通过HCl和（NH4）2S表面钝化的高迁移率锗p-MOSFET
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CPB Online In-PressCPB Online In-Press
Chin. Phys. B Vol. 22, No. 10 (2013) 107302
High-mobility germanium p-MOSFETs by using
HCl and (NH
4
)
2
S surface passivation
∗
Xue Bai-Qing(薛百清), Wang Sheng-Kai(王盛凯)
†
, Han Le(韩 乐), Chang Hu-Dong(常虎东),
Sun Bing(孙 兵), Zhao Wei(赵 威), and Liu Hong-Gang(刘洪刚)
‡
Microwave Device and IC Department, Institute of Microelectronics, Chinese Academy of Sciences, Beijing 100029, China
(Received 26 March 2013; revised manuscript received 6 May 2013)
To achieve a high-quality high-κ /Ge interface for high hole mobility Ge p-MOSFET applications, a simple chemical
cleaning and surface passivation scheme is introduced, and Ge p-MOSFETs with effective channel hole mobility up to
665 cm
2
/V·s are demonstrated on a Ge (111) substrate. Moreover, a physical model is proposed to explain the dipole layer
formation at the MOS interface by analyzing the electrical characteristics of HCl- and (NH
4
)
2
S-passivated samples.
Keywords: Ge, MOSFET, high-k dielectric, mobility
PACS: 73.40.Qv, 71.55.Eq, 77.55.D– DOI: 10.1088/1674-1056/22/10/107302
1. Introduction
Germanium is a promising candidate for advanced metal–
oxide–semiconductor field effect transistors (MOSFETs) be-
cause of its superior carrier mobility compared with silicon.
However, the presence of undesirable native oxide is one of
the major obstacles to the heterogeneous integration of Ge
MOSFETs with Si integrated circuits.
[1]
Completely remov-
ing the defective native oxide from the Ge surface is essential
to realizing high-performance Ge MOSFETs. Many attempts
have been made to apply Si-cleaning processes for the treat-
ment of Ge surfaces, but the results have been poor. Sun et
al.
[2]
showed that the use of conventional hydrogen fluorine
(HF) solutions does not effectively remove the GeO
x
from the
Ge surface, but instead, made its surface rougher. Using hy-
drogen chloride (HCl) and hydrogen bromine (HBr)
[2,3]
were
investigated to remove the GeO
x
, however the cleaned Ge sur-
faces were easily reoxidized in the air. Therefore, a subse-
quent surface passivation step may improve the interface per-
formance of high-κ dielectric and Ge. Several Ge passivation
techniques including surface or interfacial nitridation,
[4]
S-
passivation,
[5–7]
Si-passivation,
[8]
and F-passivation,
[9]
have
been applied to improve the stability of high-κ/Ge systems.
However, these passivation methods are carried out in the HF-
last process. Chemical passivation followed by HCl cleaning
has rarely been reported. Moreover, from the aspect of sub-
strate orientation engineering, which is known to be effective
for the mobility enhancement of Ge MOSFETs, Ge (110) p-
MOSFETs have been confirmed as having the highest hole
mobility
[10]
of all orientations, such as Ge (100) and Ge (111).
However, the impacts of surface chemical passivation on Ge
substrate with orientations have not been systematically inves-
tigated so far.
In this paper, we introduce a simple chemical cleaning
and surface passivation scheme using HCl and (NH
4
)
2
S to
achieve a high-quality high-κ /Ge interface for high mobility
Ge p-MOSFETs application. Effective channel hole-mobility
up to 665 cm
2
/V·s has been achieved on a Ge (111) substrate.
To reveal the effects of chemical passivation, C–V and I–V
characterizations were performed, and the mobility scattering
mechanism on Ge (100), (110), and (111) substrates is dis-
cussed. Moreover, a physical model is proposed to explain the
dipole layer formation at the MOS interface by analyzing the
electrical characteristics of HCl and (NH
4
)
2
S passivated sam-
ples.
2. Device fabrication
The n-type Ge wafers used in this work have a resistivity
of approximately 0.01 Ω·cm–0.1 Ω·cm. These Ge wafers were
pre-cleaned in acetone and alcohol for 5 min, respectively,
and rinsed in deionized water (DIW) to dissolve any surface
solvent. To remove the surface native oxide (GeO
x
), the Ge
wafers were immersed in a diluted HCl (30% v/v) solution for
60 s, then rinsed in DIW. After the cleaning process, some
wafers were soaked in HCl (30% v/v) solution for 10 min,
while others were treated in (NH
4
)
2
S solution for 10 minutes,
followed by DIW rinsing and N
2
drying. The treated samples
were immediately transferred into the load-lock chamber of
an atomic layer deposition (ALD) system (Beneq TFS200).
Then, 10-nm-thick Al
2
O
3
films were deposited on the as-
passivated substrates at 300
◦
C, using trimethylaluminium
∗
Project supported by the National Basic Research Program of China (Grant Nos. 2011CBA00605 and 2010CB327501), the National Natural Science Foun-
dation of China (Grant No. 61106095), and the National Science and Technology Major Project of the Ministry of Science and Technology of China (Grant
No. 2011ZX02708-003).
†
Corresponding author. E-mail: wangshengkai@ime.ac.cn
‡
Corresponding author. E-mail: liuhonggang@ime.ac.cn
© 2013 Chinese Physical Society and IOP Publishing Ltd http://iopscience.iop.org/cpb http://cpb.iphy.ac.cn
107302-1
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