A process for passivating a carbon-based hard mask, for example, of hydrogenated amorphous carbon, overlying an oxide dielectric which is to be later etched according to the pattern of the hard mask. After the hard mask is photo lithographically etched, it is exposed to a plasma of a hydrogen-containing reducing gas, preferably hydrogen gas, and a fluorocarbon gas, preferably trifluoromethane. The substrate can then be exposed to air without the moisture condensing in the etched apertures of the hard mask.