Ultra-thin silicon-dioxide breakdown characteristics of MOS devices with n + and p + polysilicon gates

In this work we investigate the effect of the gate material on the breakdown characteristics of ultra-thin silicon dioxide films at low voltages (<6 V). When MOS capacitors are stressed with a positive gate voltage, the charge to breakdown and time to breakdown at a fixed oxide-voltage drop are significantly smaller in p+ polysilicon-gate capacitors than in n+ polysilicon-gate capacitors. The results are interpreted in terms of a simple model of hole tunneling resulting from hot-hole generation in the anode by hot electrons entering from the silicon dioxide. Extrapolation of high-voltage-breakdown lifetime measurements for relatively thick-oxide devices to low voltages may be complicated by this mechanism.