Plasma reactor with enhanced plasma uniformity by gas addition, and

Abstract

The invention improves etch uniformity across a silicon wafer surface in an RF plasma etch reactor. In a first aspect of the invention, etch uniformity is enhanced by reducing the etchant species (e.g., Chlorine) ion and radical densities near the wafer edge periphery without a concomitant reduction over the wafer center, by diluting the etchant (Chlorine) with a diluent gas which practically does not etch Silicon (e.g., Hydrogen Bromide) near the wafer edge periphery. In a second aspect of the invention, etch rate uniformity is enhanced by more rapidly disassociating Chlorine molecules over the center of the wafer to increase the local etch rate, without a concomitant hastening of Chlorine dissociation near the wafer periphery, by the introduction of an inert gas over the wafer center. In a third aspect of the invention, etch rate uniformity is enhanced by forcing gas flow from the gas distribution plate downward toward the wafer center to provide a greater concentration of Chlorine ions over the wafer center, by reducing the effective diameter of the chamber between the gas distribution plate and the wafer to approximately the diameter of the wafer. In a fourth aspect of the invention, etch rate uniformity is enhanced by reducing RF power near the wafer edge periphery, by reducing the RF pedestal to a diameter substantially less than that of the wafer.