Nitrogen implantation to improve electron channel mobility in 4H SiC MOSFET

Normally off 4H-SiC MOSFET devices have been fabricated on p-type semiconductor and electrically characterized at different temperatures. A gate oxide obtained with nitrogen ion implantation performed before the thermal oxidation of SiC has been implemented in n-channel MOSFET technology. Two samples with a nitrogen concentration at the SiO2/SiC interface of 5x1018 and 1.5x1019 cm-3 and one un-implanted have been manufactured. The sample with the highest N concentration at the interface presents the highest channel mobility and the lowest threshold voltage. For increasing temperature, in all the samples the threshold voltage decreases and the electron channel mobility increases. The latter attains a maximum value of about 40 cm2/Vs at 200 °C for the sample with the highest N concentration. These trends are explained by the reduction of interface electron traps in the upper half of the band-gap towards the conduction band edge. These results demonstrate that N implantation can be effectively used to improve the electrical performances of a n-type surface channel 4H-SiC MOSFET.