Negative Gate Bias TDDB evaluation of n-Channel SiC Vertical Power MOSFETs

With the steep expansion of the n-type 4H-SiC power metal-oxide-semiconductor field-effect transistor (MOSFET) market space, gate oxide reliability is gaining more and more attention. Although there exist several reports dealing with the bias temperature instability (BTI) under both positive and negative gate biases, gate oxide lifetime evaluations predominantly focus on positive gate bias time-dependent dielectric breakdown (TDDB) stresses for n-channel SiC MOSFETs. In this work we address that gap. From the negative gate bias TDDB data measured at 175 °C and at a gate oxide electric field of about 4 MV/cm, an intrinsic lifetime of 1E8 hours has been predicted, which closely matches with the results obtained from similar devices under positive gate stress. Also, in this work the correlation between failure location in a MOSFET unit cell and the failure signatures during TDDB stress have been established, and an explanation from a device physics standpoint has been provided. The identification of the failure location in the unit cell from in-situ gate leakage data without the need of physical failure analysis can turn out to be key during the early phase of a new process development activity.