Method for fabricating semiconductor device with buried gates

1. A method for fabricating a semiconductor device, comprising:

forming a trench by etching a semiconductor substrate;

forming a gate insulation layer over a surface of the trench;

forming a gate conductive layer over the gate insulation layer;

performing a first recess process by etching the gate conductive layer;

forming a protection pattern over the gate insulation layer; and

performing a second recess process by etching the gate conductive layer.

2. The method of claim 1 , wherein the protection pattern comprises a nitride layer.

3. The method of claim 1 , wherein the forming of the protection pattern comprises:

depositing a nitride layer over the gate conductive layer; and

etching the nitride layer in such a manner that the nitride layer remains at the top corner of the trench and is at least substantially removed at the bottom of the trench.

4. The method of claim 3 , wherein the etching of the nitride layer is performed using a mixed gas which includes tetrafluoromethane (CF 4 ), fluoroform (CHF 3 ), oxygen (O 2 ) and argon (Ar) with a bias power ranging from approximately 200 V to approximately 300 V.

5. The method of claim 3 , wherein the nitride layer is formed in a thickness ranging from approximately 20 Å to approximately 30 Å.

6. The method of claim 1 , wherein a recess amount of the gate conductive layer during the first recess process is controlled to be within a range of approximately 100 Å to approximately 150 Å and a recess amount of the gate conductive layer during the second recess process is controlled to be within a range of approximately 500 Å to approximately 700 Å.

7. The method of claim 1 , wherein the forming the trench by etching the semiconductor substrate uses a hard mask pattern as an etch barrier.

8. The method of claim 7 , further comprising:

planarizing the gate conductive layer to expose the hard mask pattern before the first etching process.

9. The method of claim 8 , wherein the stripping includes a wet etch process.

10. The method of claim 1 , further comprising:

stripping the protection pattern and the hard mask pattern after the second etching process.

11. The method of claim 1 , wherein the gate conductive layer includes a titanium nitride layer and a tungsten layer.

12. The method of claim 1 , wherein the first recess process is wet etch process.

13. The method of claim 1 , wherein the second recess process is dry etch process.

14. The method of claim 1 , further comprising:

performing a post-cleaning after the second recess process, wherein the post-cleaning process is performed using a mixed solution prepared by mixing sulfuric acid (H 2 SO 4 ) and hydrogen peroxide (H 2 O 2 ) at a mixing ratio ranging from approximately 40:1 to approximately 60:1 for approximately 1 minute to approximately 5 minutes.

15. The method of claim 14 , wherein an additional cleaning process is performed using a buffered oxide etchant (BOE) after the post-cleaning process performed using the mixed solution of sulfuric acid (H 2 SO 4 ) and hydrogen peroxide (H 2 O 2 ).

16. A method for fabricating a semiconductor device, comprising:

forming a trench by etching a semiconductor substrate using a hard mask pattern as an etch barrier;

forming a gate insulation layer on a surface of the trench;

forming a gate conductive layer gap-filling the trench over the gate insulation layer;

planarizing the gate conductive layer to expose a surface of the hard mask pattern;

performing a first recess process by etching the gate conductive layer;

forming a protection pattern for protecting the gate insulation layer at a top corner of the trench;

performing a second recess process by etching the gate conductive layer to form a buried gate; and

performing a post-cleaning onto the buried gate.

17. The method of claim 16 , wherein the etching of the first recess process includes a wet etch process.

18. The method of claim 16 , wherein the etching of the second recess process includes a dry etch process.

19. The method of claim 16 , wherein the forming of the protection pattern comprises:

depositing a nitride layer over a structure including the recessed gate conductive layer resulting from performing the first recess process; and

etching the nitride layer in such a manner that the nitride layer remains at the top corner of the trench and is at least substantially removed at the bottom of the trench.

20. The method of claim 16 , further comprising:

stripping the protection pattern and the hard mask pattern after the post-cleaning process, wherein the stripping of the protection pattern includes performing a wet etch process.