4H-SiC(0001), (000 " 1 1), and (11 " 2 20) have been directly oxidized by N 2 O at 1300 C, and metal-oxide-semiconductor (MOS) interfaces have been characterized. The interface state density has been significantly reduced by N 2 O oxidation on any face, compared to conventional wet O 2 oxidation at 1150 C. Planar n-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) fabricated on 4H-SiC(0001), (000 " 1 1) and (11 " 2 20) faces have shown effective channel mobilities of 26, 43, and 78 cm 2 /Vs, respectively. Secondary ion mass spectrometry analyses have revealed a clear pileup of nitrogen atoms near the MOS interface. The thickness of the interfacial transition layer can be decreased by N 2 O oxidation. The crystal face dependence of the interface structure is discussed. A simple consideration of chemistry indicates that NO, generated from the decomposition of N 2 O, may be a more efficient oxidant of carbon than O 2 .

4H‐SiC MISFETs with nitrogen‐containing insulators have been fabricated and characterized. Several techniques have been explored to incorporate nitrogen in the gate insulator in order to improve the density of interface states and thereby the channel mobility. The techniques are N2O‐grown oxides, the oxidation of a surface layer co‐implanted with N+ and Al+, deposited SiO2 annealed in N2O and NO, and deposited SiNx /SiO2 annealed in N2O. By optimizing the formation process of the gate insulators, MIS capacitors with N‐containing insulators have demonstrated an interface state density close to the conduction band edge below 2 × 1011 cm–2 eV–1 which is one or two orders‐of‐magni‐ tude lower than that of MOS capacitors with oxides grown in dry O2. The channel mobility of the n‐channel 4H‐SiC(0001) MISFETs with N‐containing insulators is increased to about 30 cm2/Vs. In addition, an even higher channel mobility of 50 cm2/Vs has been realized by utiliz‐ ing N‐containing insulators adequately processed on the 4H‐SiC (000$ \bar 1 $) face. From the experimental results, the dominant scattering mechanisms in SiC MISFETs have been identified; Coulomb scattering and electron trapping at interface states dominate the channel mobility in SiC MOSFETs with thermally‐grown and deposited SiO2. The application of N‐containing insulators to p‐channel 4H‐SiC MIS devices is also discussed. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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