Shield or ring surrounding semiconductor workpiece in plasma chamber

Abstract

A ring or collar surrounding a semiconductor workpiece in a plasma chamber. According to one aspect, the ring has an elevated collar portion having an inner surface oriented at an obtuse angle to the plane of the workpiece, this angle preferably being 135°. This angular orientation causes ions bombarding the inner surface of the elevated collar to scatter in a direction more parallel to the plane of the workpiece, thereby reducing erosion of any dielectric shield at the perimeter of the workpiece, and ameliorating spatial non-uniformity in the plasma process due to any excess ion density near such perimeter. In a second aspect, the workpiece is surrounded by a dielectric shield, and the shield is covered by a non-dielectric ring which protects the dielectric shield from reaction with, or erosion by, the process gases. In a third aspect, the dielectric shield is thin enough to couple substantial power from the cathode to the plasma, thereby improving spatial uniformity of the plasma process near the perimeter of the workpiece. In a fourth aspect, azimuthal non-uniformities in process performance can be ameliorated by corresponding azimuthal variations in the dimensions of the elevated collar and/or the dielectric shield surrounding the workpiece.