Effects of 5 MeV Proton Irradiation on 1200 V 4H-SiC VDMOSFETs ON-State Characteristics

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 (V
_TH
) 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 SiO
₂
/4H-SiC interface. The interface trap density (Dit) extracted by subthreshold swing increases but field effective mobility (μ
_FE
) 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 μ
_FE
. And after the maximum irradiation dose of 1 × 10
¹⁴
p/cm
²
the VDMOSFET fails in the ON-state capability. Before it fails, the ON-state resistivity (R
_ON
) firstly decreases and then increases with the increase of irradiation dose. The deterioration of the resistance of lightly doped drift region (R
_D
) and the resistance of JFET region (R
_JFET
) caused by the displacement effect of proton irradiation covers up the improvement of the channel resistance (R
_CH
) with increasing irradiation doses, finally leading to the failure of the VDMOSFET at the maximum proton irradiation dose.