Patent ID: 8563413

Claim:
A method for fabricating a semiconductor device, comprising: providing a substrate having an active region defined by a device isolation layer; forming a trench in the active region and a trench in the device isolation layer by etching the active region and the device isolation layer; performing a nitriding process to form an oxidation protecting layer over the trench in the device isolation layer, and to form a gate insulation layer over the trench in the active region; forming a buried gate filling a portion of each trench, in each trench; and forming an interlayer insulation layer filling a remainder of each trench, over the buried gate, wherein the performing of a nitriding process comprises: forming a silicon nitride layer over the trench in the active region while a silicon oxynitride layer is formed over the trench in the device isolation layer as the oxidation protecting layer: removing the silicon nitride layer to expose a surface of the trench in the active region: and forming the gate insulation layer over the trench in the active region by performing an oxidizing process to the trench in the active region.