1063-7397/03/3205- $25.00 © 2003 MAIK “Nauka /Interperiodica”
0275
Russian Microelectronics, Vol. 32, No. 5, 2003, pp. 275–281. Translated from Mikroelektronika, Vol. 32, No. 5, 2003, pp. 344–351.
Original Russian Text Copyright © 2003 by A. G. Vasiliev, A. L. Vasiliev, Zakharov, Orlikovsky, Horin, Eindou.
INTRODUCTION
In metallization systems, contact layers serve to
decrease source and drain contact resistances and the
surface resistances of terminating regions; they also
reduce resistance–capacitance delays. Materials to be
used in contact layers should have low resistivity and
ensure low contact resistance with respect to adjacent
p- and n-regions; they should also be resistant to tem-
perature changes, electromigration, etc. Metal silicides
meet these requirements to a large extent.
The self-aligned silicide (SALICIDE) process is
very useful in the fabrication of high-speed comple-
mentary metal–oxide–semiconductor (CMOS) circuits.
At present this technology widely employs TiSi
2
and
CoSi
2
films [1]. An advantage of TiSi
2
is its low resis-
tivity (
Ϸ
15
µ
Ω
cm) in the thermodynamically stable
phase C54. Its main disadvantage is the formation of
the high-resistivity metastable phase C49 in contact
windows under annealing; this increases the contact
resistance with respect to the n
+
-Si and p
+
-Si regions. It
has been reported that the nucleation of the C54 phase
occurs on C49 grain boundaries [2]. These conditions
greatly inhibit the C49-to-C54 phase transformation,
due to the low density of nucleation sites. In practical
terms the drawback puts a lower limit of about 250 nm
on feature sizes.
In sub-200-nm technologies, TiSi
2
gave way to
CoSi
2
, whose properties are far less affected by device
geometry [3]. Compared with TiSi
2
, better selectivity
can be achieved in the etching of a metal on SiO
2
with
respect to CoSi
2
on Si. Thin films of CoSi
2
show lower
stresses and higher chemical stability; in particular,
they do not react with impurities to produce high-resis-
tivity compounds. Also note that, in the annealing of a
metal–silicon system, the migrating species are atoms
of Co, not Si; as a result, the spacers are free from sili-
cide layers, which tend to cause short-circuiting.
For sub-100-nm technologies, NiSi is being evalu-
ated as a candidate material of contact layers [4]. Com-
pared with TiSi
2
and CoSi
2
, the production of NiSi
requires smaller amounts of Si. Moreover, NiSi films
have a low resistivity (
Ϸ
10
µ
Ω
cm), a reasonable tem-
perature of formation (350–750
°
C), a low stress (6
×
10
–9
dyn/cm), and small contact resistances. Devices
based on NiSi do not suffer from gate–source or gate–
drain short-circuiting. The surface resistivity of NiSi is
independent of line width for the stated feature sizes.
Some workers addressed volume solid-state reactions
between a binary alloy and a silicon substrate [5–8]. It has
been shown that the silicide formation is governed by
the interaction of the metals and the silicon with each
other [8]. Primary importance is attached to the case
where the alloy contains a refractory metal M
1
and a
near-noble metal M
2
. The minimum temperature at
which the reaction takes place is the temperature of for-
mation for M
2
Si
x
. It is the near-noble metal that plays
the major part in the silicide formation. Annealing at a
moderate temperature causes the diffusion of M
2
into
the substrate, with the result that an M
1
layer and a sili-
cide layer are formed on the surface. At higher anneal-
ing temperatures, Si diffuses from the substrate into the
M
1
layer, so that an
M
1
Si
x
/M
2
Si
y
/Si
structure is pro-
duced.
Phase Formation in a Ta–Ni–N Thin Film during
Its Electron-Beam Evaporation Deposition
on a Heated Si(100) Substrate
A. G. Vasiliev
1,2
, A. L. Vasiliev
3,4
, R. A. Zakharov
5
, A. A. Orlikovsky
1
,
I. A. Horin
1
, and M. Eindou
4
1
Institute of Physics and Technology, Russian Academy of Sciences, Moscow, Russia
2
Moscow State Institute of Radio Engineering, Electronics, and Automation (Technical University), Moscow, Russia
3
Shubnikov Institute of Crystallography, Russian Academy of Sciences, Moscow, Russia
4
Institute of Materials Science, University of Connecticut, USA
5
Institute of Nuclear Physics, Moscow State University, Moscow, Russia
Received March 4, 2003
Abstract
—Surface-diffusion reactions between a Ta–Ni–N alloy and a Si(100) substrate are studied experi-
mentally. It is shown that a
Ta
x
Si
y
N/NiSi
2
bilayer can be produced on the substrate by simultaneous electron-
beam evaporation of tantalum and nickel in a nitrogen atmosphere, the substrate being heated to about 800
°
C.
The formation of the NiSi
2
phase is examined.
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