Method for fabricating semiconductor device

A method for fabricating a semiconductor device, comprising:

• etching a predetermined portion of a substrate to form a first recess having a roundly projected bottom middle portion and bottom edge portions tapered to have a micro-trench profile, the bottom edge portions being deeper than the bottom middle portion;
• etching the substrate beneath the first recess to form a second recess, the second recess being rounded and being wider than the first recess;
• rounding top corners of the first recess;
• forming a gate insulation layer over the substrate with the first recess and the second recess formed therein;
• and
• forming a gate pattern having a first portion filled into the first and second recesses and a second portion projected above the substrate over the gate insulation layer;
• wherein forming the first recess includes performing a plasma etching with a mixture gas including a chlorine-based gas and an inert gas.