Effects of carbon pre-silicidation implant into Si substrate on NiSi
Jun Luo
a,b,
⇑
, Zhi-Jun Qiu
c
, Jian Deng
a
, Chao Zhao
a
, Junfeng Li
a
, Wenwu Wang
a
, Dapeng Chen
a
,
Dongping Wu
c
, Mikael Östling
b
, Tianchun Ye
a
, Shi-Li Zhang
b,c,d
a
Key Laboratory of Microelectronics Devices & Integrated Technology, Institute of Microelectronics, Chinese Academy of Sciences, Beijing 100029, PR China
b
Royal Institute of Technology (KTH), Electrum 229, Stockholm 164 40, Sweden
c
State Key Laboratory of ASIC and System, Fudan University, Shanghai 200433, PR China
d
Uppsala University, Solid-State Electronics, The Ångström Laboratory, Uppsala 751 21, Sweden
article info
Article history:
Available online 23 August 2013
Keywords:
Carbon implant
Thermal stability
NiSi
abstract
In this work, the effects of carbon pre-silicidation implant into Si(1 00) substrate on NiSi were investi-
gated. NiSi films with carbon pre-silicidation implant to different doses were characterized by means
of sheet resistance measurements, X-ray diffraction, scanning electron microscopy (SEM), planar view
transmission electron microscopy (TEM) and second ion mass spectroscopy (SIMS). The presence of C
is found to indeed significantly improve the thermal stability of NiSi as well as tends to change the pre-
ferred orientations of polycrystalline NiSi. The homogeneously distributed C at NiSi grain boundaries and
C peak at NiSi/Si interface is ascribed to the improved thermal stability of NiSi. More importantly, the
dose of carbon pre-silicidation implant also plays a key role in the formation of NiSi, which is suggested
not to exceed a critical value about 5 10
15
cm
2
in practical application in accordance with the results
achieved in this work.
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
Nickel monosilicide, i.e., NiSi, as well as its derivatives such as
Ni(Pt)Si, has been used as the wide-spread material of choice for
contact metallization in aggressively down-scaled complementary
metal–oxide-semiconductor (CMOS) devices [1–2]. NiSi films offer
low specific resistivity, low contact resistivity, low formation tem-
perature, and low consumption of Si during silicide formation [3,4].
However, thin films of NiSi often suffer from poor morphological
stability and start to agglomerate at 500 °C as a result of low melt-
ing point of NiSi at 992 °C indicating very high atomic diffusivity of
both Ni and Si [1,3]. In order to stabilize NiSi films, the addition of a
third element like Pt, Ti, N and C were usually adopted [5–9].
Among them, C incorporation has been shown to be effective in
suppressing the agglomeration of NiSi thus improving its morpho-
logical stability [8–12]. In addition, incorporating C substitution-
ally in the source/drain regions has also been demonstrated to
generate a tensile strain in the channel of n-type MOS field-ef-
fect-transistors (MOSFETs) [13]. Furthermore, it is shown recently
that cold C implant or co-implanting C into the source/drain re-
gions can effectively suppress rapid boron and phosphorus diffu-
sion in Si, thus achieving ultra-shallow junctions in the 22-nm
CMOS technology nodes and beyond [14–16]. We have previously
reported that the incorporation of C indeed leads to the improved
thermal stability of NiSi [17] but how the carbon pre-silicidation
implant exerts influence on NiSi is not very clear. In this paper,
we therefore systematically investigate the effects of carbon pre-
silicidation implant with a series of doses into Si substrate on NiSi.
2. Experimental
P-type Si(100) wafers with a resistivity of 20–40
X
-cm were
used as the starting material. Using a thermally grown 3-nm-thick
SiO
2
as screen oxide, carbon ions with a series of doses varying
from 0 to 2 10
16
cm
2
were implanted into the Si substrate at en-
ergy of 3 keV. According to SRIM simulation [18], C should peak at
10 nm below the Si wafer surface. After stripping the screen SiO
2
,
a 10-nm-thick nickel film was sputter-deposited. The wafers were
then sliced to small sample pieces about 2 cm 2 cm in size. Sub-
sequently, the samples were annealed isochronally for 30 s in a ra-
pid thermal processing (RTP) chamber in N
2
from 425 to 800 °C.
Any unreacted Ni was stripped off using an H
2
SO
4
:H
2
O
2
(4:1) solu-
tion at 120 °C. The as-prepared NiSi samples were characterized
using four-point probe measurement for sheet resistance (R
sh
),
the usual h-2h diffractometer equipped with a Cu tube and a
post-sample monochromator for phase formation, scanning elec-
tron microscopy (SEM) for both surface and interface morphology,
planar view transmission electron microscopy (TEM) for the obser-
vation of grains, and second ion mass spectroscopy (SIMS) for the
distribution of carbon after Ni silicidation.
0167-9317/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.mee.2013.08.010
⇑
Corresponding author at: Key Laboratory of Microelectronics Devices &
Integrated Technology, Institute of Microelectronics, Chinese Academy of Sciences,
Beijing 100029, PR China. Tel./fax: +86 10 82995684.
E-mail address: luojun@ime.ac.cn (J. Luo).
Microelectronic Engineering 120 (2014) 178–181
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Microelectronic Engineering
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