In this paper the effects of 5 MeV proton irradiation on nitrided SiO₂/4H-SiC metal–oxide–semiconductor (MOS) capacitors are studied in detail and the related mechanisms are revealed. The density of interface states (Dit) is increased with the irradiation doses, and the annealing response suggests that the worse of Dit is mainly caused by displacement effect of proton irradiation. However, the X-rays photoelectron spectroscopy (XPS) measurement shows that the quantity proportion of breaking of Si≡N induced by displacement is only 8%, which means that the numbers of near interface electron traps (NIETs) and near interface hole traps (NIHTs) are not significantly changed by the displacement effect. The measurements of bidirectional high frequency (HF) C-V characteristics and positive bias stress stability show that the number of un-trapped NIETs and oxide electron traps decreased with increasing irradiation doses because they are filled by electrons resulted from the ionization effect of proton irradiation, benefiting to the field effective mobility (μ_FE) and threshold voltage stability of metal–oxide–semiconductor field-effect transistors (MOSFETs). The obviously negative shift of flat-band voltage (V_FB) resulted from the dominant NIHTs induced by nitrogen passivation capture more holes produced by ionization effect, which has been revealed by the experimental samples with different nitrogen content under same irradiation dose.

The effects of 5 MeV proton irradiation on ON-state characteristics of 1200 V 4H-SiC VDMOSFETs are investigated in this paper, and related mechanisms have been revealed by the analysis of their test structure of ohmic contacts, lateral nMOSFETs and MOS capacitors simultaneously fabricated on same wafer. The results show that the threshold voltage (VTH) decreases obviously with increasing irradiation doses because the dominant hole traps induced by nitrogen passivation might capture more holes produced by the ionization effect of proton irradiation, resulting in the generation of net positive charges nearby the SiO2/4H-SiC interface. The interface trap density (Dit) extracted by subthreshold swing increases but field effective mobility (μFE) is improved with increasing irradiation doses. The un-trapped near interface electron traps (NIETs) are reduced by the ionization effect of proton irradiation, which could be beneficial to the improvement of μFE. And after the maximum irradiation dose of 1×1014 p/cm2 the VDMOSFET fails in the ON-state capability. Before it fails, the ON-state resistivity (RON) firstly decreases and then increases with the increase of irradiation dose. The deterioration of the resistance of lightly doped drift region (RD) and the resistance of JFET region (RJFET) caused by the displacement effect of proton irradiation covers up the improvement of the channel resistance (RCH) with increasing irradiation doses, finally leading to the failure of the VDMOSFET at the maximum proton irradiation dose.