The invention is embodied in a gas injection apparatus for injecting gases into a plasma reactor vacuum chamber having a chamber housing, a pedestal holding a workpiece to be processed, means for applying RF energy into the chamber, the gas injection apparatus having a gas supply containing an etchant species in a gas, an opening in the chamber housing, a gas feed line from the supply to the opening in the chamber housing, and gas distribution apparatus near the opening in the chamber housing, the gas feed apparatus having at least one slit nozzle facing the interior of the chamber. In a preferred embodiment, the gas distribution apparatus includes a disk member surrounded by at least one annular member with a gap therebetween comprising the slit nozzle, the disk member and annular member blocking gas flow through the opening in the chamber housing. Preferably, each of the members of the gas distribution apparatus comprises a material at least nearly impervious to attack from the etchant species. In one example, each of the members of the gas distribution apparatus comprises one of ceramic, quartz, sapphire, polyimide or anodized aluminum and the gas feed line comprises stainless steel. Preferably, each of the members has its surface polished prior to assembly of the gas distribution apparatus.