Abnormal Behavior of Longitudinal Optical Phonon in Silicon Dioxide Films on 4H–SiC Bulk Epitaxial Substrate Using Fourier Transform Infrared (FT-IR) Spectroscopy

Abstract

We report the abnormal behavior of longitudinal optical (LO) phonon in a silicon dioxide (SiO2) film on a 4H-SiC bulk epitaxial substrate using an attenuated total reflection (ATR) technique. The peak frequency of the LO phonon in the ATR spectrum was observed at around 1165 cm(-1) and red-shifted by approximately 92 cm(-1) relative to that at the grazing incidence (40°), whereas the peak frequency of the transverse optical (TO) phonon in the ATR spectrum agreed well with that at the grazing incidence. Furthermore, the peak frequency of the TO phonon hardly depends on change in the incident angle and thickness, suggesting that the microstructure of the sample is homogeneous within a thickness of 100 nm. On the other hand, we found that the microstructure of the sample was inhomogeneous within a thickness less than 5 nm. Fourier transform infrared (FT-IR) spectroscopy provides us with a large amount of data on microstructures in the SiO2 films on a 4H-SiC substrate.

Characterization of Inhomogeneity in Silicon Dioxide Films on 4H-Silicon Carbide Epitaxial Substrate Using a Combination of Fourier Transform Infrared and Cathodoluminescence Spectroscopy

“…We prepared two sets of SiO 2 films, which were thermally grown on commercially available 4H-SiC epitaxial and on bulk 4H-SiC epitaxial substrates to measure the transparent FT-IR spectra of SiO 2 films on 4H-SiC substrates. First, commercially available epitaxial layers (approximately 100 μm thick) on a 4° off-axis 4H-SiC (0001) Si-face substrate were thermally oxidized in dry oxygen gas (O 2 ) at 1150 °C and then annealed in Ar ambient at 1300 °C under the same condition as in Yoshikawa and colleagues 15,17 (samples 1-5). In Yoshikawa et al, 15 we measured a transparent FT-IR spectra of sample 5 to assign the optical phonons observed.…”

“…We concluded that the asymmetric modes located between 1110 and 1250 cm −1 were due to the upper and lower branches of surface phonon polaritons (SPPs). 15 Furthermore, we divided the asymmetric modes located between 1110 and 1250 cm −1 into the two peaks with Lorentzian line shapes and suggested that the two peaks were assigned to the upper and lower branches of SPPs at the air–SiO 2 , and SiO 2 –4H-SiC interfaces, respectively. 15…”

“…In a previous paper, 15 we reported on the abnormal behavior of LO phonons in a SiO 2 film on a 4H-SiC bulk epitaxial substrate using an ATR technique. The peak frequency of the LO-like phonon with an asymmetric line shape in the ATR spectrum was observed at around 1165 cm −1 and red-shifted by approximately 92 cm −1 relative to that at the grazing incidence (40°).…”

Stress Characterization of the Interface Between Thermal Oxide and the 4H-SiC Epitaxial Layer Using Near-Field Optical Raman Microscopy

“…1,2 Fourier transform infrared (FT-IR) spectroscopy is a powerful technique for studying chemical-bonding structures within silicon-oxide films. [3][4][5] In a prior study, 6 FT-IR measurements were measured along with cathodoluminescence (CL) spectra of thermal oxide (SiO 2 ) films on 4H-SiC substrates. Findings of the said study demonstrated TO phonon to be blueshifted by approximately 5 cm À1 owing to reduction in oxide-layer thickness from 65 nm to 10 nm.…”

FTIR-ATR Study on Near-Interface Structure of Thermal Oxides on 4H-SiC Substrates

“…The (0001) and (000-1) are the widely studied crystal faces of 4H-SiC, and the MOS capacitors made on those faces often show different electrical characteristics [6]. The FTIR-ATR studies have been reported for thermally-grown films on SiC by a few groups [7,8], however, the near-interface structure has not been investigated in detail so far.…”