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PULSED LASER AND ELECTRON BEAM INDUCED
DIFFUSION OF ANTIMONY IN SILICON
E. Fogarassy, P. Siffert, Damien Barbier, G. Chemisky, A. Laugier
To cite this version:
PULSED LASER
ANDELECTRON BEAM INDUCED DIFFUSION OF ANTIMONY IN SILICON
E. Fogarassy, P. Siffert, D. ~ a r b i e r * , G. chemisky* and A. ~ a u ~ i e r * Centre de Recherches Nucle'aires, Laboratoire PHASE, 67037 Strasbourg Cedex, France
'TNSA, 69622 V i Z leurbanne Cedex, France
Resume
-
Le
b u tde ce t r a v a i l e s t de comparer l a diffusion i n d u i t e , s o i t par
une impulsion l a s e r , s o i t a r un faisceau d ' e l e c t r o n s pulses, d'un film mince
li
d'antimoine d'environ 100
d16paisseur dans un s u b s t r a t c r i s t a l l i n de s i l i -
cium. Les resul t a t s dedui t s d ' experiences de retrodiffusion de particul es
chargees (RBS), sont i n t e r p r e t & en u t i l i s a n t l e s profil
de d i s t r i b u t i o n
des temperatures dans l e s zones t r a i t e e s , obtenus en resolvant ll@quation
de l a chaleur pour chacune des deux techniques de r e c u i t ( l a s e r e t e l e c t r o n s ) .
Abstract
-
The aim of t h i s work i s t o compare the diffusion into s i l i c o n of
a thin film
(% 100a)
of deposited antimony induced e i t h e r
bya pulsed l a s e r
i r r a d i a t i o n or electron beam and t o i n t e r p r e t the d i f f e r e n t experimental beha-
viours as observed by Rutherford backscattering spectrometry, by using the
calculated temperature d i s t r i b u t i o n s obtained by solving the heat flow equa-
tion f o r the two d i f f e r e n t annealing processes.
INTRODUCTION
I t has been demonstrated i n previous works, t h a t pulsed l a s e r
1.1,
2 1 or electron
beams 131 can be used t o introduce i n t o the s i l i c o n l a t t i c e dopants deposited on
the surface t h a t diffuse rapidly i n the melted layer. The purpose of t h i s study
i s t o compare, by Rutherford backscattering spectrometry (RBS), the d i s t r i b u t i o n
of antimony i n s i l i c o n , i t s incorporation in substitutional s i t e s , and the disorder
produced near the surface by using these two d i f f e r e n t types of localized heating
source. The experimental r e s u l t s have been interpreted on the basis of the thermal
models obtained, by solving the heat flow equations, respectively f o r t h e pulsed
l a s e r and electron beam processing.
EXPERIMENT
Thin films of high purity antimony have been deposited by vacuum evaporation
( p
-
lo-%orr), on monocristall ine
si
1 icon substrates of < I l l > orientation. The
thickness of the deposited layers i n the range of 100 t o 120
A ,has been measured
by using the quartz monitor. The amount of dopant deposited, as deduced from RBS
experiments ranged from
3 . 3x
1016
and
3 . 7x
1016 cm-'.
The r e s u l t s given by the experimental procedures have been found t o be i n good
agreement.
The samples covered with the dopant film have been i r r ~ a d i a t e d
with a pulsed l a s e r
o r electron beams under the following conditions
:-5
-
The l a s e r treatment has been performed e i t h e r in a i r o r under vacuum (p
%10
t o r r ) using the amplified monomode out p u t of a 20 ns duration pulsed ruby l a s e r ,
emitting energy d e n s i t i e s in the range
1t o
2~ l c m z ;
-
Electron beam pulses of 50
ns
i n duration were used with two d i f f e r e n t electron
spectral energy d i s t r i b u t i o n s refered a s type a (mean electron energy E
=12 KeV)
C5-242 JOURNAL DE PHYSIQUE
2 and type b
(E
= 16 KeV).
The energy d e n s i t i e s were i n t h e 0.8-
1.5 J/cm range. I n a l l cases, t h e evaporation losses of antimony d u r i n g i r r a d i a t i o n as measured by RBS, have been found l e s s than 15% o f t h e i n i t i a l amount o f deposited dopant. The d i s t r i b u t i o n p r o f i l e s of both t o t a l and s u b s t i t u t i o n a l dopant were determined by RBS measurements performed under random and channeling c o n d i t i o n s w i t h a 4 ~ e + i o n beam o f 1-
2 MeV energy. The backscattered p a r t i c l e s were detected by means o f a surface b a r r i e r d e t e c t o r . T h i s arrangement g i v e s an e q u i v a l e n t depth0 r e s o l u t i o n o f about 200 A f o r S i . RESULTS 0 F i g u r e I r e p o r t s t h e r e s u l t s obtained f o r a 120 A Sb f i l m on S i a f t e r l a s e r i r r a d i a t i o n , i n a i r , a t E = 1.45 ~/cmZ. The dopant p r o f i l e m a i n l y c o n s i s t s of
-.
an i n - d e p t h d i s t r i b u t i o n , w i t h a h i g h l y s u b s t i t u t i o n a l Sb c o n c e n t r a t i o n o f 1.2x10L1 C ~ I I - ~ . C ~ O S ~ t o t h e s o l u b i l i t y l i m i t achieved by l a s e r annealing ( t S 4 . 3 x i 0 ~ ~ c d 3 } / 4 1and l a r g e l y i n excess o f t h e thermal e q u i l i b r i u m s o l u b i l i t y (C; s 6x1019 cm-3 a t T = 1200°C).
The f r a c t i o n o f t h e i n i t i a l l y deposited Sb atoms, which has d i f f u s e d i n depth i n t o t h e substrate, i s i n the o r d e r o f 80%. About 50% o f t h i s f r a c t i o n i s incorpo- r a t e d i n s u b s t i t u t i o n a l s i t e s i n t o the s i l i c o n l a t t i c e . A s i m i l a r behaviour i s observed f o r l a s e r treatments performed under vacuum.
0
F i g . 1
-
Random and a l i g n e d RBS spectra o f a 120 A Sb f i l m deposited on S i < I l l > and i r r a d i a t e d w i t h a ruby l a s e r p u l s e (1.45 ~ / c m ~ )- Random
. _ - Aligned 2) ~ f t e r rn
etching
0
-
1000 500 0 2000 I000 0 0 DEPTH (A) F i g . 2
-
Random and a l i g n e d RBS s p e c t r a o f a 100 A Sb f i l m d e p o s i t e don S i < I l l > and i r r a d i a t e d w i t h an e l e c t r o n beam p u l s e (1.3 J/cm )
1) b e f o r e t e c h i n g 2) a f t e r e t c h i n g
mum s u b s t i t u t i o n a l c o n c e n t r a t i o n (% 6.5 x
l o z 0
cmm3) has been deduced from c h a n n e l i n ge x p - r i m e n t s ( F i g . 2.2) performed a f t e r e t c h i n g o f t h e d i s o r d e r e d Sb s u r f a c e l a y e r which c o n t a i n s a b o u t 75% o f t h e i n i t i a l d e p o s i t e d Sb atoms. A s i m i l a r b e h a v i o u r i s o b t a i n e d w i t h t y p e a e l e c t r o n beam p u l s e d a t 1.0 ~ / c m 2 .
INTERPRETATION OF THESE RESULTS
C o n s i d e r i n g a s t r i c t l y thermal approach, we can assume t h a t t h e energy i s f u l l y t r a n s f e r e d t o t h e s i l i c o n l a t t i c e l e a d i n g t o s u p e r f i c i a l m e l t i n g . D u r i n g t h i s m e l t i n g
2
process, d i f f u s i o n i n l i q u i d phase (DL % cm / s e c . ) ( 5 ) o c c u r s f r o m t h e s u r f a c e
as w e l l e s t a b l i s h e d now i n t h e l i t e r a t u r e . D u r i n g t h e e p i t a x i a l r e g r o w t h t h e m e l t f r o n t v e l o c i t i e s , as deduced f r o m h e a t f l o w c a l c u l a t i o n s (6, 7), a r e r e s p e c t i v e l y 3 m/s f o r t h e l a s e r process and 2 m/s f o r t h e e l e c t r o n beam process ( t y p e a and b) F o r t h e s e v a l u e s , t h e i n t e r f a c i a l s e g r e g a t i o n c o e f f i c i e n t K = Cs
/
CL a r e muchh i g h e r than t h e thermal e q u i l i b r i u m s e g r e g a t i o n c o e f f i c i e n t (KO = 0.023 f o r a n t i m o n y ) . As shown i n a p r e v i o u s work ( 8 ) , t h e l i n e a r r e l a t i o n :
0 K
C = C x - a l l o w s t o deduce t h e v a l u e o f k From t h e measured v a l u e o f s s
KO
Cs (a1 1 symbols have-the same meaning as i n Ref. 8 )
.
The r e s u l t s a r e k % 0.25 f o rC5-244 JOURNAL DE PHYSIQUE
On F i g u r e 3, we have compared t h e enthalpy d i s t r i b u t i o n i n the i r r a d i a t e d l a y e r f o r t h e two d i f f e r e n t h e a t i n g processes, F i r s t , one can see, i n the case o f t h e l a s e r beam, t h a t t h e l a t e n t heat i s exceeded a l l over t h e m e l t i n g l a y e r . By c o n t r a s t , on t h e same Figure, i t appears t h a t t h i s behaviour i s d i f f e r e n t f o r t h e e l e c t r o n beam, because o f a more p e n e t r a t i n g energy d e p o s i t i o n p r o f i l e , which depends on t h e e l e c t r o n energy d i s t r i b u t i o n . The l e s s p e n e t r a t i n g e l e c t r o n beam p u l s e ( t y p e a) induces t h e deepest f u l l y molten zone. According t o t h i s p a r t i c u l a r f e a t u r e , t h e i n c o r p o r a t i o n o f s u b s t i t u t i o n a l Sb i s l e s s probable i n t h e m e l t i n g zone by comparison w i t h a f u l l y molten zone as observed on F i g . 2, corresponding t o type b e l e c t r o n beam processing.
- - -
-
-
-FULLY MELT LIMIT-.
I- . - _
0
1
2
3
4
5
DEPTH
(mi
c r o n s )
F i g . 3-
C a l c u l a t e d enthalpy d i s t r i b u t i o n p r o f i l e s i n l a s e r and e l e c t r o n beam t r e a t e d samples.I n o r d e r t o c o n f i r m t h i s model we have used t h e two types o f e l e c t r o n beams pre- v i o u s l y described. The corresponding d i s t r i b u t i o n p r o f i l e s , as deduced from RBS experiments ( F i g . 4 f o r type a and 5 f o r type b ) show a considerably l a r g e r e x t e n t o f Sb atoms i n the case o f the l e s s p e n e t r a t i n g e l e c t r o n ( t y p e a) h e a t i n g procedure.
CONCLUSION
s u r f a c e d i s o r d e r e d 1E21
-
m E 0-
l a y e r Energy d e n s i t y : t O.BJ/cm2 t x i.OJ/cm2 I I , , ,1
Energy d e n s i t y : t \ X s u r f a c e d i s o r d e r e d l a y e r F i g . 4-
Random RBS s p e c t r a o f a 100 A F i g . 5-
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