Patent ID: 7112505

Claim:
A method of selectively etching a HSG layer, comprising the steps of: providing a semiconductor substrate having a trench therein; forming a buried oxide layer on the upper sidewall of the trench, wherein the buried oxide layer is adjacent to a top surface of the semiconductor substrate; conformally forming a HSG layer on the sidewall and bottom of the trench; conformally forming a doping dielectric layer on the HSG layer; filling a mask layer into the trench, and recessing the mask layer to a predetermined depth; removing the doping dielectric layer not covered by the mask layer to expose a portion of the HSG layer; ion doping the exposed HSG layer to form a plasma doping layer on the upper sidewall and top of the trench; and isotropically etching the plasma doping layer on the upper sidewall and top of the trench, with an etching selectivity higher than 1:20 for plasma doping layer to silicon substrate.