electron-beam doping-electron radiation effects in impurity overlayers and semiconductor substrates

Journal of Elec tronic Materials, Vol. 1 4 , N o . 2 , 1985

E L E C T R O N - B E A M D O P I N G - E L E C T R O N R A D I A T I O N E F F E C T SIN I M P U R I T Y O V E R L A Y E R S A N D

S E M I C O N D U C T O R S U B S T R A T E S - -

T a k a o W a d a , M i c h i h i k o T a k e d a and K y o i c h i r o Y a s u d a *

D e p a r t m e n t of E l e c t r o n i c s , N a g o y a I n s t i t u t e ofT e c h n o l o g y , G o k i s o , S h o w a , N a g o y a 466 J a p a n

G o v e r n m e n t I n d u s t r i a l R e s e a r c h I n s t i t u t e ,N a g o y a , H i r a t e , K i t a , N a g o y a 462 J a p a n

(Received June 20, 1984)

3-9 M e V e l e c t r o n s w e r e used to i n t r o d u c e i m p u r i t yGe a t o m s into Si w a f e r s from Ge s h e e t s , w h i c h arein c o n t a c t w i t h a Si s u r f a c e at 2 0 - 6 0 ° C in w a t e rb a t h . C o n c e n t r a t i o n - d e p e n d e n t d i f f u s i v i t i e s of~ i 0 - 1 8 - i 0 -14 c m 2 s e c - i for Ge in Si w e r e m e a s u r e d .A c t i v a t i o n e n e r g i e s of s p u t t e r i n g y i e l d for Geand of the d i f f u s i v i t y of Ge in Si are e s t i m a t e dto be ~ 0 . 3 eV and N 0 . 5 8 eV, r e s p e c t i v e l y . In acase of h o t ( ~ 2 5 0 ° C ) i r r a d i a t i o n in ~ i x l 0 -3 T o r rv a c u u m , also the s i m i l a r c o n c e n t r a t i o n p r o f i l e sof i m p u r i t y a t o m s in the s u b s t r a t e s w e r e o b s e r v e d .

Key w o r d s : e l e c t r o n - b e a m d o p i n g , h i g h - e n e r g ye l e c t r o n b o m b a r d m e n t , i m p u r i t y d o p i n g , d i f f u s i o n ,s i l i c o n and g e r m a n i u m .

I n t r o d u c t i o n

The p h y s i c a l p r o p e r t i e s of s e m i c o n d u c t o r si r r a d i a t e d by h i g h e n e r g ~ e l e c t r o n s h a v e b e e ns t u d i e d b y m a n y w o r k e r s . -4) Ion i m p l a n t a t i o n hasb e e n d e v e l o p e d into a s u c c e s s f u l t e c h n i q u e ford o p i n g s e m i c o n d u c t o r m a t e r i a l s . It is w e l l k n o w n

171

0361-5235/85/1401-017153.00 © 1985 AIME

172 Wada , Takeda and Yasuda

that ion i m p l a n t a t i o n in s e m i c o n d u c t o r s isa c c o m p a n i e d by s e v e r e r a d i a t i o n d a m a g e i n t r o d u c e dw i t h the i m p l a n t a t i o n p r o c e s s . 5) In s i l i c o n , w i t hl o w ion d o s e s , the d a m a g e t a k e s the from ofa m o r p h o u s z o n e s , 6) and w h e n i r r a d i a t i o n isc o n t i n u e d , the z o n e s o v e r l a p to from a c o n t i n u o u sa m o r p h o u s l a y e r .

The i m p o r t a n t b a s i s for the use of e l e c t r o n slies in the fact that as long as the e n e r g y ofthe e l e c t r o n s is c l o s e to the d i s p l a c e m e n tt h r e s h o l d , it is p r e s u m e d that o n l y s i n g l eF r e n k e l p a i r s are f o r m e d . E l e c t r o n i r r a d i a t i o na v o i d s the c o m p l i c a t i o n a t t e n d a n t upon theg e n e r a t i o n of c o m p l e x d a m a g e r e g i o n s p r e s u m e d too c c u r in n e u t r o n and h e a v y - c h a r g e d p a r t i c l ei r r a d i a t i o n .

A n e w m e t h o d of e l e c t r o n b e a m d o p i n g wasr e p o r t e d by one of the a u t h o r s W a d a . 7 , 8) Thet e c h n i q u e e m p l o y s an i m p u r i t y s h e e t in c o n t a c tw i t h the s e m i c o n d u c t o r s u r f a c e w h i c h is b o m b a r d e dw i t h h i g h e n e r g y e l e c t r o n s . 7 - 1 4 )

In the p r e s e n t p a p e r the i n t r o d u c t i o n s of Gei m p u r i t i e s into Si at 2 0 - 6 0 ° C in w a t e r b a t h , andat ~ 2 5 0 ° C in v a c u u m are i n v e s t i g a t e d . Thed i f f u s i v i t y of Ge i m p u r i t y in Si, an a c t i v a t i o ne n e r g y of s p u t t e r i n g y i e l d for Ge and an a c t i v a -tion e n e r g y of the d i f f u s i v i t y of Ge are e s t i m a -ted. D e p e n d e n c e s of i m p u r i t y c o n c e n t r a t i o n s on Ges h e e t t h i c k n e s s and on e l e c t r o n e n e r g y areo b s e r v e d .

E x p e r i m e n t a l p r o c e d u r e s

The s a m p l e s u s e d in the e x p e r i m e n t s were P-Si ( B - d o p e d ( i i i ) , ~ 2 5 - 5 0 ~ . c m ) w i t h an a r e a of5x5 m m 2 ( t = 0 . 3 5 mm). t r e p r e s e n t s the t h i c k n e s sof s u b s t r a t e s or i m p u r i t y s h e e t s . The Ge c r y s t a l swere S b - d o p e d ( i i i ) w a f e r s w i t h d i m e n s i o n s of5 x 5 x t ( ~ O . l - l ) m m 3. The s u r f a c e of the Ge s h e e t inc o n t a c t w i t h the Si w a f e r w a s i r r a d i a t e d w i t h af l u e n c e of ( l - l O ) x l 0 1 7 e l e c t r o n s cm -2 at 3-9 M e Vf r o m a 2-10 M e V e l e c t r o n l i n e a r a c c e l e r a t o r w i t ha p u l s e w i d t h of 3.5 ~s h a v i n g a 200 Hz dutyc y c l e and an a v e r a g e e l e c t r o n b e a m c u r r e n t of 40-

Electron-Beam Doping-Electron Effects 173

I Is,

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(a) S c h e m a t i c d i a g r a m of e l e c t r o n b e a md o p i n g . (b) S c h e m a t i c d i a g r a m ofe l e c t r o n b o m b a r d m e n t at 2 0 - 6 0 ° C and (c)at 2 5 0 ° C in v a c u u m .

f f " l ~ l : :'~/////H///~'t'- r--l]

50 ~ A - c m -2 ( F i g . l . ( a ) ) .In the case of 2 0 - 6 0 ° C i r r a d i a t i o n , the

s a m p l e s w e r e put in a c i r c u l a t i n g w a t e r b a t h ,w h i c h w a s k e p t at a c o n s t a n t t e m p e r a t u r e by u s i n ga t h e r m o r e g u l a t o r , as s h o w n in F i g . l . ( b ) . Thed e t a i l of the s a m p l e m o u n t at ~ 2 5 0 ° C i r r a d i a t i o nin v a c u u m is s c h e m a t i c a l l y i l l u s t r a t e d in F i g . l(c). The i n t r o d u c t i o n of i m p u r i t y a t o m s in Si w a sm e a s u r e d u s i n g b o t h R u t h e r f o r d b a c k s c a t t e r i n gs p e c t r o s c o p y ( R B S ) and s e c o n d a r y ion m a s ss p e c t r o s c o p y ( S I M S ) .

P r e c e d i n $ d i s c u s s i o n

T h e r a n g e of e l e c t r o n s at 7 M e V (3 MeV) inSi and Ge are ~ b o u t 1 5 ( 6 . 4 ) and 5 . 6 ( 2 . 4 ) mm,r e s p e c t i v e l y . I ) So, the i m p u r i t y s h e e t l a y e r iss u f f i c i e n t l y thin to a l l o w the i r r a d i a t i n ge l e c t r o n s to p e n e t r a t e into the s u b s t r a t e w i t h o u ta s i g n i f i c a n t loss in k i n e t i c e n e r g y . T h ep r o d u c t i o n r a t e s of d e f e c t s in Si and Ge for 7M e V e l e c t r o n i r r a d i a t i o n a r e a b o u t 8 and 9 cm -I,1 6 , 1 7 ) r e s p e c t i v e l y .

W h e n the f l u x and e n e r g y s p e c t r u m of r e c o i la t o m s c r o s s i n g the i n t e r f a c e b e t w e e n the Ge l a y e rand the s u b s t r a t e are c a l c u l a t e d , the d e p t h

174 W a d a , Takeda and Yasuda

d i s t r i b u t i o n of the r e c o i l i m p u r i t y a t o m s w i t h i nthe s u b s t r a t e can be e s t i m a t e d . The e n e r g ys p e c t r u m of r e c o i l a t o m s d u r i n g e l e c t r o n b o m b a r d -m e n t can be o b t a i n e d from an e q u a t i o n g i v e n byM c k i n l e y and F e s h b a c h I)

= ~ / Z e 2 ~ 2 (B-~y2) Tmd ~ M c F ~ m c 2 /

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F i g . 2 . T h e o r e t i c a l n u m b e rof r e c o i l s c r o s s i n g ani n t e r f a c e as a f u n c t i o nof r e c o i l e n e r g y .


T m is the m a x i m u m r e c o i l e n e r g y

m ( E + 2 m c 2 ) ETm= 2 M mc 2 '

E is the e l e c t r o n e n e r g y , T the r e c o i l k i n e t i ce n e r g y and M the m a s s of a t o m .

F i g . 2 s h o w s the c a l c u l a t e d t y p i c a l r e c o i ls p e c t r u m , i.e. the n u m b e r of r e c o i l s c r o s s i n g ani n t e r f a c e as a f u n c t i o n of the r e c o i l e n e r g y . Them a x i m u m r e c o i l e n e r g y is a b o u t 3.4 K e V for i0 M e Ve l e c t r o n s . The r a n g e of i m p l a n t e d ion in Si hasb e e n c a l c u l a t e d as a f u n c t i o n of ion e n e r g y 18)By u s i n g the b o t h r e s u l t s , the p e n e t r a t i o nd i s t r i b u t i o n d u r i n g the r e c o i l i m p l a n t a t i o n of Geinto Si by i0 M e V e l e c t r o n b o m b a r d m e n t is t h e o r e -t i c a l l y o b t a i n e d as a f u n c t i o n of d e p t h , as s h o w nin F i g . 3 . The i m p l a n t e d i m p u r i t y a t o m s ared i s t r i b u t e d w i t h i n the Si c r y s t a l up to a d e p t h

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F i g , 3 . T h e o r e t i c a l c o n c e n t r a -t i o n p r o f i l e s of r e c o i l a t o m sinto Si as a f u n c t i o n of d e p t h .


of a b o u t 30 A b e l o w the s u r f a c e .H o w e v e r , in the p r e s e n t e x p e r i m e n t s the

c o n c e n t r a t i o n p r o f i l e s of Ge a t o m s into Si areo b t a i n e d up to a d e p t h of a b o u t 0.6 ~ m b e l o w thes u r f a c e ( ( s e e F i g . 9 . ( a ) ) ) . As the i n c i d e n te l e c t r o n s p a s s t h r o u g h the s h e e t into s i l i c o n ,d e f e c t s in Si are i n t r o d u c e d from the s u r f a c e upto thd r a n g e of e l e c t r o n s . T h e n , m e c h a n i s m s forsuch p r o f i l e s of Ge a t o m s are not o n l y the r e c o i lp r o c e s s of Ge a t o m s , but a l s o e n h a n c e d d i f f u s i o nof i m p u r i t y a t o m s in Si.

F i g . 4 s h o w s the t h e o r e t i c a l e n e r g y s p e c t r aof e l e c t r o n s at d i f f e r e n t d e p t h in Si fori n c i d e n t e l e c t r o n e n e r g y E o of 6 MeV. Thec a l c u l a t e d r e s u l t s are o b t a i n e d by u s i n g aS u g i y a m a , s p r o g r a m 19) of a M o n t e C a r l o s i m u l a t i o nfor the t h e o r y of fast e l e c t r o n p e n e t r a t i o n inm a t t e r . The c a l c u l a t i o n s are done for i000h i s t o r i e s and A E = 0 . 0 2 M e V , w h e r e AE m e a n s the

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F i g . 4 . T h e o r e t i c a l e n e r g ys p e c t r a of e l e c t r o n s at 6 M e Vin Si w i t h d i f f e r e n t d e p t h s .


a v e r a g e e n e r g y lost in p a s s i n g t h r o u g h them a t e r i a l . In a case of E o = 4 0 0 KeV, the t h e o r e t i -cal r e s u l t s are in good a g r e e m e n t w i t h thee x p e r i m e n t a l r e s u l t s . 20) W i t h i n c r e a s i n g d e p t h ,a p e a k v a l u e of the s p e c t r a d e c r e a s e s and itsw i d t h i n c r e a s e s . M o n t e C a r l o s i m u l a t i o n tooka c c o u n t of m u l t i p l e s c a t t e r i n g of e l e c t r o n ,s t r a g g l i n g of e l e c t r o n e n e r g y loss by i o n i z a t i o nand e x c i t a t i o n , p r o d u c t i o n of k n o c k on e l e c t r o n sand p r o d u c t i o n of b r e m s t r a h l u n g p h o t o n s . Forp h o t o n p e n e t r a t i o n , p h o t o e l e c t r i c e f f e c t s ,c o m p t o n e f f e c t , p a i r p r o d u c t i o n and a n n i h i l a t i o nr a d i a t i o n f r o m p o s i t r o n in rest or in f l i g h t w e r ealso c o n s i d e r e d .

W h e n e v e r a c h a r g e d p a r t i c l e l o s e s e n e r g y ina s o l i d , e l e c t r o n - h o l e p a i r s ( e h p ) are p r o d u c e d .The r a t e of g e n e r a t i o n , g, of e h p ' s p e r u n i t timeby an i n c i d e n t e l e c t r o n b e a m can be e s t i m a t e df r o m the r e l a t i o n

i dE d_~ (2)g E dx dt

w h e r e E is the e n e r g y for f o r m a t i o n of ehp (E inGe and Si are 2.84 and 3.23 eV, r e s p e c t i v e l y ) , 21)d E / d x ~ l . 7 and 1.6 M e V cm 2 g-l. e l e c t r o n - i 22) arethe e n e r g y loss per cm of p a t h by a fast e l e c t r o nin Ge and Si, and d ~ / d t is the i r r a d i a t i o n r a t e .I r r a d i a t i o n at a r a t e of 2 . 5 x i 0 1 4 e l e c t r o n s cm -2sec -I (an a v e r a g e b e a m c u r r e n t of 40 ~ A - c m -2)w o u l d r e s u l t in g ~ 3 x l O20 e h p ' s c m - 3 . s e c -I forSi The ehp g e n e r a t i o n p r o d u c e s an ehp c o n c e n t -r a t i o n of c = g T , w h e r e T is the e x c e s s c a r r i e rl i f e t i m e . C = 8 x l 0 1 7 c m -3 for Ge ( 3 x I 0 1 7 9 ~ 3 forSi), s i n c e T is on the o r d e r of 1 m s l 4 J - ( A c t u a l l yT is d i f f i c u l t to e v a l u a t e , s i n c e it is v e r ys e n s i t i v e to the a m o u n t of d e f e c t s and t h e r e f o r eit w i l l v a r y d u r i n g the i r r a d i a t i o n ) .

W h e n such a n u m b e r of c o n d u c t i o n e l e c t r o n sa n d / o r h o l e s in Ge (Si) r e c o m b i n e at d e f e c t s v i an o n - r a d i a t i v e t r a n s i t i o n s , m o b i l i t y e n h a n c e m e n tof i m p u r i t y a t o m s m a y be c a u s e d by the e n e r g yr e l e a s e d in t h e s e p r o c e s s e s .

On the o t h e r h a n d , the B o u r g o i n m e c h a n i s m 23)o c c u r s w h e n d i f f e r e n t c h a r g e - s t a t e s r e v e r s e the

178 W a d a , T a k e d a and Yasuda

p o s i t i o n s of t h e i r r e s p e c t i v e m i n i m u m of p o t e n t i a le n e r g y and d i f f u s i o n s a d d l e p o i n t s . A c h a n g e inthe c h a r g e s t a t e of a m i g r a t i n g d e f e c t u s u a l l yg i v e s rise to a c h a n g e in the m i g r a t i o n e n e r g yEm.

B o t h the e n e r g y r e l e a s e and the B o u r g o i nm e c h a n i s m s may a p p l y for two d i f f e r e n t c h a r g es t a t e s (0, +I) or (0, -i) of the i n t e r s t i t i a lw h e r e O, +i and -i m e a n the c h a r g e s t a t e . 23) '

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F i g . 5 . (a) B a c k s c a t t e r -ing s p e c t r a for thei r r a d i a t e d Si in ther a n d o m c o n d i t i o n s atd i f f e r e n t i r r a d i a t i o nt e m p e r a t u r e s .(b) C o n c e n t r a t i o n of Gei m p u r i t y as a f u n c t i o nof r e c i p r o c a l i r r a d i a -tion t e m p e r a t u r e .

36

Electron-Beam Doping-Elec tronEffects 179

E x p e r i m e n t a l r e s u l t s and d i s c u s s i o n

In the case of Ge o v e r l a y e r s ( t ~ 0 . 5 mm) andSi s u b s t r a t e , the b a c k s c a t t e r i n g s p e c t r a in ther a n d o m c o n d i t i o n s by 1.4 M e V He + ions are s h o w nin F i g . 5 . (a) for the s p e c i m e n s i r r a d i a t e d at 2 0 ° C ,40 ° and 60°C w i t h a t o t a l f l u e n c e of ~ 5 . 1 x l O 17e l e c t r o n s cm -2 at 7 MeV. The n u m b e r of c o u n t s ofGe p e a k s in Si i n c r e a s e s w i t h i n c r e a s i n gi r r a d i a t i o n t e m p e r a t u r e . The e x p r e s s i o n of the Gec o n c e n t r a t i o n r a t i o is g i v e n by

C G [S] Pe NGe Ge Si

CSi NSi [ S ] s i PGe(3)

w h e r e C m e a n a c o n c e n t r a t i o n , N the n u m b e r ofc o u n t s , [S] the b a c k s c a t t e r i n g e n e r g y lossp a r a m e t e r and P the d i f f e r e n t i a l s c a t t e r i n g c r o s ss e c t i o n s . The m a x i m u m Ge c o n c e n t r a t i o n s CGee s t i m a t e d f r o m the b a c k s c a t t e r i n g s p e c t r a in thef i g u r e are s h o w n in F i g . 5 . ( b ) as a f u n c t i o n ofr e c i p r o c a l i r r a d i a t i o n t e m p e r a t u r e . An a c t i v a t i o ne n e r g y of s p u t t e r i n g y i e l d for Ge a t o m s into Siis e s t i m a t e d to be a b o u t 0.3 eV f r o m this f i g u r e .

The i n t e n s i t y r a t i o s of 74Ge + ions to 2 8 S i +ions in the case of Ge ( t ~ 0 . 5 m m ) / S i i r r a d i a t e dby the same c o n d i t i o n s as d e s c r i b e d a b o v e a r es h o w n in F i g . 6 " ( a ) as a f u n c t i o n of d e p t h m e a s u r -ed f r o m the Si f r o n t s u r f a c e , w h i c h is in c o n t a c tw i t h the o v e r l a y e r . The SIMS m e a s u r e m e n t s w e r ep e r f o r m e d b y u s i n g the p r i m a r y i o n (02 + ) b e a m( d i a m e t e r 1 mm~) w i t h an ion e n e r g y of 7 K e V ina 1 . 5 x 1 0 -7 T o r r v a c u u m . For Si w a f e r s i r r a d i a t e dw i t h o u t i m p u r i t y s h e e t s , the Ge + p e a k s d i s a p p e a r -ed. T h e d i f f u s i o n p r o f i l e is not a c o m p l e m e n t a r ye r r o r f u n c t i o n . T h i s s u g g e s t s t h a t thed i f f u s i v i t y is c o n c e n t r a t i o n d e p e n d e n t Thea n a l y s i s of B o l t z m a n n 24) and M a t a n o 25) is u s e d too b t a i n the c o n c e n t r a t i o n C d e p e n d e n c e of thed i f f u s i v i t y D (c). A s s u m i n g a c o n s t a n t s u r f a c ec o n c e n t r a t i o n C o d u r i n g the e n t i r e d i f f u s i o n ,the e q u a t i o n of D(c) in the case of the S I M S


w=~ lo . 2

q

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E = 7 M e VO = 5 x i 0 e l c m 2

I , I , I a0.01 0 . 0 2 0.03

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(a)

0.04

F i g . 6 (a) I n t e n s i t yr a t i o s of 7 4 G e + to 2 8 S i2 8 S i + in Si s u b s t r a t eas a f u n c t i o n of d e p t hf r o m the f r o n t s u r f a c eof Si. (b) D i f f u s i v i t yD as a f u n c t i o n ofd e p t h from the Sis u r f a c e , and (c) Gei m p u r i t y c o n c e n t r a t i o nat 4 0 ° C . (d) D i f f u s i -v i t y of Ge i m p u r i t y inSi as a f u n c t i o n ofr e c i p r o c a l i r r a d i a t i o nt e m p e r a t u r e

i 0-I~

t(~ I s

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o , D , ex~- 0k - - ~ Tv )

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(d)

m e a s u r e m e n t s is g i v e n by


I Ir x

1 I r o ( K s I r + K i ) 2 d I rD(c) = 2t ( 1 dI r (4)

2 dx ) Ir(K I +K.)

s r m

w h e r e I i and I s are the SIMS s i g n a l i n t e n s i t i e sof i m p u r i t y ions a n d s u b s t r a t e i o n s , r e s p e c t i v e -ly, w h i c h are c o r r e c t e d for the n a t u r a la b u n d a n c e of the i s o t o p e , K i and K s are thes p u t t e r e d ion y i e l d of i m p u r i t y ions and

s u b s t r a t e i o n s , r e s p e c t i v e l y , and I r is ther a t i o of I i to I s . The c a l c u l a t e d v a l u e s of D(c)at the i r r a d i a t i o n t e m p e r a t u r e of 40°C are s h o w nin Fig.6"(b) and (c) as a f u n c t i o n of d e p t h f r o m theSi s u r f a c e and i m p u r i t y c o n c e n t r a t i o n r e s p e c t i v e -ly. The v a l u e of D(c) d e c r e a s e s w i t h i n c r e a s i n gi m p u r i t y c o n c e n t r a t i o n and i n c r e a s e s w i t h thed e p t h f r o m the Si s u r f a c e . The v a l u e s of D(c) atx < O . 0 1 um and x > O . O l ~m for Ge are o b s e r v e d tobe 1 0 - 1 8 - 1 0 -16 c m 2 s e c -I and ~ I 0 - 1 6 - i 0 -14 c m 2 s e c - ~r e s p e c t i v e l y . The v a l u e of C o is e s t i m a t e d to b e~ l . 4 x l 0 2 O c m -3. The r e s u l t a n t p l o t is m a i n l yc o m p o s e d of t h r e e c u r v e s . It is s u g g e s t e d thatt h r e e k i n d s of s p e c i e s d i f f u s e into thes u b s t r a t e . The d i f f u s i v i t i e s of D(c) at c = i x l 0 2 0c m -3 for 20 ° , 40 ° and 6 0 ° C , w h i c h are e s t i m a t e dby the a n a l y s i s of B o l t z m a n n and M a t a n o from thec u r v e s of F i g . 6 . ( a ) , are s h o w n in F l a . ( d ) as af u n c t i o n of r e c i p r o c a l i r r a d i a t i o n t e m p e r a t u r e .F r o m this c u r v e , an a c t i v a t i o n e n e r g y for thed i f f u s i v i t y in Si is o b t a i n e d to be a b o u t 0.58eV. F i g . 6 " ( d ) s u g g e s t s that t o t a l Ge a t o m sd i f f u s e d into the Si s u b s t r a t e m i g h t h a v e theform

N G e / c m 2 = N o . ( D T ) I/2 (5)

and t h e r e f o r e s h o w an a c t i v a t i o n e n e r g y ofa p p r o x i m a t e l y 0 . 5 8 / 2 eV (see F i g . 5 " ( b ) ) .

F i g . 7 s h o w s the i n t e n s i t y r a t i o of 7 4 G e +


lrradlali~n In v a c u u m

E = 7 M e V

~b= 5 x I01"/e I c rn2¢ •

I0 -3

10"~

1if:

10"

I0-2t

Oepth (~m)

F i g . 7 . I n t e n s i t y r a t i o s of7 4 G e + to 2 8 S i + in Si i r r a d i a t e din v a c u u m as a f u n c t i o n ofd e p t h f r o m the f r o n t s u r f a c eof Si.

ions to 2 S S i + ions in the case of the i r r a d i a t i o nin ~i0 -3 Tort v a c u u m for Ge ( t ~ 0 . 5 m m ) / S i . Thes a m p l e w a s i r r a d i a t e d w i t h a f l u e n c e of N 4 . 7 x 1 0 1 7e l e c t r o n s cm -2 at ~ 2 5 0 ° C . The v a l u e s of D(c)r a n g e from 10 -18 to 4x10 -15 c m 2 s e c - l . The v a l u eof C o is e s t i m a t e d to be ~ 5 x i 0 2 0 c m - 3 . Thec o n c e n t r a t i o n p r o f i l e of i m p u r i t y a t o m s in Sii r r a d i a t e d in v a c u u m is s i m i l a r to thati r r a d i a t e d in w a t e r b a t h . It s u g g e s t s thati n t e r f a c i a l o x i d e s and c a p i l l a r y w a t e r l a y e r s inthe c o n t a c t of the o v e r l a y e r and the s u b s t r a t em i g h t not be s e r i o u s l y a f f e c t e d for e l e c t r o n -b e a m d o p i n g .

The r e l a t i v e i n t e n s i t i e s of Ge i m p u r i t ya t o m s are i n d i c a t e d in F i g . 8 as a f u n c t i o n ofi r r a d i a t i o n e l e c t r o n e n e r g y at d i f f e r e n t d e p t h sf r o m the Si s u r f a c e . The s a m p l e s w e r e i r r a d i a t e d


02j

-- lo-S

E l e c t r o n energy (MeV)

F i g . 8 . I n t e n s i t y r a t i o s of7 4 G e + to 2 8 S i + in Si as af u n c t i o n of i r r a d i a t i o ne l e c t r o n e n e r g y at d i f f e r e n td e p t h s f r o m the Si s u r f a c e .

w i t h a f l u e n c e of ~ 5 x 1 0 1 7 e l e c t r o n s cm -2 at 3,5,7 and 9 M e V at 6 0 ° C , and the t h i c k n e s s of GeS h e e t s is ~0.5 mm. T h e 5-7 M e V e l e c t r o ni r r a d i a t i o n b e c o m e s to o b t a i n a m a x i m u m s p u t t e r -ing y i e l d .

F i g . 9 . ( a ) s h o w s the r e l a t i v e i m p u r i t yi n t e n s i t i e s of Ge a t o m s in Si as a f u n c t i o n ofd e p t h from the Si s u r f a c e at d i f f e r e n t Ge w a f e rt h i c k n e s s e s . T h e s e s a m p l e s w e r e i r r a d i a t e d w i t ha t o t a l f l u e n c e of ~ 5 x i 0 1 7 e l e c t r o n s cm -2 at 7MeV. The r e l a t i v e i m p u r i t y i n t e n s i t i e s of Gea t o m s at a d e p t h of 0.i ~m in Si are i n d i c a t e d inF i g . 9 " ~ ) a s a f u n c t i o n of Ge o v e r l a y e r t h i c k n e s s .At the t h i c k n e s s of ~ 0 . 2 mm, the i n t e n s i t y r a t i oof 7 4 G e + ions to 2 8 S i + ions b e c o m e s a m a x i m u mv a l u e .

184 Wada , Takeda and Yasuda

LO

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10-3~ • t=013 mm

h. :t \ o °5I" ~ . , 0.6L \ , o 08

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0 0.2 0.4 0.6 0.8 1.0THICKNESS (ram)

(b)

(a),~w~ , I ,v 0 0.1 0.2

D E P T H ( ~ m )

F i g . 9 . (a) I n t e n s i t y r a t i o s of 7 4 G e + to 2 8 S i +in Si as a f u n c t i o n of d e p t h , f r o m the Sis u r f a c e at d i f f e r e n t Ge s h e e t t h i c k n e s s e s . (b)I n t e n s i t y r a t i o s of 74Ge + to 2 8 S i + in Si as af u n c t i o n of Ge s h e e t t h i c k n e s s .

1.2

S u m m a r y

A n e w e l e c t r o n - b e a m d o p i n g into Si b y u s i n gh i g h e n e r g y e l e c t r o n b o m b a r d m e n t is i n v e s t i g a t e d .An i m p u r i t y s h e e t of Ge is in c o n t a c t w i t h Sis u r f a c e a n d the s u r f a c e of the i m p u r i t y s h e e t isb o m b a r d e d w i t h 3-9 M e V e l e c t r o n s . C o n c e n t r a t i o n -d e p e n d e n t d i f f u s i v i t i e s for Ge in Si areo b t a i n e d . A c t i v a t i o n e n e r g i e s of s p u t t e r i n g y i e l dfor Ge and of the d i f f u s i v i t y of Ge in Si arem e a s u r e d .

A c k n o w l e d g e m e n t s

The a u t h o r s w o u l d like to e x p r e s s t h e i r


t h a n k s to M e s s r s K . Y a s u d a and H . M a s u d a of theG o v e r n m e n t I n d u s t r i a l R e s e a r c h I n s t i t u t e ofN a g o y a , for t h e i r h e l p in c o n n e c t i o n w i t hi r r a d i a t i o n of the s a m p l e , and V a n de G r a a f fg r o u p of the G o v e r n m e n t I n d u s t r i a l R e s e a r c hI n s t i t u t e of N a g o y a , for t h e i r h e l p in RBSm e a s u r e m e n t s .

1)

2)

3)

4)

5)

6)

7)

8)

9)

i0)

11)

12)

R e f e r e n c e

J . W . C o r b e t t , E l e c t r o n R a d i a t i o n D a m a g e inS e m i c o n d u c t o r s a n d M e t a l s ( A c a d e m i c P r e s s ,N e w Y o r k and L o n d o n , 1 9 6 6 ) .H . Y . F a n and K . L a r k - H o r o v i t z , E f f e c t s ofR a d i a t i o n on M a t e r i a l s ( R e i n h o l d , N e w Y o r k ,1 9 5 8 ) .D . S . B i l l i n g t o n and J . H . C r a w f o r d , Jr,R a d i a t i o n D a m a g e in S o l i d s ( P r i n c e t o nU n i v e r s i t y P r e s s , 1 9 6 1 ) .F . S e i t z and J . S . K o e h l e r , S o l i d S t a t eP h y s i c s 2 ( A c a d e m i c P r e s s , N e w Y o r k , 1 9 5 5 ) .J . W . M a y e r and O . J . M a r s h in A p p l i e d S o l i dS t a t e S c i e n c e , C . J . K r i e s s m a n and R . W o l f ,eds ( A c a d e m i c P r e s s , N e w Y o r k , 1 9 6 8 ) .D . J . M a z e y , R . S . N e l s o n and R o S . B a r n e s , P h i l .Mag. 17, 223 ( 1 9 6 8 ) .T . W a d a , N u c l . I n s t r . and M e t h . 1 8 2 / 1 8 3 ,131 ( 1 9 8 1 ) .T . W a d a , P r o c . 3rd I n t e r n . C o n f . on N e u t r o n -T r a n s m u t a t i o n D o p e d Si ( P l e n u m P r e s s , N e wY o r k and L o n d o n ) , 447 ( 1 9 8 1 ) .T . W a d a and M . K a n e i w a , I n s t . P h y s . C o n f .Ser. 59 223 ( 1 9 8 1 ) .T . W a d a , M . T a k e d a , K . Y a s u d a and H . M a s u d a ,P r o c . 6th S y m p . on Ion S o u r c e s and Ion-A s s i s t e d T e c h n o l o g y ( I o n i c s Co, T o k y o ) , 433( 1 9 8 2 ) .T . W a d a , K . N a k a i and H . H a d a , P r o c . 4thI n t e r n . C o n f . on Ion I m p l a n t a t i o n ,E q u i p m e n t and T e c h n i q u e s ( S p r i n g e r - V e r l a g ,B e r l i n , H e i d e l b e r g , N e w Y o r k and T o k y o ) ii,214 ( 1 9 8 3 ) .T . W a d a and M . T a k e d a , P r o c . I n t e r n . IonE n g i n e e r i n g C o n g r e s s ( I o n i c s Co, T o k y o ) .


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electron-beam doping-electron radiation effects in impurity overlayers and semiconductor substrates

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