Influence of gate oxide quality on plasma process-induced charging damage in ultra thin gate oxide

The correlation between the gate oxide quality and the plasma process-induced charging damage is studied for metal-oxide-semiconductor (MOS) devices with gate oxide thickness of 1.9-3 mm. It is found that plasma charging damage of ultra thin oxide strongly depends on its initial oxide quality. The ultra thin oxide of around 2 nm thick is not always free from plasma charging damage, if the fabrication process other than the plasma process is not optimized. A mechanism of the enhanced plasma charging damage due to gate electrode formation process is proposed. If defects exist in the oxide, these defects become weak paths for the injected current during the plasma process. Thus, current density at the defects becomes high and oxide breakdown occurs even when the oxide is as thin as 2 nm, in which current conduction by direct tunneling dominates.