Method of etching sacrificial layer

A method of etching a sacrificial layer, adapted for an integrated circuit process and comprising:

• providing a substrate formed with a sacrificial layer, and defined with a first region and a second region, wherein the sacrificial layer disposed in both the first region and the second region;
• forming a hard mask covering the first region while exposing the second region;
• performing a first etching process on the sacrificial layer on the substrate by using the hard mask as an etch mask to thin the sacrificial layer while forming a byproduct film overlying the thinned sacrificial layer;
• performing a second etching process on the byproduct film to remove a portion of the byproduct film for exposing a portion of the thinned sacrificial layer, while another portion of the byproduct film disposed on sides of the thinned sacrificial layer being remained;
• and
• performing a third etching process on the thinned sacrificial layer having the remained byproduct film disposed on the sides thereof, to remove the portion of the thinned sacrificial layer exposed in the second etching process.