Photon Factory Activity Report 2017 #35 (2018)

BL-11D/2017G041

Local Valence Electronic State of HfSi2 Surface Component on Low-IndexedSi(110) Substrate
Takuhiro TAKIUCHI1,*, Daisuke KOYAMA1, Kazuhiko MASE2, 3, and Shin-ichi NAGAOKA1
1Ehime University, 2-5 Bunkyo-cho, Matsuyama, Ehime 790-8577, Japan2
Photon Factory, 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan
3
SOKENDAI, 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan

2 Experiment
A clean Si(110)-16×2 with SD surface was prepared bydirect current heating over 1523 K in UHV less than 2.0 ×
10-7 Pa. After then, ultrathin Hf films with the different
thickness of ~2, 6, and 8 ML (monolayer, 1 ML = 2.4 Å[4]) were deposited on the clean Si(110)-16×2 surface bymeans of electron bombardment method. They weredirectly turned into i-HfSi2/Si(110) structure by annealing
at 1073 K.

Si-L23VV-Si-2p APECS measurements were performed
with a handmade electron-electron-ion coincidence
analyzer at BL-11D in PF, KEK. The photon energy (h)was fixed at 130 eV for ionization of Si 2p core levels.
3 Results and Discussion
Fig. 1 shows the Si-L23VV-Si-2p APECS spectra which
selected the only HfSi2 surface component from some iHfSi2/Si(110) structures. These are drawn on two-holes
binding energy scale of Si L23VV Auger final states. When
comparing these results, they are mostly the same spectral
distributions. This indicates that the local valence
electronic state at HfSi2 surface component does notdepend on the thickness of Hf deposition films because
the HfSi2 islands with random sizes are formed after
annealing at 1073 K.

APECS Intensity (arb.unit)

1 Introduction
Downsizing of metal-oxide-semiconductor field effecttransistor (MOS-FET) in development of silicon
semiconductor industry has achieved large integration,high speed processing, light weighting, and on. On theother hand, it has led to a critical issue that a leakage
current through ultrathin silicon dioxide (SiO2) film (< 20Å) as gate insulating film happens due to direct tunneling
effect. Therefore, a hafnium dioxide (HfO2, k = ~25) ashigh dielectric constant material is attracting highattentions as an alternative for SiO2 in order to prevent theleakage current. The application of HfO2 into MOS-FET
will offer that the physical thickness of the gate oxide
film could be increased for reduction of serious leakage
current. Nevertheless, a matter that arises here is thathafnium silicide (HfSi2) component which inevitably
generates around interface of HfO2/Si structure will cause
unstable behaviors of the MOS-FET because they havenarrower bandgap in comparison with HfO2. Therefore, it
is important to reveal the local valence electric states ofHfSi2/Si structure depending on the size, thickness,chemical environment, and so on. [1]In addition, the MOS-FET structure renewed from 2
dimensions (Ds) to 3Ds will be another approach so as tokeep up with the development of MOS-FET performance.
Therefore, low-indexed Si(110) substrate which shows
unique single domain (SD) structure with atomic scaled
3Ds concave-convex is also an promising candidate fornext generation.[2, 3]
In this report, we prepared HfSi2 islands on a clean
Si(110)-16×2 surface [i-HfSi2/Si(110)] and investigatedsite specific local valence electronic state of i-HfSi2surface component with Si L23VV Auger-electron – Si 2p
photoelectron coincidence spectroscopy (Si-L23VV-Si-2pAPECS). The core-valence-valence (CVV) Auger electronspectrum measured with Si-L23VV-Si-2p APECS canprovide the two holes valence electronic structure in thevicinity of a specific i-HfSi2 component.

1.2 HfSi2 surface component
Si-L23VV-Si-2p APECS
1.0h = 130 eV

0.8
0.60.4■ HfSi2(2 ML)/Si(110) APECS

0.2 ● HfSi2(6 ML)/Si(110) APECS0.0▲ HfSi2(8 ML)/Si(110) APECS

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Two-Holes Binding Energy (eV)Fig. 1: Si-L23VV-Si-2p APECS spectra obtained from iHfSi2/Si(110) which made from ultrathin Hf deposition
films with the different thicknesses of ~2, 6, and 8 ML byannealing at 1073 K.
Acknowledgement
This work was supported by Grants-in-Aid for
Scientific Research (No. 17K06030) from the Japanese
Ministry of Education, Culture, Sports, Science andTechnology. We thank the PF staff for creating thistemplate.
References[1] A. I. Kingon et al., Nature 406, 1032 (2000).
[2] Y. Yamada et al, Phys. Rev. B 77, 153305 (2008).
[3] K. Sakamoto et al., Phys. Rev. B 79, 045304 (2009).
[4] X. Zhao et al., Phys. Rev. B 65, 233106 (2002).
* kakiuchi.takuhiro.mc@ehime-u.ac.jp