Fig. 1. Schematic diagram of the optical system for large-area X-ray diffraction topography. The 300 mm- wide and monochromatic X-ray beam, obtained at the 200 m point apart from the bending- magnet source, was used to acquire topographs of a 300-mm-diameter silicon crystal sample. The manufacturing of 300-mm-diameter silicon w a f e r s , n o w u s e d a s s u b s t r a t e s f o r t h e U L S I fa b ri ca ti o n , re q u i re s d e ve l o p m e n t o f l a rg e -a re a X- ray diffraction topography with high strain-sensitivity to detect crystal imperfections. Such irregularities, e . g . g r o w t h s t r i a t i o n s , a n d s u r f a c e d a m a g e m a y a d v e r s e l y a f f e c t t h e e l e c t r i c a l c h a r a c t e r i s t i c s o f ULSI. Recently, we have created an experimental a p p a r a t u s d e s i g n e d t o a c q u i r e l a r g e - a r e a t o p o g r a p h s o f s i l i c o n c r y s t a l s a t t h e s e c o n d experimental hutch of beamline BL20B2 ; the set up i n c l u d e s t h e u s e o f a h o r i z o n t a l l y - w i d e a n d monochromatic X-ray beam made possible by 200 m d i s t a n c e b e t w e e n t h e h u t c h a n d t h e b e n d i n g - magnet source point [1] . U s i n g t h i s a p p a r a t u s , w e o b s e r v e d s u r f a c e d a m a g e r e s u l t i n g f r o m s l i c i n g a n d p o l i s h i n g , comparing the topographic images taken using low- ( 8 . 7 k e V ) , m e d i u m - ( 2 1 k e V ) a n d h i g h - ( 6 0 k e V ) LARGE-AREA X-RAY TOPOGRAPHY TO OBSERVE 300-MM-DIAMETER SILICON CRYSTALS Optics hutch Distance from the source point 0 m 42 m 200 m Imaging plate Detector Kapton window Long vacuum path Slit Be window Double-crystal monochromator X-ray source (Bending magnet) Sample Experimental hutch 2 e n e r g i e s X - r a y s [ 2 , 3 ] . T h e p - t y p e C Z s i l i c o n c r y s t a l s u s e d w e r e 3 0 0 - m m i n d i a m e t e r a n d 1 0 m m - t h i c k with a [100] surface orientation. After slicing with a wi re sa w, th e cr ys ta l su rf ac e wa s et ch ed sl ig ht ly , la pp ed , an d th en po li sh ed bo th me ch an ic al ly an d chemically. A s c h e m a t i c d i a g r a m o f t h e e x p e r i m e n t a l arrangement includes a 300-mm-wide X-ray beam, m o n o c h r o m a t i z e d b y t h e S i ( 3 1 1 ) d o u b l e - c r y s t a l mo no ch ro ma to r in th e op ti cs hu tc h ( Fi g. 1 ). Th is beam was incident on the sample crystal that was s e t o n t h e s a m p l e s t a g e o f t h e h o r i z o n t a l - a x i s precision goniometer of a tangential-bar type, at a glancing angle less than 1 degree. The energy of the X-ray beam was tuned to either 8.7, 21, 57 or 6 0 k e V b y o p e r a t i n g t h e d o u b l e - c r y s t a l m o n o c h r o m a t o r i n o r d e r t o a c q u i r e t o p o g r a p h s u s i n g a s y m m e t r i c r e f l e c t i o n s o f 3 1 1 , 5 1 1 , 1 2 2 2 and 911. Fig. 3. X-ray topographs of a 300-mm-diameter CZ silicon crystal after slicing, f o l l o w e d b y s l i g h t e t c h i n g . ( a ) a n d ( b ) w e r e t a k e n u s i n g t h e a s y m m e t r i c 5 1 1 reflection of 21 keV X-rays at the low-angle side and the high-angle side of the rocking curve, respectively. The arrow designates the diffraction vector g . Fig. 2. Calculated rocking curves from (100) silicon. Incident angle was fixed at 1 degree; the asymmetric 311, 511 and 911 reflections used 8.7, 21 and 60 keV X-rays, respectively. R o c k i n g c u r v e s w e r e c a l c u l a t e d f o r t h e as ym me tr ic 31 1, 51 1 an d 91 1 re fl ec ti on s at a fixed glancing angle of 1 degree on the basis of th e dy na mi ca l th eo ry of X- ra y di ff ra ct i on ( Fi g. 2 ). The maximum values of the gradient at the lo w- an gl e si de of th e cu rv es ar e 0. 14 8, 0. 76 1 a n d 4 . 5 5 2 a r c s e c - 1 f o r t h e 3 1 1 , 5 1 1 a n d 9 1 1 r e f l e c t i o n s , r e s p e c t i v e l y . T h e c u r v e f o r t h e asymmetric 12 2 2 reflection was similar to that f o r t h e a s y m m e t r i c 9 1 1 r e f l e c t i o n . T h e s e r e s u l t s i n d i c a t e t h a t u s e o f t h e h i g h e r - o r d e r as ym me tr i c re fl ec ti on of hi gh er -e ne rg y X- ra ys i m p r o v e s t h e s t r a i n s e n s i t i v i t y , w h e n t h e to po gr ap hs ar e ta ke n at th e an gl e po si ti on of half-peak intensity. Topographs, recorded on an imaging plate ( I P ) w i t h a p i x e l s i z e o f 1 0 0 μ m 2 , w e r e r e c o n s t r u c t e d 311 refl. 511 refl. 911 refl. Rotation Angle ( arcsec ) Normalized Intensity ( a.u. ) -10 0 10 20 -20 0.8 0 0.4 0.2 0.6 1 minute and wide strain-fields in the surface region of the sample. Using the asymmetric 12 2 2 reflection of 60 keV X- ra ys wi th hi gh er st ra in -s en si ti vi ty , we ex am in ed m i n u t e r e s i d u a l d a m a g e c a u s e d b y p o l i s h i n g . Ci rc ul ar de fe ct pa tt er ns an d mi cr os cr at ch im ag es ( F i g . 4 ) w e r e o b s e r v e d ; t h i s d e t e c t i o n m e t h o d a l l o w e d t h e i m p r o v e m e n t o f c u r r e n t p o l i s h i n g procedures. The use of extremely asymmetric reflections of a with an IP reader. The two topographs of a sliced a n d s l i g h t l y e t c h e d s a m p l e ( F i g . 3 a a n d b ) w e r e t a k e n u s i n g t h e a s y m m e t r i c 5 1 1 r e f l e c t i o n o f 2 1 k e V X - r a y s a t t h e l o w e r a n g l e s i d e a n d a t t h e higher angle side of the rocking curve; modification by image processing then created a circular sample shape. Long line images with equal intervals were i d e n t i f i e d a s s a w m a r k s c a u s e d b y s l i c i n g . T h e reversal of image contrast within the same areas of the two topographs demonstrates the presence of (a) (b) g 100 mm References [1] Y. Chikaura et al ., to be published in J. Phys. D: Appl. Phys. 34 (2001). [2] S. Kawado et al ., Progr. and Abstr. of 5 th Biennial C o n f . o n H i g h R e s o l u t i o n X - r a y D i f f r a c t i o n a n d Topography (X-TOP 2000), Sep. 2000, Poland, p.107. [3] S. Kawado et al ., submitted to Jpn J. Appl. Phys. 3 0 0 - m m - w i d e a n d m o n o c h r o m a t i c X - r a y b e a m e n a b l e s t h e a c q u i s i t i o n o f X - r a y t o p o g r a p h s a l l o v e r a 3 0 0 - m m - d i a m e t e r s i l i c o n c r y s t a l , u s i n g o n l y a s i n g l e X - r a y s e xp o su re . Th i s te ch n i q u e w i l l b e u se fu l i n c l a r i f y i n g i m p u r i t y i n h o m o g e n e i t y , d u b b e d g r o w t h s t r i a t i o n s , w i t h i n 3 0 0 - m m - d i a m e t e r CZ silicon crystals. Se ij i Ka wa do a , Sa to sh i Ii da b an d Yo sh in or i Chikaura c (a) Rigaku Corporation (b) Toyama University (c) Kyushu Institute of Technology E-mail: kawado @ rigaku.co.jp g 50 mm Fig. 4. X-ray topograph taken with the asymmetric 12 2 2 reflection of 60 keV X-rays after a polishing test. Circular patterns were identified as surface d a m a g e c a u s e d b y p o l i s h i n g . T h e a r r o w designates the diffraction vector g .
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