Patent ID: 6855633

Claim:
A method for fabricating a semiconductor device using a substrate having a substrate insulator layer and a semiconductor layer provided on the substrate insulator layer and formed with an active layer of a semiconductor element, the method comprising the steps of: (a) forming a mask for forming an active region on a surface portion of the semiconductor layer; (b) forming a dummy side wall over side surfaces of the mask for forming the active region; (c) etching the semiconductor layer by using the mask for forming active region and the dummy sidewall as a mask, thereby forming a trench that reaches the substrate insulator layer; (d) after the step (c), filling the trench with an insulating film for isolation; (e) after the step (d), removing the dummy sidewall to expose an upper-surface edge portion of the semiconductor layer; and (f) after the step (e), oxidizing the upper-surface edge portion of the semiconductor layer.