Photon Factory Activity Report 2018 #36 (2019)

BL-11D/2017G041

Local valence electronic states of HfSi2 islands on Si(110)-16 × 2 substrate
Takuhiro KAKIUCHI1,*, Daisuke KOYAMA1, and Kazuhiko MASE2, 3
1Ehime University, 2-5 Bunkyo-cho, Matsuyama, Ehime 790-8577, Japan2
Photon Factory, KEK, 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan
3
SOKENDAI, 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan

Si 2p1/2, 3/2 photoelectron count (kcps)

2 Experiment
A clean Si(110)-16×2 with single domain (SD) surface
was prepared by direct current heating over 1523 K in
ultrahigh vacuum (UHV) less than 2.0 × 10-7 Pa [2]. Afterthen, ultrathin Hf films with the different thicknesses of~0.5, 1.0, 2.0, 6.0, and 8.0 ML (monolayer, 1 ML = 2.4 Å[3]) were deposited on a clean Si(110)-16×2 surface. Thesesamples were directly turned into i-HfSi2/Si(110) structureby annealing at 1073 K.
After annealing at 1073 K

15i-HfSi2(1.0 ML)/Si(110)hν = 130 eV

Measurment dataFitting line
Bulk (0.00 eV)
HfSi2 (-0.42 eV)
Si surface(+0.29 eV)
Si+ (+0.95 eV)105043210-1-2

Relative binding energy (eV)Fig. 1: Si 2p1/2, 3/2 photoelectron spectrum of iHfSi2/Si(110) substrate.

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 2p1/2, 3/2 core levels.
3 Results and Discussion
In Fig. 1, Si 2p1/2, 3/2 photoelectron spectra of iHfSi2/Si(110) show a Hf disilicide component (HfSi2) at 0.42 eV on the relative binding energy axis. All iHfSi2/Si(110) samples show the existence of HfSi2component. The intensity of HfSi2 increases as the Hf
thickness before annealing increases from 0.5 to 8.0 ML.
Fig. 2 shows the Si-L23VV-Si-2p APECS spectra which
selected the only HfSi2 component from all i-HfSi2/Si(110)samples. These are drawn on two-holes binding energy
scale of Si L23VV Auger final states. When comparing theseresults, they are mostly the same spectral distributions.
This indicates that the local valence electronic state at
HfSi2 surface component does not depend on thickness ofHf deposition films before annealing because the HfSi2islands with random sizes are formed on Si(100)-16×2surface.
Acknowledgement
This work was supported by a Grant-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] K. Sakamoto et al., Phys. Rev. B 79, 045304 (2009).
[3] X. Zhao et al., Phys. Rev. B 65, 233106 (2002).
* kakiuchi.takuhiro.mc@ehime-u.ac.jp
APECS Intensity (arb.unit)

1 Introduction
Drastic downsizing of metal-oxide-semiconductor field
effect transistor (MOS-FET) caused a critical leakage
current through ultrathin silicon dioxide (SiO2) gate film(< 20 Å) due to direct tunneling effect. Therefore, ahafnium dioxide (HfO2, k = ~25) as high dielectric constantmaterial is attracting high attentions as an alternative for
SiO2. The application of HfO2 into MOS-FET will offerthat the physical thickness of the gate oxide film could be
increased for reduction of serious leakage current.
Nevertheless, a matter is that hafnium silicide (HfSi2)
component which generates around interface of HfO2/Si
structure will cause unstable behaviors of the MOS-FET
because they have narrower bandgap in comparison withHfO2. So, it is important to reveal the local valence electricstate of HfSi2 depending on the size, thickness, chemical
environment, and so on. [1]In this study, 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-HfSi2component with Si L23VV Auger-electron – Si 2p
photoelectron coincidence spectroscopy (Si-L23VV-Si-2p
APECS). The core-valence-valence (CVV) Auger electron
spectrum measured with Si-L23VV-Si-2p APECS canprovide the two holes valence electronic structure in thevicinity of a specific i-HfSi2 component.

1.4
HfSi2: Surface Component
1.2
Si-L23VV-Si-2p APECS
1.0
0.8
0.6
0.4
0.2 ▼ HfSi2(0.5 ML)/Si(110) APECS
0.0 ◆ HfSi2(1 ML)/Si(110) APECS-0.2 ■ HfSi2(2 ML)/Si(110) APECS● HfSi2(6 ML)/Si(110) APECS-0.4 ▲ HfSi (8 ML)/Si(110) APECS2-0.61210864h = 130 eV

20-2

Two Holes Binding Energy (eV)Fig. 2: Si-L23VV-Si-2p APECS obtained from iHfSi2/Si(110) with the thicknesses from 0.5 to 8 ML.