Patent ID: 7858476

Claim:
A method for fabricating a semiconductor device, the method comprising: forming a hard mask pattern over a substrate; forming a first recess in the substrate and a passivation layer on sidewalls of the first recess using the hard mask pattern as an etch barrier, the first recess having a vertical profile; performing a second recess etching to form a second recess, the second recess etching being a slightly isotropical etching process and arranged to etch a bottom portion of the first recess using the passivation layer as an etch barrier, wherein a width of the second recess is greater than that of the first recess; and after forming the second recess, performing an isotropical etching to extend sidewalls of the second recess using the passivation layer as an etch barrier, wherein forming of the first recess and the passivation layer comprises using a plasma mixture including chlorine (Cl 2 ) and nitrogen (N 2 ) gases as a main etching gas and a hydrogen (H 2 ) gas as an additional etching gas, wherein the second recess etching comprises using a gas mixture including HBr and Cl 2 gases and SF 6 and O 2 gases, and wherein the isotropical etching comprises using a gas mixture including HBr, Cl 2 and O 2 gases and a NF x or CF x gas.