MOS Interface Properties and MOSFET Performance on 4H-SiC{0001} and Non-Basal Faces Processed by N 2 O Oxidation
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MOS Interface Properties and MOSFET Performance on 4H-SiC{0001} and Non-Basal Faces Processed by N2O Oxidation T. Kimoto, Y. Kanzaki, M. Noborio, H. Kawano, and H. Matsunami Department of Electronic Science and Engineering, Kyoto University Katsura, Nishikyo, Kyoto 615-8510, Japan ABSTRACT 4H-SiC(0001), (000-1), and (11-20) have been directly oxidized by N2O at 1300oC, and the MOS interfaces have been characterized. The interface state density has been significantly reduced by N2O oxidation on any face, compared to conventional wet O2 oxidation at 1150oC. Planar n-channel MOSFETs fabricated on lightly-doped 4H-SiC(0001), (000-1) and (11-20) faces have shown an effective channel mobility of 26, 43, and 78 cm2/Vs, respectively. The mobility decreased with increasing the doping concentration of p-body. SIMS analyses have revealed a clear pile-up of nitrogen atoms near the MOS interface. The thickness of interfacial SiCxOy layer can be decreased by utilizing N2O oxidation. The crystal face dependence of interface structure is discussed. INTRODUCTION Although silicon carbide (SiC) MOSFETs are recognized as ideal power switches, SiC MOSFETs have still suffered from low effective channel mobility. In recent years, post-oxidation nitridation in an NO ambience is widely used to improve SiO2/4H-SiC(0001) interface properties and thereby to increase effective channel mobility of MOSFETs [1,2]. Direct oxidation with N2O has been also proposed as an alternative to form the “nitrided” MOS interface for the safety reason [3]. Recent investigations have revealed that wet-O2 oxidized 4H-SiC(000-1) [4] and non-basal faces such as (11-20) [5] possess much potential to further improve the quality of MOS interface. In this study, the interface state density and MOSFET performance have been investigated on 4H-SiC(0001), (000-1), and (11-20) by using N2O oxidation. Effects of doping concentration in the p-body on MOSFET performance, which is important for practical device development, are discussed. The distribution of nitrogen and carbon concentrations in the MOS structure and its correlation with the MOS interface quality is presented. EXPERIMENTS Epitaxial layers with a thickness of about 5 µm were grown by chemical vapor deposition (CVD) on 8o off-axis 4H-SiC(0001), (000-1), and on-axis (11-20) [6]. After the RCA cleaning, thermal oxidation was carried out at 1300°C in an N2O (diluted in N2) ambience, followed by post-oxidation annealing (POA) at 1300°C in N2 for 30 min. The typical oxide thickness was 70 nm. The crystal face dependence of oxidation rate was similar to that by O2 oxidation: The oxidation is the fastest on (000-1) and slowest on (0001), and that on (11-20) in between. In some experiments, conventional wet O2 oxidation at 1150°C was used for comparison. To assess the interface properties, MOS capacitors were fabricated on n-type epilayers. The donor concentration was 1-2×1016 cm-3 for (0001) and 7-9×1015 cm-3 for (000-1), and 6-7×1015
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cm-3 for (11-20). The interface state density and effective fixed ch
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