IRAS Analysis of the Early Stage of Thermal Oxidation on a SiC Surface
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IRAS Analysis of the Early Stage of Thermal Oxidation on a SiC Surface
Tamotsu Jikimoto, Hidekazu Tsuchida, Isaho Kamata, and Kunikazu Izumi Yokosuka Research Laboratory, Central Research Institute of Electric Power Industry, 2-6-1 Nagasaka, Yokosuka, Kanagawa 240-0196, Japan. ABSTRACT The structure of thermal oxide film thinner than 2nm on a SiC surface was investigated using in-situ infrared reflection absorption spectroscopy (IRAS). In the case of oxide films on 6H-SiC(0001), the peak frequencies of the TO mode (≈ 1050 cm-1) of the Si-O-Si stretch vibration shifts toward lower wave number with decreasing oxide thickness in the range of 0.2nm to 2nm and shift toward a higher frequency as the growth temperature rises. The LO mode (≈ 1250 cm-1) of the Si-O-Si stretch vibration remains almost constant with the increase in oxide thickness from 0.2 nm to 2 nm. These results indicate that there is a considerable difference in the structure near the interface between a thermally grown oxide layer formed on SiC and one formed on Si.
INTRODUCTION SiC is an attractive semiconductor material for high-power, low-loss, and high-temperature power electronics apparatus. SiC power MOSFET in particular is the most promising for use in high-voltage and low-loss devices. Although SiC is a well known material capable of forming SiO2 by thermal oxidation like Si, SiC has unique oxidation characteristics such as a significant difference in thermal oxidation rate between the (0001) Si-face and (0001) C-face [1]. Details of the thermally grown SiO2 structure near the SiO2/SiC interface however are not fully understood. Interface state densities at the SiO2/SiC interface remain approximately 1-2 orders of magnitude higher than those typically obtained on SiO2/Si interfaces, and channel mobility of SiC-MOSFETs is low. Furthermore, it has been reported that Si4C4-xO2 [2] or carbon cluster [3, 4], or a thin C [5] exists at the SiO2/SiC interface. To make SiC devices, we need to control the electrical properties of the SiO2 layer through oxidation processes. To control the electrical properties of SiO2 film on SiC, it is important to understand the relationship between the structure of the SiO2/SiC interface and these electrical properties. In this study, RAS spectra from thermally grown oxide films on 6H-SiC are investigated in order to clarify the structure of the SiO2/SiC interface.
EXPERIMENTS The FT-IR spectrometer used in the study was a JEOL WINSPEC 100, and the detector used HgCdTe detector. The optics of the spectrometer was purged using N2. Measurement conditions were as follows: the angle of incident light on the sample was 80 degrees; the spectra were recorded at resolution of 4cm-1; and scanning was carried out 128-512 times to
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obtain the spectra. Only p-polarized IR light was used. Background spectra were taken prior to fabrication oxide layers. In general, to obtain infrared absorption data as a function of oxide thickness, samples are thinned in buffered HF acid solution. However, in this study a series of the o
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