Novel Gate Oxide Process for Realization of High Threshold Voltage in 4H-SiC MOSFET

We found that threshold voltage (Vth) of a 4H-SiC MOSFET increases drastically by performing low temperature wet oxidation after nitridation in a gate oxide process. The increment of Vth depends on the wet oxidation conditions. Wet oxidation increases the interface trap density (D-it) at deep level of SiC bandgap and decreases positive charge density inside the gate oxide layer. The amount change of the interface traps and the positive charges in the gate oxide makes Vth higher without a decrease in the channel mobility. We improved the trade-off between Vth and effective carrier mobility (mu(eff)) in the MOSFET channel, and realized a low specific on-resistance (R-on,R-sp) SiC-MOSFET with a rated Vth over 5 V by using the newly developed process.