Effects of Oxide-Fixed Charge on the Breakdown Voltage of Superjunction Devices

摘要

Superjunction devices may employ oxide layers for termination and for isolating adjacent pillars. Fixed charges present in these oxide layers are shown to have the following influence on the device breakdown voltage $V_{rm br}$. The effect of a positive fixed charge is equivalent to an increase in the n-pillar charge. The resulting charge imbalance degrades $V_{rm br}$, and can be compensated either by increasing the p-pillar doping or by decreasing the n-pillar doping by an amount $approx!(hbox{1.2}N_{rm fT} + hbox{4}N_{rm fI})/(hbox{pillar width})$, where $N_{rm fT}$ and $N_{rm fI}$ are the fixed charges in the termination and isolation oxides, respectively. Contrary to expectation, the $V_{rm br}$ of such compensated devices can be significantly higher than that of a balanced superjunction of the same doping level without fixed charge, due to the uniform lateral depletion effect of the fixed charge.