Abstract: A method is provided for reducing contact resistances in semiconductors. In the use of fluorocarbon plasmas during high selectively sub-quarter-micron contact hole etching, with the silicon dioxide(SiO2)/silicon nitride(Si3N4)/silicide(TiSix) layers, polymerization effects have been discovered to be crucial. The process includes using a high etch selective chemistry, to remove SiO2 first, then switching to another chemistry with high selectivity of Si3N4-to-TiSix. To obtain good etch selectivity of SiO2-to-Si3Nx, fluorocarbon plasmas containing high C/F ratio are employed. This results in the information of reactive unsaturated polymers which stick easily to contact sidewalls and bottoms. Fluorine from the polymer was discovered to severely degrade the etch selectivity of Si3N4-to-TiSix. Different polymer removing methods to restore etch selectivity of Si3N4-to-TiSix, are provided which can be applied to any highly selective etching of oxide versus nitride.