Patent ID: 8628676

Claim:
A plasma etching method in which plasma is generated from a processing gas and a silicon substrate is etched to form a tapering etching structure having a wide top opening width and a narrow bottom width in the silicon substrate, the method comprising: a first step in which a first processing gas comprising a fluorine-containing gas and N 2 gas but absent O 2 gas is used to generate plasma, wherein plasma generated by the fluorine-containing gas etches a first portion of the tapering etching structure into the silicon substrate while plasma generated by the N 2 gas forms a first etch-resistant layer on the silicon substrate; and a second step, subsequent to the first step, in which a second processing gas comprising a fluorine-containing gas and an oxygen-containing gas is used to generate plasma, wherein plasma generated by the fluorine-containing gas etches a second portion of the tapering etching structure into the silicon substrate while plasma generated by the oxygen-containing gas forms a second etch-resistant layer on the silicon substrate.