Patent ID: 6921723

Claim:
A method of etching a substrate structure comprising: providing a substrate structure comprising: a silicon wafer, a dielectric layer over said silicon wafer, a doped polycrystalline silicon layer over said dielectric layer, and a patterned mask structure over said substrate structure, said patterned mask structure having apertures formed therein; and etching said dosed polycrystalline silicon layer through said apertures by a plasma etching process, wherein said plasma etching process is conducted at a pressure ranging from about 2 to 20 mT in the presence of a plasma source gas that comprises SF 6 M and one or more fluorine-containing gases selected from the group consisting of C 3 F 6 , C 4 F 8 , C 5 F 8 , CH 2 F 2 , C 4 F 6 , wherein a ratio of said SF 6 to said one or more fluorine-containing gases ranges from 0.67 to 1.5.