title: Characterization of Thermal Oxides on 4H-SiC Epitaxial Substrates Using Fourier-Transform Infrared Spectroscopy.
abstract: Fourier transform infrared (FT-IR) spectra were measured for thermal oxides with different electrical properties grown on 4H-SiC substrates. The peak frequency of the transverse optical (TO) phonon mode was blue-shifted by 5 cm-1as the oxide-layer thickness decreased to 3 nm. The blue shift of the TO mode indicates interfacial compressive stress in the oxide. Comparison of data for the oxide on a SiC substrate with that for similar oxides on a Si substrate implies that the peak shift of the TO mode at the SiO2/SiC interface is larger than that of SiO2/Si, which suggests that the interfacial stress for the oxide on the SiC substrate is larger than that on the Si substrate. For the SiO2/SiC interfacial region (<3 nm oxide thickness), despite the fact that the blue shift of the TO modes becomes larger while approaching the oxide/SiC interface, the peak frequency of the TO modes red-shifts at the oxide/SiC interface. The peak-frequency shift of the TO mode for the sample without post-oxidation annealing was larger than that for the samples post-annealed in a nitric oxide atmosphere. The channel mobilities are correlated with the degree of shift of the TO mode when the oxide thickness is <3 nm. It appears that the compressive stress at the SiO2/SiC interface generates silicon suboxide components and weakens the Si-O bonds. As the result, the TO mode was red-shifted and the oxygen deficiency increased to relax the compressive stress in the oxide with <3 nm thickness. Fourier transform infrared spectroscopy measurements provide unique and useful information about stress and inhomogeneity at the oxide/SiC interface.
authors.affiliation: 1 Toray Research Center Inc., Otsu, Shiga, Japan.
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Seki
authors.affiliation: 1 Toray Research Center Inc., Otsu, Shiga, Japan.
authors.forename: Masanobu
authors.initials: M
authors.lastname: Yoshikawa
authors.affiliation: 2 Department of Electronic Science and Engineering, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto, Japan.
authors.forename: Takuma
authors.initials: T
authors.lastname: Kobayashi
authors.affiliation: 2 Department of Electronic Science and Engineering, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto, Japan.
authors.forename: Tsunenobu
authors.initials: T
authors.lastname: Kimoto
authors.affiliation: 3 Department of Chemistry, School of Science and Technology, Kwansei Gakuin University, Sanda, Hyogo, Japan.
authors.forename: Yukihiro
authors.initials: Y
authors.lastname: Ozaki
keywords: 4H-SiC; ATR; FT-IR; Fourier transform infrared spectroscopy; TO phonon; attenuated total reflection; silicon dioxide films