The influence of the N+ source region on parasitic PNP conduction in integrated N-Channel DMOS

The physics of substrate hole injection during forward biasing of the P-body to N-epi antiparallel diode in integrated N-channel DMOS is explored. The N+ source region is shown to reduce the effective beta of the parasitic substrate PNP by collecting back injected electrons in the P-body region. By shunting the main anode current, the parasitic NPN provides a 1.5 to 2/spl times/ reduction in substrate hole collection. Conductivity modulation of the N-epi drain region is found to maintain the beneficial effects of this NPN through compensating improvements in the emitter injection efficiency at high anode currents. Recombination in the P+ region is shown to be negligible except at high bias conditions.