Degradation of gate oxide breakdown characteristics by electrostatic and radiation damage during plasma processing

The electrostatic and radiation damage incurred during plasma processing is studied using MOS (metal-oxide-semiconductor) capacitors with various sizes of surface metal pad attached to the gate electrode as charge collectors. Oxides grown in a wet ambient show a sharper breakdown distribution and a higher resistance to plasma damage than oxides grown in a dry ambient. Residual trapped holes near the polysilicon-gate/SiO₂ interface, which cause anomalous leakage currents in negative gate IV characteristics, may be an indication of the latent damage from electrostatic charging. These trapped charges are believed to arise from hole tunneling during plasma exposure due to electrostatic induced positive bias on the gate electrode. Breakdown characteristics are significantly degraded when electrons are injected from the polysilicon gate as opposed to injection from the silicon substrate. The most prominent effect of the electrostatic damage during plasma processing is the degradation in breakdown voltages of defective oxide.