An RIE method and apparatus provides uniform and selective etching through silicon nitride material of a supplied workpiece such as a silicon wafer having silicon oxide adjacent to the SiN. A plasma- maintaining gas that includes N.sub.2 having an inflow rate of at least 10 sccm is used to provide etch-depth uniformity across the workpiece. The plasma-maintaining gas further includes HBr and one or both of NF. sub.3 and SF.sub.6.
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