Abstract: A semiconductor manufacturing process wherein deep and narrow 0.3 micron and smaller openings are plasma etched in a dielectric layer such as doped and undoped silicon oxide. The etching gas includes at least one fluorocarbon reactant and carbon monoxide and optionally a carrier gas such as Ar. The etching process is carried out in a high density plasma reactor and is effective to etch the dielectric layer with high selectivity to the masking layer and/or a stop layer. The process is useful for etching 0.25 micron and smaller contact or via openings in forming structures such as damascene structures.