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

In this work two oxidation methods aimed at improving the silicon face 4H-SiC/SiO₂ interface are compared. One is an oxidation in N ₂O 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 × 10 ¹² 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.