Photon Factory Activity Report 2004 #22 Part B (2005)
Surface and Interface

2C/2002S2-002

Interfacial reaction of polycrystalline-Si /HfO2/Si gate stacks with annealingstudied by photoemission spectroscopy
Haruhiko TAKAHASHI1*, Satoshi TOYODA1, Jun OKABAYASHI1, Hiroshi KUMIGASHIRA1,
1
2
2
2
2
Masaharu OSHIMA , Kazuto IKEDA , Guo-Lin LIU , Ziyuan LIU , and Koji USUDA
1The University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan
2STARC, Kohoku-ku, Kanagawa 222-0033, Japan
Introduction
For continuous improvements in ultra-large-scale
integrated (ULSI) device performance, the device size has
been shrinking following Moore’s law. In the sub-nm
scale of the gate dielectrics, the current processes using
SiO2 reach the limitation due to the direct tunnelingleakage current. Recently, the alternative high dielectric
constant (high-k) materials such as Al2O3, ZrO2, Y2O3, andHfO2 have been widely investigated. HfO2 is one of themost promising materials because of its thermal stability,
wide band gap, and high dielectric constant. In the current
Si technology, polycrystalline-Si (poly-Si) is used as agate electrode. One of the current problems for HfO2
application is a thermal stability at the interface between
poly-Si electrodes and high-k dielectrics during activation
annealing of dopants. In order to improve device
performances, chemical reactions at the interface have to
be clarified explicitly.

that the Hf silicide is formed at the “upper interface”
between poly-Si and HfO2. On the contrary, the intensity
ratio decreases in the surface-sensitive measurements by
the annealing at 750 °C. This is because the silicidation
promotes into the lower interface. Peak shifts in the HfO2component by 750 °C annealing are explained by thechange of the interface component from Hf silicate to Hfsilicide and the band offsets are also changed. By theannealing at 800 °C, the HfO2 component completely
disappears and only the Hf-silicide components remain.
In the case without the poly-Si electrodes, the Hf-silicide
formation occurred by the annealing at as hightemperature as 900 °C in previous reports[1,2]. These
results indicate that the poly-Si electrodes drastically
influence the silicidation temperature at the “lowerinterface” between HfO2 and Si substrate.
Hf 4f hν = 800 eV0º60 ºExperimental
The HfO2 layer was deposited on clean p-type Si(001) substrates by reactive magnetron sputtering using aHf metal. The thickness was estimated by the elipsometry
to be 2 nm for the HfO2 layer and 0.5 nm for theinterfacial Hf-silicate layer on Si substrates. Poly-Sielectrodes of 3 nm were deposited on HfO2 gate stacks atroom
temperaturebymagnetronsputtering.
Photoemission spectroscopy was carried out at anundulator beam line BL-2C of the Photon Factory inHigh-Energy Accelerator Research Organization (KEK).
Annealing was performed in ultra high vacuum (UHV) by
a direct-current-flowing method through the samples for
10 min at each temperature before the photoemission
measurements.
Results and Discussion
Hf 4f photoemission spectra are shown in Fig. 1.
Angular dependence to increase the surface sensitivity isalso investigated by changing the emission angle fromsurface normal to 60 °. The components appearing at thebinding energy of 18 eV with spin-orbit splitting arederived from HfO2. By the annealing at 700 °C, a newcomponent appears at the binding energy of 14.5 eV,
which can be assigned as the Hf-silicide component. The
intensity ratio of the Hf-silicide component to the HfO2component
increases
bythesurface-sensitive
measurements in the emission angle of 60 °, suggesting

Intensity (arb. units)

800 ºC750 ºC×10700 ºC
650 ºC
600 ºC
as-etched
22 20 18 16 14 12Binding Energy (eV)Fig. 1. Hf 4f photoemission spectra depending on theannealing temperature. Solid curves show the spectra
taken at the emission angle of 0 °. Dashed curves
show those of 60 °.
References[1] S. Toyoda et al., Appl. Phys. Lett. 84, 2328 (2004).
[2] J. H. Lee, Thin Solid Films 472, 317 (2004).
*

htakahashi@sr.t.u-tokyo.ac.jp

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