Photon Factory Activity Report 2005 #23Part B (2006)
Surface and Interface

2C/2002S2-002

Mechanism of the interfacial reaction for polycrystalline-Si /HfO2/Si gate stacks
with UHV annealing studied by photoemission spectroscopy
Haruhiko TAKAHASHI1*, Satoshi TOYODA1, Jun OKABAYASHI1, Hiroshi KUMIGASHIRA1,Masaharu OSHIMA1, Kazuto IKEDA2, Guo-Lin LIU2, Ziyuan LIU2, and Koji USUDA2
1
The University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan
2
STARC, Kohoku-ku, Kanagawa 222-0033, Japan
Introduction
In previous reports, we investigated the mechanism ofsilicidation on annealing temperature in ultrahigh vacuum(UHV) [1]. We have found that Hf silicide (HfSi2) isformed at the “upper interface” between poly-Si
electrodes and HfO2 gate dielectrics at 700 °C for 10 min.
At 750 °C annealing, silicidation propagates rapidly fromthe upper interface to the “lower interface” between HfO2gate dielectrics and Si substrates. The annealing-timedependence of photoemission spectra can provide us with
important information to understand the mechanism forsilicidation.

46

Users' Reportθ = 60 º× 20104102100Intensity (arb. units)

poly-Si
X106(b)

Si 2p hν = 800 eV

θ=0º98poly-Si× 20X106104

Binding Energy (eV)10210098

Binding Energy (eV)Fig. 1. Si 2p photoemission spectra by the 700 °C
annealing for 1 min at the emission angles of (a) 0 °and (b) 60 °.
Hf 4f hν= 800 eV

700 ºC, 1 min

0º60 ºIntensity (arb. units)

Results and Discussion
We show Si 2p photoemission spectra for the 1 minannealing sample in Figs. 1 (a) and (b) at emission anglesof 0 and 60 °, respectively. The sample is free from Hfsilicide by Hf 4f photoemission spectra (Fig. 2). From Si
2p photoemission spectra, an oxide component X isdetected. Considering its binding energy, the component
X corresponds to a Si sub oxide. In addition, the intensity
ratio of the component X to the component poly-Si
decreases in the surface sensitive measurement,suggesting that the Si sub oxide exists below poly-Si
electrodes at the upper interface.
From these results, we have found that the Si sub oxide
component X exists at the upper interface before thesilicidation. Considering that silicidation starts not at thelower interface but at the upper interface, the differenceof Si oxide components at each interface can be wellrelated to silicidation. The oxide component,nonstoichiometric Si oxide (SiOx) exists at the upper(a)Si 2p hν = 800 eV

Intensity (arb. units)Experimental
The HfO2 layer was deposited on clean p-type Si (001)substrates by reactive magnetron sputtering using a Hfmetal. The thickness was estimated by the elipsometry tobe 2 nm for the HfO2 layer and 0.5 nm SiO2 interfacial
layer on Si substrates. Poly-Si electrodes of 3 nm weredeposited on HfO2 gate stacks at room temperature bymagnetron sputtering. Photoemission spectroscopy wascarried out at an undulator beam line BL-2C of the
Photon Factory in High-Energy Accelerator Research
Organization (KEK). Annealing was performed in ultrahigh vacuum (UHV) by a direct-current-flowing method
through the samples at 700 °C for each time just before
the photoemission measurements.

interface whereas stoichiometric Si oxide (SiO2) exists atthe lower interface. Therefore, the SiOx at the upperinterface can trigger silicidation. Considering the reported
results, silicidation occurs through the following reactions,(a)SiOx + (x-1)Si → xSiO↑
HfO2 + 4SiO ↑→ HfSi2 + 2SiO2 (b)(a) SiOx at the upper interface reacts with poly-Si and SiO
gas is generated. (b) SiO gas reacts with HfO2 andsilicidation may occur consequently with the SiO2formation [2]. Here, the SiOx can be formed by theoxygen atom diffusion from HfO2 to poly-Si during
annealing. Consequently, oxygen vacancies are formed inHfO2 [3].

no Hf silicide×20222018161412Binding Energy (eV)Fig. 2. Hf 4f photoemission spectra by the 700 °C
annealing for 1 min. Solid curve shows the spectrum
taken at the emission angle of 0 °. Dashed curveshows that of 60 °.
References[1] H. Takahashi et al., Appl. Phys. Lett. 87, 012903(2005).
[2] T. S. Jeon et al., Appl. Phys. Lett. 78, 368 (2001).
[3] K. Shiraishi et al., Jpn. J. Appl. Phys. 43, L1413(2004).
*
htakahashi@sr.t.u-tokyo.ac.jp