Patent ID: 8580695

Claim:
A method of fabricating a semiconductor device, comprising: forming a substantially “U” shaped recess in a Si substrate; treating the “U” shaped recess with a surfactant, wherein an amount of surfactant adsorbed on sidewalls of the “U” shaped recess is larger than an amount adsorbed on a bottom of the “U” shaped recess; forming an oxide on the bottom of the “U” shaped recess, wherein the surfactant adsorbed on the sidewalls of the “U” shaped recess prevents the oxide from being formed on the sidewalls; removing the surfactant on the sidewalls of the “U” shaped recess using a first cleaning agent; performing orientation selective wet etching on the sidewalls of the “U” shaped recess with an etchant using the oxide as an etching stop layer, so as to form a “Σ” shaped recess; and removing the oxide on the bottom of the “U” shaped recess using a second cleaning agent.