Patent ID: 7829472

Claim:
A method of forming at least an opening using a tri-layer structure, comprising: providing a substrate; forming a tri-layer structure on the substrate, the tri-layer structure comprising a bottom photoresist layer on the substrate, a silicon-containing layer on the bottom photoresist layer, and a top photoresist layer on the silicon-containing layer; patterning the top photoresist layer; performing a first etching process on the silicon-containing layer by utilizing the patterned top photoresist layer as an etching mask to pattern the silicon-containing layer and to partially expose the bottom photoresist layer; performing a second etching process on the partially exposed bottom photoresist layer by utilizing the patterned silicon-containing layer as an etching mask to remove parts of the bottom photoresist layer, the second etching process using an oxygen gas and at least one non-carbon-containing halogen-containing gas; performing a third etching process on the partially exposed bottom photoresist layer remaining on the substrate by utilizing the patterned silicon-containing layer as an etching mask to partially expose the substrate, the third etching process using a halogen-containing gas; and etching the partially exposed substrate by utilizing the patterned bottom photoresist layer as an etching mask to form at least an opening in the substrate.