Comparison between oxidation processes used to obtain the high inversion channel mobility in 4H-SiC MOSFETs

Abstract

In this work two oxidation methods aimed at improving the silicon face 4H-SiC/SiO2 interface are compared. One is an oxidation in N2O performed in a quartz tube using quartz sample holders and the other is a dry oxidation performed in an alumina tube using alumina sample holders. In n-type metal oxide semiconductor (MOS) capacitors the interface state density near the SiC conduction band edge is estimated using capacitance–voltage (C–V) and thermal dielectric relaxation current (TDRC) measurements. N-channel metal oxide semiconductor field effect transistors (MOSFETs) are characterized by current–voltage (I–V) techniques and the inversion channel mobility is extracted. It is shown that the high inversion channel mobility (154 cm2 V−1 s−1) seen in samples oxidized using alumina correlates with a low interface trap density (3.6 × 1011 cm−2). In the case of N2O oxidation the mobility is lower (24 cm2 V−1 s−1) and the interface trap density is higher (1.6 × 1012 cm−2). Room temperature C–V measurements are of limited use when studying traps near the conduction band edge in MOS structures while the TDRC measurement technique gives a better estimate of their density.