c a n be m a d e to h a v e a beneficial effect in device fabrication if t h e wafers are s u b j e c t e d to in situ gettering (1) or intrinsic gettering (2). A c c o r d i n g to t h e m e c h a n i s m outlined by T a n et al.(2), d u r i n g intrinsic g e t t e r i n g o x y g e n diffuses out of the surface of t h e wafer b u t precipitates in the bulk; o x y g e n precipitation in t h e b u l k generates defect centers t h a t act as low e n e r g y sites for h e a v y metallic i m p u r i t i e s such as Ni a n d Fe (3, 4). In addition, o x y g e n precipitates s o m e t i m e s p u n c h o u t dislocation loops (2) w h i c h p r o v i d e additional sites for m e t a l a t o m s (5). These i m p u r i t i e s are p r e v e n t e d from diffusing to t h e surface of t h e wafer a n d f o r m i n g electrically active c e n t e r s d e t r i m e n t a l to device p e r f o r m a n c e . O x y g e n precipitation, therefore, plays a direct role in t h e g e t t e r i n g of CZ silicon. T h u s it is i m p o r t a n t to u n d e r s t a n d its d y n a m i c s to optimize t h e intrinsic gettering effect. One t e c h n i q u e particularly suited to s t u d y p r e c i p i t a t i o n is t r a n s m i s s i o n electron m i c r o s c o p y (TEM), owing to its h i g h r e s o l u t i o n in i m a g i n g precipitates a n d t h e i n f o r m a t i o n it gives on t h e crystallographic n a t u r e of associated defects.We u s e d wafers with two different o x y g e n contents. One set of wafers h a d h i g h (34-40 p p m ) a n d a n o t h e r set low (22-28 ppm) o x y g e n content. High o x y g e n wafers are exp e c t e d to s h o w a larger v o l u m e of o x y g e n precipitation. L o w o x y g e n wafers, on t h e other hand, are preferred for s o m e device fabrication because, as we h a v e r e p o r t e d previously (6), t h e surface defect density of finished devices u s i n g low o x y g e n wafers is lower t h a n in h i g h o x y g e n wafers.A gettering p r o c e d u r e we h a v e d e s c r i b e d previously (6) ( s h o w n in Fig. 1) was used in this study. T h e evolution of t h e precipitates with thi...