Stress Effect on the Reaction Kinetics of Metal/Silicon
systems
計畫編號：甲-91-E-FA04-1-4
執行期限：94 年 4 月 1 日至 95 年 3 月 31 日
主持人：C.J. Tsai
計畫參與人員：W.C. Lin, Y.C. Chu, and L.H. Wu
Department of Materials Science and Engineering, National Tsing Hua University,
Hsinchu, Taiwan, ROC
Ⅰ. Abstract
device7. In our previous experiments, the
external stress we exert using a mechanical
From
the
results
of
previous
experiments, the stress effect on silicidation
process only can be observed in the Ni/Ti/Si
system. In the TiN/Ti/Si system, although the
transformation temperature of silicide does
not change with a tensile stress induced by
the TiN layer existing on the Ti/Si interface,
the Ti-Si intermixing layer is thicker in the
sample with a larger tensile stress. These
results indicate that the external stress we
method having a maximum magnitude about
300MPa seems to have no influence on the
silicidation process in the Ni/Si and Ti/Si
system. In the Ni/Ti/Si system, a result of
tensile (compressive) strss retards (enhances)
the silicidation process is observed. It implies
that the thin Ti interlayer in the Ni/Ti/Si
system is a key point to let the external stress
have the ability to influence the phase
transformation temperature. In the TiN/Ti/Si
exert in these experiments could influence
the mobility of atoms during the annealing
process but does not have enough energy to
change
the
temperature
of
phase
transformation. It is the reason that the
activation energy of the phase transformation
is usually larger than the activation energy of
the mobility. Besides, the stress field
distribution of the periodic nano-scale-pattern
NiSi2 templates which we fabricate using
system, a tensile stress forms on the Ti/Si
interface due to the large compressive stress
in the TiN layer. The results of the TiN/Ti/Si
system show that the tensile stress obviously
enhances the mobility of Si but does not
change
the
temperature
of
phase
transformation during the annealing process.
So we conjecture that the external stress we
exert is only enough to influence the mobility
of atoms because the activation energy of the
polystyrene nanosphere lithography
simulated using a finite element method.
mobility is usually smaller than the activation
energy of the phase transformation. Therefore,
the tensile stress retards the silicidation
process observed in the Ni/Ti/Si system
might be due to the tensile stress let more Si
mix with Ti interlayer at low temperature,
and the formation of Ni silicide become more
difficult because more Ti atoms must be
segregate from the Si during the phase
is
Ⅱ. Introduction
Stress is found to influence the rate of
chemical reaction1,2, the formation and
stability of phase3,4, the nucleation site of
epitaxial growth5,6, and even the property of
1
transformation process.
Using the finite element method to
simulate the stress field of Ge islands on Si
substrate has shown a good agreement with
the measurement results8-10, and it indicate
that this method is reliable to calculate the
stress filed in a nano-scale structure
especially when the structure with a epitaxial
relation with the substrate. The lattice
mismatch between the NiSi2 and the Si
substrate is -0.46％ at room temperature and
100
90
F/W (N/m)
80
70
60
50
40
30
20
5
10
15
20
25
Thickness of TiN (nm)
Fig. 1. The F/W for TiN/Ti/Si system with TiN layer
this mismatch is smaller than the different
between the Ge and Si. For this reason, the
elastic condition used to simulate the stress
field in the Ge islands should be proper to
from 5nm to 25nm. At thickness above 20 nm, the
use in the periodic nano-scale-pattern NiSi2
templates which we fabricate previously. The
stress field of the standard epitaxial structure
of NiSi2/Si(100) is simulated using a finite
element analysis software, FEMLAB 3.1, in
this experiment.
increasing convex with increasing thickness
of the TiN layers, which causes an tensile
stress on the Ti/Si interface. The TEM
images for the samples with 5 and 25nm TiN
layer after annealing at 300℃ are shown in
F/W saturated.
It can be seen clearly that the sample is
Fig. 2 (a), and (b). Ti-Si intermixing layers
are found to grow thicker between the Ti
layer and the Si substrate in both samples and
the thickness of intermixing layer is 2.2nm in
Fig. 2 (a) and 3.5nm in Fig. 2 (b). The
intermixing layer would grow as the
annealing temperatures increase but at the
same annealing temperature the intermixing
layers are always thicker in samples with
thicker TiN thickness. The diffusion behavior
Ⅲ. Results and Discussion
The TiN/Ti/Si structure was deposited
using a sputter system at a base pressure of 1
×10-8 torr. The TiN layer usually has a large
compressive stress11 and it will exert a tensile
stress on the interface of Ti and Si. The
magnitude of the tensile stress on the
TiN(5nm)/Ti/Si
interface of Ti and Si can be controlled by
modify the thickness of the TiN layer. In this
experiment, the range of the TiN thickness is
from 5nm to 25nm and the thickness of Ti
layer is 25nm for all samples. The initial F/W
which is proportional to curvature for the
TiN/Ti/Si as a function of TiN layer
thickness
is
shown
in
Fig.
1..
TiN(25nm)/Ti/Si
TiN
TiN
Ti
Ti
Ti+Si mixing layer
Ti+Si mixing layer
Si
Si
(a)
(b)
Fig. 2. TEM images of samples after annealed at 300
℃. The thickness of TiN layer is 5nm in (a) and 25nm
in (b).
2
Peak Height of Si (a.u.)
1.0x10
6
8.0x10
5
6.0x10
5
4.0x10
5
2.0x10
5
and
the
stress
TiN 5nm
TiN 25nm
0.0
z
0
100
200
300
400
500
600
Sputtering Time (sec)
y
(a)
x
Fig. 3. The AES depth profile of Si atoms for
y
TiN(5nm)/Ti/Si and TiN(5nm)/Ti/Si system after
x
annealed at 300℃.
of Si atoms for the samples shown in Fig. 2 is
detected by AES (Fig. 3). From the result of
distribution of Si shown in Fig. 3, it can
confirm that the mobility of Si is enhanced at
a in-plane tensile stress state. The phase
transformation temperatures of Ti silicide do
not change for samples with different TiN
thickness from the results of XRD (not show
(b)
(c)
(d)
(e)
here). Compare with the results in the Ni/Si
and Ti/Si system, the phase transformation
temperature of silicide might be difficult to
change under a stress below 300MPa.
The stress field of the Si capped layer
upon the standard epitaxial structure,
trough-shape protuberance of NiSi2 into Si
boundary by {111} planes12,13, of
NiSi2/Si(100) is simulated using the finite
element method. Fig. 4 (a) shows the
Fig. 4. (a) The structure used to simulate the stress
structure used to simulate the stress field. Fig.
4 (b) is the x direction normal stress field on
the surface of the Si capped layer and Fig. 4
(c) is the x direction normal stress variation
along the x direction. The stress is tensile
outside the area projected by the NiSi2 dot,
and gradually change to compressive as the
center of NiSi2 dots approached. Fig. 4 (d)
and (e) is the x direction normal stress field
NiSi2 dot. The controllable nano-scale stress
field shown in Fig. 4 (b) is potential for
future application.
field. (b) The x direction normal stress field and (c)
the x direction normal stress variation along the x
direction, on the surface of the Si capped layer. (d)
The x direction normal stress field and (e) the x
direction normal stress variation along the x direction,
on the plane of NiSi2 surface..
variation on the plane of the NiSi2 surface.
The stress is highly tensile in the interior of
Ⅳ. Self-evaluation
From the result of stress effect in the
Ti/Si, Ni/Si, Ni/Ti/Si, and TiN/Ti/Si system,
3
the stress we exert using a mechanical
[11] A. J.Perry, J. N. Matossian, S. J. Bull, D.
method only can influence the mobility of
atom. But if a thin interlayer exists in a
system, it might have the ability to influence
the formation temperature of silicide
indirectly. The stress distribution of the
periodic nano-scale-pattern NiSi2 templates
has been simulated using a finite element
method. It can help us to predict the stress
state in a nano-scale structure which is
difficult to measurement in experiment.
I. Proskurovsky, and etc. Metallurgical
and Materials Transactions A. 30 2931
(1999).
[12] J. P. Sillivan, R. T. Tung, and F. Schery,
J. Appl. Phys., Vol. 72, 478, (1992).
[13] R. T. Tung, J. M. Gibson, J. M. Poate,
Phys. Rev. Lett., Vol. 50, 429, (1983).
Ⅴ. Reference
[1] J. Tersoff, Yuhai Tu, and G. Grinstein,
Appl. Phys. Lett, 73, 2328 (1998).
[2] K. S. Kim, J. A. Hurtado, and H. Tan,
Phys. Rev. Lett, 83, 3872 (1999).
[3] E. M. Schaller, B. I. Boyanov, S. English,
and R. J. Nemanich, J. Appl. Phys. 85,
3614 (1999).
[4] S. L. Cheng, H. M. Lo, L. W. Cheng, and
L.J. Chen, Thin Solid Films, 424, 33
(2003).
[5] S. Y. Shiryaev, F. Jensen, J. L. Hansen,1
J. W. Petersen, and A. N. Larsen, Phys.
Rev. Lett, 78, 503 (1997).
[6] G. Jin, J. L. Liu, S. G. Thomas, Y. H. Luo,
and K. L. Wang. Appl. Phys. Lett. 75,
2752 (1999).
[7] A. K. Fung, L. Cong, J. D. Albrecht, M. I.
Nathan, P. P. Ruden, and H. Shtrikman, J.
Appl. Phys. 81, 502 (1997).
[8] S. Christiansen, M. Albrecht, H. P.
Strunk, and H. J. Maier, Appl. Phys. Lett.
64, 3617 (1994).
[9] A. E. Romanov, G. E. Beltz, W. T.
Fischer, P. M. Petroff, and J. S. Speck, J.
Appl. Phys. 89, 4523 (2001).
[10] Q. X. Pei, C. Lu, and Y. Y. Wang, J.
Appl. Phys. 93, 1487 (2003).
4