Patent ID: 8492280

Claim:
A method of forming a first feature and a second feature in a substrate, the method comprising: providing a stack of layers comprising a substrate layer, a buried oxide (BOX) layer on the substrate layer, a semiconductor-on-insulator (SOI) layer on the BOX layer, a nitride layer on the SOI layer, and a silicon oxide layer on the nitride layer; forming a first opening in the silicon oxide layer, the nitride layer, the SOI layer, and the oxide layer; forming a second opening in the silicon oxide layer, the nitride layer, the SOI layer, and the oxide layer, wherein the second opening has a smaller cross-sectional area than the first opening; etching the first opening to form a first feature and the second opening to form a second feature with a first etching gas; etching the first feature and the second feature with a second etching gas, wherein the first feature is deeper than the second feature and the second etching gas comprises the first etching gas and a halogenated silicon compound.