Patent ID: 7553713

Claim:
A method of manufacturing a semiconductor substrate, comprising: forming a first semiconductor layer on a part of the semiconductor substrate; forming a second semiconductor layer on the first semiconductor layer, the second semiconductor layer having an etching rate to a first etching solution lower than an etching rate to the first etching solution of the first semiconductor layer; forming an insulating film on the semiconductor substrate so as to cover the first semiconductor layer and the second semiconductor layer; forming an aperture in the insulating film, so that a part of an edge of the first semiconductor layer and a part of an edge of the second semiconductor layer are exposed through the aperture; forming a cavity below the second semiconductor layer by etching the first semiconductor layer through the aperture by using the first etching solution; and forming a first oxide film to fill up the cavity; wherein the forming of the cavity including: removing a first portion of the first semiconductor layer by using a second etching solution such that a second portion of the first semiconductor layer remains; and removing the second portion of the first semiconductor layer by using the first etching solution, a first difference between an etching rate of the first semiconductor layer to the first etching solution and an etching rate of the second semiconductor layer to the first etching solution being larger than a second difference between an etching rate of the first semiconductor layer to the second etching solution and an etching rate of the second semiconductor layer to the second etching solution.