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

4C, 15C, 18B/2004G059

Ordered Structure in the Thermal Oxide Layer
on Silicon-on-Insulator Substrates
Takayoshi SHIMURA*1, Eiji MISHIMA1, Kiyoshi YASUTAKE1, Masataka UMENO2
Graduate School of Engineering, Osaka Univ., 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
2
Faculty of Engineering, Fukui University of Technology, 3-6-1 Gakuen, Fukui 910-8585, Japan
1

Introduction
It is widly accepted that the thermal oxide layer on theSi surface has amorphous structure and some crystalline
oxides exist just close to the interface, although several
structural models are still inconsistent with each other.
Recent studies using high-resolution transmission
electron microscope basically support the structuralmodel, in which any crystalline oxides are not observed in
the region far from the interface [1].
However, we have been proposing that the thermaloxide layer are not simple amorphous, but has a kind ofordered structure not only close to the interface but also
throughout the oxide layer, having an epitaxial relation
with the Si substrate [2]. This structural model is based on
the results of the x-ray diffraction experiments. In thisreport we show the experimental result for the thermaloxide layer on silicon-on-insulator (SOI) substrates.

Experimental
The SOI layer of 100 nm thickness is oxidized at
950 °C in dry O2. The thickness of the oxide layer is 25
nm. X-ray diffraction experiments using synchrotron
radiation were performed on BL4C of Photon Factory(KEK) by employing a four-circle diffractometer with anSi(111) crystal analyzer. The wavelength was chosen to be
0.154 nm.

ResultsThe ordered structure was found in the thermal oxide
layer on the SOI layer. Because of the existence of anunintentional misorientation between the SOI layer andthe Si substrate, we can observe x-rays diffracted by theSOI layer separately from that by the substrate. In Fig. 1
the intensity distribution of the CTR scattering around the111 Bragg point of the SOI layer is shown. We see thatthe intensity distribution of the CTR scattering itself has
the thickness fringe related to the thickness of the SOIlayer. The extra peak of the ordered oxide is observed at1 1 0.47 as in the case of the oxide layer on the bulk wafer.
The inset of Fig. 1 shows the enlargement around theextra peak. We see the Laue-function-like oscillation
pattern of which period corresponds to the inverse of theoxide thickness, together with the fringe for the SOI layer.
This result is additional evidence indicating the existenceof the ordered oxide having the epitaxial relation with theparent Si crystal.

References[1] N. Ikarashi et al., Phys. Rev. B62, 15989 (2000).
[2] K. Tatsumura et al., Phys. Rev. B69, 085212 (2004).
* shimura@mls.eng.osaka-u.ac.jp101
Intensity [arb.units]

Intensity [arb.units]

104

102

100

10-1
0.4

0.45

0.5

0.55

11L [a*]10010-2
0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0
1.1
1.2
1.3
1.4
1.5
1.6
11L [a*]Fig. 1 Intensity distribution of the CTR scattering around the 111 Bragg point from the bonded SOI layer with thethermal oxide layer of 25 nm thickness. Inset shows the enlargement around the extra peak.

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