Patent ID: 7666795

Claim:
A method of manufacturing a semiconductor device that includes a Si substrate having a first region and a second region, the method comprising: forming a SiGe layer on the first region of the Si substrate; forming a first Si layer on the SiGe layer; forming a first SiO 2 layer on the first Si layer; forming a Si 3 N 4 layer on the first SiO 2 layer; etching a part of the Si 3 N 4 layer, the SiO 2 layer, and the SiGe layer to form a depressed portion that exposes a side surface of the SiGe layer; forming a second SiO 2 layer over the Si substrate such that the second SiO 2 layer is filled in the depressed portion; forming a first groove that exposes a surface of the substrate by etching a part of the first and second SiO 2 layers and the Si 3 N 4 layer; forming a second groove that reaches a part of the Si 3 N 4 layer by etching another part of the second SiO 2 layer; etching the Si 3 N 4 layer and the first SiO 2 layer inside the first and second grooves to expose a surface of the first Si layer; and etching the SiGe layer to form a cavity by applying an etchant to the first Si layer and the SiGe layer via the first groove.