Characterization of the Interfaces between IV-IV Semiconductors and Ultra-Thin Oxide films

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We have used spectroscopic ellipsometry, together with photoelectron spectroscopy, to investigate the interfaces between the oxide film and SiC, structural changes in the interfaces by various kinds of heat treatment after the oxide film formation, and the correlation with their electrical properties, in order to search appropriate oxidation process good for SiC MOSFETs.We have developed in-situ spectroscopic ellipsometry system to acquire the knowledge for clarifying the formation process of ultra-thin oxide films on SiC and microstructure of the interfaces. It is found that the composition of the oxide film formed in the initial stage of oxidization is different from that of stoichiometric SiO_2 and that the refractive indices of the interface layers, which are larger than that of SiC and SiO_2, decrease with heat treatment. In order to make clear the relation between the refractive indices of the interfaces and interface state density, we have carried out spectroscopic ellipsometry … More and C-V measurements for the SiC MOS structures whose interface state density is increased by gamma ray irradiation. We have found that the refractive indices of the interface layers increase with gamma ray irradiation, which suggest that the refractive indices obtained by spectroscopic ellipsometry are closely related to the interface state density, which affects the channel mobility in SiC MOSFET. Angle-resolved x-rays photoemission spectroscopy and ultraviolet photoemission spectroscopy were performed to clarify the change of composition and bonding state at the oxide/SiC interfaces by heat treatment. In addition, we have used micro infrared reflection spectroscopy to characterize the electrical properties of SiC bulk crystals and demonstrated that the distribution of the career concentration and mobility in SiC wafers can be 〓〓〓〓sured nondestructively without electric contacts.This research project brings about a better understanding of the structures of oxide/SiC interfaces and reveals that spectroscopic ellipsometry is an excellent characterization technique and is applicable to monitoring tool during device processes. Less