The effects of nitridation on the density of traps at SiO2/SiC interfaces near the conduction band edge were qualitatively examined using a simple, newly developed characterization method that utilizes Hall effect measurements and split capacitance–voltage measurements. The results showed a significant reduction in the density of interface traps near the conduction band edge as a result of nitridation, but the interface traps were not completely eliminated by nitridation.

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We propose another process for fabricating 4H-SiC metal-oxide-semiconductor field-effect transistors (MOSFETs) with high channel mobility. The B atoms were introduced into a SiO 2 /4H-SiC interface by thermal annealing with a BN planar diffusion source. The interface state density near the conduction band edge of 4H-SiC was effectively reduced by the B diffusion and the fabricated 4H-SiC MOSFETs showed a peak field-effect mobility of 102 cm 2 /Vs. The obtained high channel mobility cannot be explained by counter doping because B atoms act as acceptors in 4H-SiC. We suggest that the interfacial structural change of SiO 2 may be responsible for the reduced trap density and enhanced channel mobility.Index Terms-Boron passivation, channel mobility, interface state density, SiC MOSFETs.

The conduction mechanism of the leakage current of a thermally grown oxide on 4H silicon carbide (4H-SiC) was investigated. The dominant carriers of the leakage current were found to be electrons by the carrier-separation current-voltage method. The current-voltage and capacitance-voltage characteristics, which were measured over a wide temperature range, revealed that the leakage current in SiO2/4H-SiC on the Si-face can be explained as the sum of the Fowler-Nordheim (FN) tunneling and Poole-Frenkel (PF) emission leakage currents. A rigorous FN analysis provided the true barrier height for the SiO2/4H-SiC interface. On the basis of Arrhenius plots of the PF current separated from the total leakage current, the existence of carbon-related defects and/or oxygen vacancy defects was suggested in thermally grown SiO2 films on the Si-face of 4H-SiC.

We study an electron-spin-resonance (ESR) signal of carbon dangling-bond defects at 4H-SiC(0001)/SiO 2 interfaces, which we call an "interface carbon defect." The ESR signal is close to a c-axial type of the P bC centers (interfacial carbon dangling bonds) that have originally been found in porous-SiC/SiO 2 interfaces. The interface carbon defects were always formed with an areal density of 3-4 Â 10 12 cm À2 after the standard dry oxidation of 4H-SiC(0001) surfaces. They act as electron traps and decrease the amount of free electrons in the channel region, consequently reducing the field-effect mobility of Si-face 4H-SiC MOSFETs. They were eliminated by optimum post-oxidation anneals (POAs) in either NO or POCl 3 environment. Furthermore, POCl 3 POAs at 1000 C introduced a high density (1.7 Â 10 12 cm À2) of phosphorus donors into the channel region, increasing the free-carrier density as compared with the case of NO POAs.