Investigation of ZrGe Schottky source/drain contacts
for Ge p-channel MOSFETs
H. Yang
a,b,
n
, J. Gao
a
, H. Nakashima
b
a
Key Laboratory of Optical System Advanced Manufacturing Technology, Changchun Institute of Optics, Fine Mechanics and Physics,
Chinese Academy of Sciences, No. 3888 Dongnanhu Road, Changchun 130033, China
b
Art, Science and Technology Center for Cooperative Research, Kyushu University, 6-1 Kasuga-koen, Kasuga, Fukuoka 816-8580, Japan
article info
Keywords:
Schottky source/drain
Zirconium germanide
Metal Ge contact
Ge MOSFET
Hole mobility
abstract
Zirconium germanide (ZrGe) Schottky source/drain (S/D) contacts were fabricated on n-Ge
substrates using direct sputter deposition of Zr. The electrical properties of ZrGe/n-Ge
contact were investigated and an excellent Schottky characteristic with an electron barrier
height of 0.59 eV was obtained, implying an extremely low hole barrier height of 0.07 eV.
Using ZrGe as S/D, the operation of Schottky Ge p-channel metal-oxide-semiconductor
field-effect transistor (MOSFET) was well demonstrated without any S/D impurity doping.
Its good performance indicates that ZrGe is available to S/D in Schottky Ge p-MOSFET.
& 2014 Elsevier Ltd. All rights reserved.
1. Introduction
Mobility enhancement has been regarded as one of the
most powerful technology boosters to overcome scaling
limits of traditional silicon (Si) metal-oxide-semiconductor
field-effect transistor (MOSFET) [1]. Among high mobility
materials, Ge is of great interest as a substitute for Si for
future high-performance MOSFETs due to its higher intrin-
sic carrier mobility and relative compatibility with Si
processing. To realize high-performance Ge MOSFETs, both
source/drain (S/D) engineering and gate-stack engineering
are crucial. With the significant progress in gate-stack
engineering [2–5], Ge-based MOSFETs with good perfor-
mance have been demonstrated. However, ultra-shallow
highly-doped S/D junction formation remains a techn-
ology bottleneck to develop high-performance aggres-
sively scaled Ge MOSFETs because of large diffusion
coefficients and low solubility limits of dopant impurities
in Ge [6–9]. In addition, a low-temperature processing is
essential for Ge MOSFET fabrication. Therefore, conven-
tional doped S/D technology is difficult to satisfy the
requirement of future Ge MOSFETs. As a substitute for
doped S/D, metal Schottky S/D is considered as a potential
approach to form ultra-shallow S/D junction on Ge sub-
strates because it has low-temperature processing and
does not need the complex procedure of implant and
activation annealing [1].
To realize ideal metal Schottky S/D, barrier height is a
crucial parameter. It should be as low as possible to enhance
drive current and suppres s leakage curr ent. Theoretical
studies have shown that the hole barrier height (Φ
BP
)
of Schottky S/D should be less than 0.1 eV for Schottky
p-MOSFETs in order to outperform doped S/D devices [10].
Thanks to the Fermi-level pinning (FLP) near the valence
band edge of Ge at the metal/Ge interface [1 2],metal/Ge
contact with low Φ
BP
is formed more easily than that with
low electron barrier height (Φ
BN
), and therefore metal
Schottky S/D is more promising for practical application in
Ge p-MOSFETs instead of n-MOSFETs. Among various metal
germanide, nickel germanide (NiGe)/Ge and platinum
Contents lists available at ScienceDirect
journal homepage: www.elsevier.com/locate/mssp
Materials Science in Semiconductor Processing
http://dx.doi.org/10.1016/j.mssp.2014.05.025
1369-8001/& 2014 Elsevier Ltd. All rights reserved.
n
Corresponding author at: Key Laboratory of Optical System Advanced
Manufacturing Technology, Changchun Institute of Optics, Fine
Mechanics and Physics, Chinese Academy of Sciences, No. 3888
Dongnanhu Road, Changchun 130033, China. Tel.: þ86 431 86708126.
E-mail address: yanghg@ciomp.ac.cn (H. Yang).
Materials Science in Semiconductor Processing 26 (2014) 614–619