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Unformatted text preview: 504 IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 46, NO. 3, MARCH 1999 Effects of Wet Oxidation/Anneal on Interface Properties of Thermally Oxidized SiO /SiC MOS System and MOSFET’s Hiroshi Yano, Fumito Katafuchi, Tsunenobu Kimoto, and Hiroyuki Matsunami, Member, IEEE Abstract— Effects of wet atmosphere during oxidation and anneal on thermally oxidized p-type and n-type MOS interface properties were systematically investigated for both 4H- and 6H- SiC. Deep interface states and fixed oxide charges were mainly discussed. The wet atmosphere was effective to reduce a negative flatband shift caused by deep donor-type interface states in p-type SiC MOS capacitors. Negative fixed charges, however, appeared near the interface during wet reoxidation anneal. In n- type SiC MOS capacitors, the flatband shift indicated a positive value when using wet atmosphere. The relation between interface properties and characteristics of n-channel planar 6H-SiC metal- oxide-semiconductor field effect transistors (MOSFET’s) was also investigated. There was little relation between the interface properties of p-type MOS capacitors and the channel mobility of MOSFET’s. The threshold voltage of MOSFET’s processed by wet reoxidation anneal was higher than that of without reoxidation anneal. A clear relation between the threshold voltage and the channel mobility was observed in MOSFET’s fabricated on the same substrate. Index Terms— Deep interface states, fixed oxide charges, inter- face, MOS, MOSFET’s, reoxidation anneal, silicon carbide, wet oxidation. I. INTRODUCTION S ILICON CARBIDE (SiC) is a promising semiconductor for high-power, high-temperature, and high-frequency de- vices because of its superior properties such as wide bandgap, high breakdown field, high saturation electron drift velocity, and high thermal conductivity. For the aspect of device pro- cesses, SiC has an advantage of both n- and p-type conduction in a wide range by either in situ doping ,  or selective ion implantation , . One of the most important advantages of SiC over other wide bandgap semiconductors is that SiC can be thermally oxidized to form high-quality SiO like Si : metal- oxide-semiconductor field effect transistors (MOSFET’s) can be made on SiC. Nowadays, SiC MOSFET’s have been intensively inves- tigated by many groups –. However, their excellent characteristics expected from SiC properties have not been Manuscript received November 6, 1998; revised November 16, 1998. This work was supported in part by a Grant-in-Aid for Specially Promoted Research from the Ministry of Education, Science, Sports and Culture of Japan and by Kyoto University Venture Business Laboratory. The review of this paper was arranged by Editor J. W. Palmour....
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