Plasma damage and photo-annealing effects of thin gate oxides and oxynitrides during O-2 plasma exposure

Plasma-induced damage effects of oxides and oxynitrides are studied using metal-oxide-semiconductor (MOS) test capacitors in an O-2 plasma environment inside a capacitive-coupled parallel plate RF etcher, Damage to both covered and sidewall-exposed samples are compared, As expected, it was found that as the exposure time was increased, more damage to the oxide was observed, Furthermore, N2O-samples showed better immunity to O-2-plasma damage than the thermally grown O-2 samples during O-2 plasma exposure, However, the edge-intensive sidewall-exposed structures showed surprisingly less damage than the fully covered structures after a fixed plasma exposure time. This reduced damage effect for the sidewall-exposed structures is believed to be due to an in situ annealing as the result of the photoelectron injection by low-energy UV light interacting with the substrate, The in situ annealing does not occur in the fully covered structure since the low-energy UV light is blocked by the thick polysilicon gate. The results indicate that plasma damage evaluation using fully covered capacitors alone cannot be used to predict the actual damage in CMOS integrated circuits where there are almost always exposed thin oxide structures.