Semiconductor device and method for manufacturing the same

1. A method for manufacturing semiconductor device, the method comprising the steps of:

sequentially forming a gate oxide film, a polysilicon film and a first nitride film on a semiconductor substrate;

etching the first nitride film, polysilicon film, gate oxide film and a predetermined depth of the semiconductor substrate to form a trench;

forming a device isolation film by filling up the trench to define an active region;

removing the first nitride film;

etching a predetermined thickness of the device isolation film to form a recess;

forming a second nitride film filling the recess;

forming a stacked structure of a barrier metal film, a metal layer and a third nitride film on the second nitride film and the polysilicon film;

etching the stacked structure and the second nitride film via a photoetching process using a gate line mask to form a gate electrode comprising a stacked structure of second nitride film pattern, a barrier metal film pattern, a metal layer pattern and a third nitride film pattern;

forming an insulating film spacer on a sidewall of the gate electrode;

etching the polysilicon film using the third nitride film pattern and the insulating film spacer as a mask to form a polysilicon film pattern; and

forming an oxide film on a sidewall of the polysilicon film pattern.

2. The method according to claim 1 , wherein the step of forming a second nitride film comprises:

forming a nitride layer having a predetermined thickness on the entire surface of the polysilicon film and within the recess;

forming a sacrificial oxide film on the entire nitride layer filling the recess;

performing planarization to expose the nitride layer; and

removing the sacrificial oxide film to form the second nitride film.

3. The method according to claim 1 , wherein the first nitride film has a thickness ranging from 10 to 70 nm.

4. The method according to claim 1 , wherein the depth of the recess ranges from 20 to 200 nm.

5. The method according to claim 1 , wherein the second nitride film has a thickness ranging from 10 to 90 nm.

6. The method according to claim 1 , wherein the barrier metal film comprises a metal selected from the group consisting of WN, TiN and TiSiN, and the metal layer comprises a metal selected from the group consisting of tungsten, titanium silicide, tungsten silicide and cobalt silicide.