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Segregation of impurities due to pulsed laser beam annealing
Nuclear Instruments and Methods 199 (1982) 397-400 North-Holland Publishing C o m p a n y
397
S E G R E G A T I O N OF I M P U R I T I E S DUE T O P U L S E D LASER BEAM ANNEALING I.B. K H A I B U L L I N , E.I. SHTYRKOV, R.M. BAYAZITOV and R.A. A G A N O V Kazan Physico-Technical Institute, Kazan, USSR
T. LOHNER, G. MEZEY, F. P,~SZTI, A. MANUABA, E. K()TAI and J. G Y U L A I Central Research Institute for Physics, H-1525 Budapest 114, PO Box 49, Hungary
A simple theory of the redistribution and segregation of the solutes which occur during the solidification after pulsed laser beam annealing is presented. For experimental verification, the laser processing of Bi ÷ implants at different doses was investigated by backscattering spectroscopy and a qualitative agreement between the experimental and calculated values was found.
1. Introduction ~ Ce The mechanism of regrowth and dopant redistribution during pulsed laser beam annealing (PLBA) has been extensively studied. Strong accumulation at or near the surface was investigated as a function of regrowth velocity [1] and crystal orientation [2] for dopants of the I I I - V elements of the periodic system. This paper investigates the segregation of dopants taking into account the initial concentration of the solute. An extension of calculations of Smith et al. [3] with the relation between diffusion coefficient (D) and equilibrium segregation coefficient (k0) published by Shashkov and Gurevich [4] leads to a good correlation between surface accumulation and segregation. The calculations are in qualitative agreement with experimental data of both the present work and that of Hoonhout and Saris [5] for other dopants.
2. Theoretical background Let us consider a system with CO equilibrium concentration before laser irradiation. At the onset of irradiation, k 0 is equal to C s / C L , where Cs and C L are concentrations in the solid and liquid phase respectively. According to ref. 3, at the beginning of phase transformation, the impurity concentration in the solid phase [in depth interval (x0,x2) ] can be written as: R Cs = C o i l - - ( 1 - - k o ) e x p ( - k o - - ~ x ) ] ,
. . . . C T:.:...'I . . . . .....'"!\
t--z LLI
:. : ."
.
I\ ~-~ I I \\
I \ ~ \ I \ I \
. . . . . . Ii....'-~. (..) I
KoC~ 7,o=0 X1
SURFACE
~\
D/R "-.
INTERFACE
I
X2
~ LIQUID X3 X~d
Fig. l. Schematic picture of solidification. C O is the equilibrium concentration of dopant before laser irradiation, k 0 the equilibrium segregation coefficient, C s and C L the concentration in the solid and liquid phases, C x the interface concentration in the transient stage, D the diffusion coefficient, R the regrowth velocity.
where D is the diffusion coefficient of impurity and R is the rate of movement of the interface (fig. 1). During this transient stage, the interface concentration in the liquid phase CT(X ) quickly reaches a saturation value, which is the eutectic concentration (at the point x - - x 2 ) . Beyond this point, further increase of CT(X) is prohibited, because no additional temperature rise can be expected in the liquid phase. At x > x 2, the impurity concentration in the solid phase proceeds to a stationary value, Cs ~ Co, and the concentration ratio will be C s / C L = C o / C e = k ' at the solid interface. In the stationary state, the impurity concentration in the melt [3] is:
(1)
0167-5087/82/0000-0000/$02.75 © 1982 North-Holland
Co[, VII. R A D I A T I O N EFFECTS
1. B. Khaibulhn et al. / Segregation of impurities
398
where x ' is the distance from the solid-liquid interface. The quantity of accumulated impurity at the surface ( N ) can be determined by integrating eq. (1) or eq. (2) over the melted layer of thickness
d ( d>>D/R ) 1 - k o D [l _exp(_koR d ) ] N=C° ko R if Gr(d) < C~, 1-k'
N=C° k'
D
R
(3)
lations. (The following values were used: d = 2 × 10-5 cm, R • 200 c m / s , [5] % : 5 × 10 20 c m 3 ce : 5 × 1 0 2 2 c m 3). The correlation between experiment and calculation is satisfactory, i.e. the surface fraction of the impurity versus k o curve has a slight maximum.
3. Experimental
ifCv(d)>~Ce.
According to ref. 4 it was taken into account that the diffusion coefficient depends on the equilibrium segregation coefficient. This dependence can be formulated as D = 3 × l0 4k~;/3(cm2/s) in the range of k 0 = l0 4-1. The relationship, which was determined experimentally, gives more realistic values than that of the generally accepted work [6]. Eq. (3) shows that the surface fraction is determined by the height and width of the concentration peak at the solid-liquid interface. This indicates that for a high rate of movement of the interface R ~ 6 m / s at PLBA, the impurity atoms are not able to diffuse into a deeper region of the melt [2], so the width of the concentration peak is only 1---50 nm. In the case of materials characterized by small segregation coefficients, this width decreases through the diffusion coefficient. Through the limiting role of Ce for C l....... it is reasonable that the smaller the segregation coefficient, the smaller accumulation that can be expected. Table 1 compares the experimental values of Hoonhout and Saris with the present calcu-
To study the depth distribution of implanted atoms and their profile-modification during PLBA, 80 keV Bi + was implanted into chemically etched Si of (111) orientation at room temperature in the dose range of 1014- 1016 a t o m s / c m 2. After implantation all the samples were subjected to laser annealing which was performed in open air with a single ruby laser pulse of 15 ns duration. The applied energy density was 1.25 J / c m 2 which was sufficient to induce complete epitaxial regrowth of the implanted layer The samples were analysed with backscattering spectrometry (BS) of 5 nm resolution using glancing detection. This way the surface fraction of Bi within the first 10 nm film could easily be measured.
4. Results and discussion The verification of this simple theory was done by BS investigation of specimens implanted by different doses of Bi after PLBA. Fig. 2 shows the random spectra in the lowest dose case. The high
'Fable 1 Comparison of the measured and the calculated surface fraction of dopants in silicon after PLBA Dopant atom
Ge As Sb Sn Ga Bi Te Se
Equilibrium segregation coefficient [8]
The number of the dopant atoms in the first 23 nm of the surface Measured values, Hoonhout et al. [5] (%)
Calculated values, present work (%)
0.33 0.30 2.3×10 z 1.6×10 2 8.0×10 3 7.0×10 4 8.0×10 6 10 8
11 14 10 28 55 I1 11 8.5
10 12 60 67 78 67 15 1.6
1. B. Khaibullin et al. / Segregation of impurities 80 key Bi ÷ in
<111> St,
ANALYSIS ; 1,2 MeV
8OkeV
DOSE =2.5 xlO 1~" a t o m s l c m 2
Bi*
in
399
<111>
ANALYSIS : 12MeV
aHe*
D O S E - G x l O 1~ a t o m s / c m 2
Si,
4He*
AS-IMPLANTED
•
• AS-IMPLANTED
• LASER
ANNEALED
* LASER ANNEALED
1500:
1500
(Q SWITCHED
( O - SWITCHED .~ . , ~ . . ,. , *
DEPTH
*
[~,]
SOD I000
t
' '
.
RUBY LASER
o
~
"
•
DEPTH [~,]
' '~J
0 , 9 6 . 1.12 JOULE/cm 2 )
c3 Ld
01000
•
9 500
.......
•
500
150
200
250 300 CHANNEL NUMBER
ENERGY
in
4He ÷
• AS IMPLANTED
DEPTH[~,I 500 . . . .
O7
c~ uJ
t
-
~t
•
.
.
.
150 ~4
06
.
80 keV
O ,
200
68
112
-
[MeV]
in <111> Si, 12 MeV
DOSE- 6x10 u" a t o m s l c m 2 •
Z'He*
AS-IMPLANTED
[~]
DEPTH
LO£O. ~oo
1500
• LASER
<111>
RUBY LASER •
.-,,
DEPTH [A]
z
500
E=15 nsec
.0
200125
JOULE/cm 2)
1000
c) Lu >
500
4 150
I(30 04
al
200 250 300 CHANNEL NUMBER
06
08
(O ~2 ENERGY [MeV]
-
Fig. 5. Channeling spectra of silicon implanted by 6X1014 B i / c m 2. 80 keY
Bi ~ in
ANALYSIS
<111> $1,
12 MeV
D O S E - lx1016
otoms/cm 2
Z'He* •
<111>
1000
500
........
AS-IMPLANTED
* LASER ANNEALED 0 (Q -SWITCHED
RUBY LASER 1000~
~C = 15 nsec )
1~ J~
J
: -- 500 "!
"
"~
":"
,
i
250
ANNEALED
( Q-SWITCHED
0
DEPTH [/~]
!6o F
I
<111>
• VIRGIN <111>
<111)
0.96 + 112 JOULE/cm 2 )
[40
',~4~,~¢~_~Z:
.
Bi"
ANALYSIS
i~= 15 nsec
DEPTH [A] 500
-
500'
300
NUMBER
RUBY LASER
........
:
250
~b
Fig. 4. R a n d o m spectra of silicon implanted by 6 × 1014 B i / c m 2. The surface accumulation after P L B A is 27%.
(Q-SWITCHED
O ~ ~ I:~I
~ 100o
b-~
JOULE/cm 2 )
/.-~. 1po~_
d11)
4- LASER ANNEALED 0 i
•
C
200
o°6
125
lOO
ENERGY
• VIRGIN 1000
150
-0:4
(111> S,, D O S E - 2 . 5 x l 0 u" a t o m s / c m 2
ANALYSIS 12 MeV
1500
~oo "
[MeV]
regrowth velocity produced a surface accumulation of 31% of the total amount of impurity and a flat profile in the deeper region of the surface. The channeling spectra in fig. 3 show a complete recrystallization of silicon, highly substitutional Bi profile in the deeper region and no lattice location in the surface peak. For higher doses (figs. 4-7) the relative number of Bi atoms in the surface peak decreases• These values are summarized in table 2. This tendency is in accordance with present calculation i.e. the higher the dose, the fewer atoms accumulate in the surface layer because of the limiting factor of the eutectic concentration and low diffusion coefficient together.
Bi*
LASER
!,6o
.
CHANNEL
Fig. 2. R a n d o m spectra of both the as-implanted and laser annealed sample at the dose of 2.5 × l014 B i / c m ~.
80 keY
200
~
_
.
100
RUBY
....
.o
300
~
ib ~2 ENERGY [MeV]
Fig. 3. Channeling spectra of the lowest dose of both the a s - i m p l a n t e d and laser annealed sample.
~OO
150
200
250
300
CHANNEL NUMBER ENERGY
[MeV]
Fig. 6. R a n d o m spectra of silicon implanted with l X 10 t6 B i / c m 2. The surface accumulation is 19%. VII. R A D I A T I O N E F F E C T S
I.B. Khaibullin et al. / Segregation of impurities
400 80
keV Bi + in
ANALYSIS 1.2 MeV
<111> Si,
DOSE-1A-IO 16 a t o m s / c m 2
~He+ • AS IMPLANTED
DEPTH [~]
tODD 4
5oo
o
* LASER ANNEALED
",,
(Q - SWITCHED RUBY LASER ~" =15 nsec 112 JOULE/cm 2)
In conclusion, the present paper suggests a simple model by which a qualitative agreement can be achieved between the measured and calculated surface fractions of dopants at or near the surface because earlier approaches [5,7] failed to describe the experimental findings and the concept of thermal melting during PLBA was doubted.
4OO Ld
References
2OO i
100
150
200
06
08
04
250 300 CHANNEL NUMBER
11] ENERGY [MeV]
12
Fig. 7. R a n d o m spectra of silicon implanted with l A X 1016 B i / c m 2. The surface accumulation is 12%.
Table 2 Measured and calculated surface fraction of Bi atoms which was found in the first 10 n m of the surface after PLBA. For calculation R = 6 0 0 c m / s [1], d = 3 x 10 -5 cm [9], k 0 = 7 X 10 4 [8] and ce = 5 x 10 zz a t o m s / c m 3 values were used Implanted dose ( a t o m s / c m 2)
2.5 X 1014 6X 1014 1X 1016 1.2X 1016
1.4X 1016
The number of the Bi atoms in the first 10 n m of the surface Measured by BS
Calculated
(%)
(%)
31 27 19 16 12
80 80 22 18 16
[1] P. Baeri, J.M. Poate, S.V. Campisano, G. Foti, E. Rimini and A.G. Cullis, Appl. Phys. Lett. 37 (1980) 912. [2] P. Baeri, G. Foti, J.M. Poate, S.V. Campisano and A.G. Cullis, Appl. Phys. Lett. 38 (1981) 800. [3] V.G. Smith, W.A. Tiller and J.W. Rutter, Can. J. Phys. 33 (1955) 723. [4] Yu.M. Shashkov and V.M. Gurevich, J. Phys. Chem. 42 (1968) 2058 (in Russian). [5] D. Hoonhout and F.W. Saris, Phys. Lett. 74A (1979) 253. [6] H. Kodera, Jpn. J. Appl. Phys. 2 (1963) 212. [7] P. Baeri, S.U. Campisano, G. Foti and E. Rimini, Phys. Rev. Lett. 41 (1978) 1246. [8] F.A. Trumbore, The Bell System Techn. Journal, January (1960) 2O5. [9] P. Baeri, S.U. Campisano, G. Foti and E. Rimini. J. Appl. Phys. 50 (1979) 788.
397
S E G R E G A T I O N OF I M P U R I T I E S DUE T O P U L S E D LASER BEAM ANNEALING I.B. K H A I B U L L I N , E.I. SHTYRKOV, R.M. BAYAZITOV and R.A. A G A N O V Kazan Physico-Technical Institute, Kazan, USSR
T. LOHNER, G. MEZEY, F. P,~SZTI, A. MANUABA, E. K()TAI and J. G Y U L A I Central Research Institute for Physics, H-1525 Budapest 114, PO Box 49, Hungary
A simple theory of the redistribution and segregation of the solutes which occur during the solidification after pulsed laser beam annealing is presented. For experimental verification, the laser processing of Bi ÷ implants at different doses was investigated by backscattering spectroscopy and a qualitative agreement between the experimental and calculated values was found.
1. Introduction ~ Ce The mechanism of regrowth and dopant redistribution during pulsed laser beam annealing (PLBA) has been extensively studied. Strong accumulation at or near the surface was investigated as a function of regrowth velocity [1] and crystal orientation [2] for dopants of the I I I - V elements of the periodic system. This paper investigates the segregation of dopants taking into account the initial concentration of the solute. An extension of calculations of Smith et al. [3] with the relation between diffusion coefficient (D) and equilibrium segregation coefficient (k0) published by Shashkov and Gurevich [4] leads to a good correlation between surface accumulation and segregation. The calculations are in qualitative agreement with experimental data of both the present work and that of Hoonhout and Saris [5] for other dopants.
2. Theoretical background Let us consider a system with CO equilibrium concentration before laser irradiation. At the onset of irradiation, k 0 is equal to C s / C L , where Cs and C L are concentrations in the solid and liquid phase respectively. According to ref. 3, at the beginning of phase transformation, the impurity concentration in the solid phase [in depth interval (x0,x2) ] can be written as: R Cs = C o i l - - ( 1 - - k o ) e x p ( - k o - - ~ x ) ] ,
. . . . C T:.:...'I . . . . .....'"!\
t--z LLI
:. : ."
.
I\ ~-~ I I \\
I \ ~ \ I \ I \
. . . . . . Ii....'-~. (..) I
KoC~ 7,o=0 X1
SURFACE
~\
D/R "-.
INTERFACE
I
X2
~ LIQUID X3 X~d
Fig. l. Schematic picture of solidification. C O is the equilibrium concentration of dopant before laser irradiation, k 0 the equilibrium segregation coefficient, C s and C L the concentration in the solid and liquid phases, C x the interface concentration in the transient stage, D the diffusion coefficient, R the regrowth velocity.
where D is the diffusion coefficient of impurity and R is the rate of movement of the interface (fig. 1). During this transient stage, the interface concentration in the liquid phase CT(X ) quickly reaches a saturation value, which is the eutectic concentration (at the point x - - x 2 ) . Beyond this point, further increase of CT(X) is prohibited, because no additional temperature rise can be expected in the liquid phase. At x > x 2, the impurity concentration in the solid phase proceeds to a stationary value, Cs ~ Co, and the concentration ratio will be C s / C L = C o / C e = k ' at the solid interface. In the stationary state, the impurity concentration in the melt [3] is:
(1)
0167-5087/82/0000-0000/$02.75 © 1982 North-Holland
Co[, VII. R A D I A T I O N EFFECTS
1. B. Khaibulhn et al. / Segregation of impurities
398
where x ' is the distance from the solid-liquid interface. The quantity of accumulated impurity at the surface ( N ) can be determined by integrating eq. (1) or eq. (2) over the melted layer of thickness
d ( d>>D/R ) 1 - k o D [l _exp(_koR d ) ] N=C° ko R if Gr(d) < C~, 1-k'
N=C° k'
D
R
(3)
lations. (The following values were used: d = 2 × 10-5 cm, R • 200 c m / s , [5] % : 5 × 10 20 c m 3 ce : 5 × 1 0 2 2 c m 3). The correlation between experiment and calculation is satisfactory, i.e. the surface fraction of the impurity versus k o curve has a slight maximum.
3. Experimental
ifCv(d)>~Ce.
According to ref. 4 it was taken into account that the diffusion coefficient depends on the equilibrium segregation coefficient. This dependence can be formulated as D = 3 × l0 4k~;/3(cm2/s) in the range of k 0 = l0 4-1. The relationship, which was determined experimentally, gives more realistic values than that of the generally accepted work [6]. Eq. (3) shows that the surface fraction is determined by the height and width of the concentration peak at the solid-liquid interface. This indicates that for a high rate of movement of the interface R ~ 6 m / s at PLBA, the impurity atoms are not able to diffuse into a deeper region of the melt [2], so the width of the concentration peak is only 1---50 nm. In the case of materials characterized by small segregation coefficients, this width decreases through the diffusion coefficient. Through the limiting role of Ce for C l....... it is reasonable that the smaller the segregation coefficient, the smaller accumulation that can be expected. Table 1 compares the experimental values of Hoonhout and Saris with the present calcu-
To study the depth distribution of implanted atoms and their profile-modification during PLBA, 80 keV Bi + was implanted into chemically etched Si of (111) orientation at room temperature in the dose range of 1014- 1016 a t o m s / c m 2. After implantation all the samples were subjected to laser annealing which was performed in open air with a single ruby laser pulse of 15 ns duration. The applied energy density was 1.25 J / c m 2 which was sufficient to induce complete epitaxial regrowth of the implanted layer The samples were analysed with backscattering spectrometry (BS) of 5 nm resolution using glancing detection. This way the surface fraction of Bi within the first 10 nm film could easily be measured.
4. Results and discussion The verification of this simple theory was done by BS investigation of specimens implanted by different doses of Bi after PLBA. Fig. 2 shows the random spectra in the lowest dose case. The high
'Fable 1 Comparison of the measured and the calculated surface fraction of dopants in silicon after PLBA Dopant atom
Ge As Sb Sn Ga Bi Te Se
Equilibrium segregation coefficient [8]
The number of the dopant atoms in the first 23 nm of the surface Measured values, Hoonhout et al. [5] (%)
Calculated values, present work (%)
0.33 0.30 2.3×10 z 1.6×10 2 8.0×10 3 7.0×10 4 8.0×10 6 10 8
11 14 10 28 55 I1 11 8.5
10 12 60 67 78 67 15 1.6
1. B. Khaibullin et al. / Segregation of impurities 80 key Bi ÷ in
<111> St,
ANALYSIS ; 1,2 MeV
8OkeV
DOSE =2.5 xlO 1~" a t o m s l c m 2
Bi*
in
399
<111>
ANALYSIS : 12MeV
aHe*
D O S E - G x l O 1~ a t o m s / c m 2
Si,
4He*
AS-IMPLANTED
•
• AS-IMPLANTED
• LASER
ANNEALED
* LASER ANNEALED
1500:
1500
(Q SWITCHED
( O - SWITCHED .~ . , ~ . . ,. , *
DEPTH
*
[~,]
SOD I000
t
' '
.
RUBY LASER
o
~
"
•
DEPTH [~,]
' '~J
0 , 9 6 . 1.12 JOULE/cm 2 )
c3 Ld
01000
•
9 500
.......
•
500
150
200
250 300 CHANNEL NUMBER
ENERGY
in
4He ÷
• AS IMPLANTED
DEPTH[~,I 500 . . . .
O7
c~ uJ
t
-
~t
•
.
.
.
150 ~4
06
.
80 keV
O ,
200
68
112
-
[MeV]
in <111> Si, 12 MeV
DOSE- 6x10 u" a t o m s l c m 2 •
Z'He*
AS-IMPLANTED
[~]
DEPTH
LO£O. ~oo
1500
• LASER
<111>
RUBY LASER •
.-,,
DEPTH [A]
z
500
E=15 nsec
.0
200125
JOULE/cm 2)
1000
c) Lu >
500
4 150
I(30 04
al
200 250 300 CHANNEL NUMBER
06
08
(O ~2 ENERGY [MeV]
-
Fig. 5. Channeling spectra of silicon implanted by 6X1014 B i / c m 2. 80 keY
Bi ~ in
ANALYSIS
<111> $1,
12 MeV
D O S E - lx1016
otoms/cm 2
Z'He* •
<111>
1000
500
........
AS-IMPLANTED
* LASER ANNEALED 0 (Q -SWITCHED
RUBY LASER 1000~
~C = 15 nsec )
1~ J~
J
: -- 500 "!
"
"~
":"
,
i
250
ANNEALED
( Q-SWITCHED
0
DEPTH [/~]
!6o F
I
<111>
• VIRGIN <111>
<111)
0.96 + 112 JOULE/cm 2 )
[40
',~4~,~¢~_~Z:
.
Bi"
ANALYSIS
i~= 15 nsec
DEPTH [A] 500
-
500'
300
NUMBER
RUBY LASER
........
:
250
~b
Fig. 4. R a n d o m spectra of silicon implanted by 6 × 1014 B i / c m 2. The surface accumulation after P L B A is 27%.
(Q-SWITCHED
O ~ ~ I:~I
~ 100o
b-~
JOULE/cm 2 )
/.-~. 1po~_
d11)
4- LASER ANNEALED 0 i
•
C
200
o°6
125
lOO
ENERGY
• VIRGIN 1000
150
-0:4
(111> S,, D O S E - 2 . 5 x l 0 u" a t o m s / c m 2
ANALYSIS 12 MeV
1500
~oo "
[MeV]
regrowth velocity produced a surface accumulation of 31% of the total amount of impurity and a flat profile in the deeper region of the surface. The channeling spectra in fig. 3 show a complete recrystallization of silicon, highly substitutional Bi profile in the deeper region and no lattice location in the surface peak. For higher doses (figs. 4-7) the relative number of Bi atoms in the surface peak decreases• These values are summarized in table 2. This tendency is in accordance with present calculation i.e. the higher the dose, the fewer atoms accumulate in the surface layer because of the limiting factor of the eutectic concentration and low diffusion coefficient together.
Bi*
LASER
!,6o
.
CHANNEL
Fig. 2. R a n d o m spectra of both the as-implanted and laser annealed sample at the dose of 2.5 × l014 B i / c m ~.
80 keY
200
~
_
.
100
RUBY
....
.o
300
~
ib ~2 ENERGY [MeV]
Fig. 3. Channeling spectra of the lowest dose of both the a s - i m p l a n t e d and laser annealed sample.
~OO
150
200
250
300
CHANNEL NUMBER ENERGY
[MeV]
Fig. 6. R a n d o m spectra of silicon implanted with l X 10 t6 B i / c m 2. The surface accumulation is 19%. VII. R A D I A T I O N E F F E C T S
I.B. Khaibullin et al. / Segregation of impurities
400 80
keV Bi + in
ANALYSIS 1.2 MeV
<111> Si,
DOSE-1A-IO 16 a t o m s / c m 2
~He+ • AS IMPLANTED
DEPTH [~]
tODD 4
5oo
o
* LASER ANNEALED
",,
(Q - SWITCHED RUBY LASER ~" =15 nsec 112 JOULE/cm 2)
In conclusion, the present paper suggests a simple model by which a qualitative agreement can be achieved between the measured and calculated surface fractions of dopants at or near the surface because earlier approaches [5,7] failed to describe the experimental findings and the concept of thermal melting during PLBA was doubted.
4OO Ld
References
2OO i
100
150
200
06
08
04
250 300 CHANNEL NUMBER
11] ENERGY [MeV]
12
Fig. 7. R a n d o m spectra of silicon implanted with l A X 1016 B i / c m 2. The surface accumulation is 12%.
Table 2 Measured and calculated surface fraction of Bi atoms which was found in the first 10 n m of the surface after PLBA. For calculation R = 6 0 0 c m / s [1], d = 3 x 10 -5 cm [9], k 0 = 7 X 10 4 [8] and ce = 5 x 10 zz a t o m s / c m 3 values were used Implanted dose ( a t o m s / c m 2)
2.5 X 1014 6X 1014 1X 1016 1.2X 1016
1.4X 1016
The number of the Bi atoms in the first 10 n m of the surface Measured by BS
Calculated
(%)
(%)
31 27 19 16 12
80 80 22 18 16
[1] P. Baeri, J.M. Poate, S.V. Campisano, G. Foti, E. Rimini and A.G. Cullis, Appl. Phys. Lett. 37 (1980) 912. [2] P. Baeri, G. Foti, J.M. Poate, S.V. Campisano and A.G. Cullis, Appl. Phys. Lett. 38 (1981) 800. [3] V.G. Smith, W.A. Tiller and J.W. Rutter, Can. J. Phys. 33 (1955) 723. [4] Yu.M. Shashkov and V.M. Gurevich, J. Phys. Chem. 42 (1968) 2058 (in Russian). [5] D. Hoonhout and F.W. Saris, Phys. Lett. 74A (1979) 253. [6] H. Kodera, Jpn. J. Appl. Phys. 2 (1963) 212. [7] P. Baeri, S.U. Campisano, G. Foti and E. Rimini, Phys. Rev. Lett. 41 (1978) 1246. [8] F.A. Trumbore, The Bell System Techn. Journal, January (1960) 2O5. [9] P. Baeri, S.U. Campisano, G. Foti and E. Rimini. J. Appl. Phys. 50 (1979) 788.