Method of forming a thin film transistor

1. A method of forming a thin film transistor, comprising:

providing a substrate;

forming a gate electrode on the substrate;

forming a microcrystal material layer on the gate electrode;

performing a plasma treatment to transfer the microcrystal material layer into a buffer layer;

forming a gate insulating layer on the buffer layer;

forming an active channel layer on the gate insulating layer;

forming a source and a drain on the active channel layer; and

forming a source electrode and a drain electrode contacting the source and the drain respectively.

2. The method as claimed in claim 1 , wherein the buffer layer comprises silicon nitride.

3. The method as claimed in claim 2 , wherein the microcrystal material layer comprises microsilicon.

4. The method as claimed in claim 3 , wherein a processing gas used in the plasma treatment comprises nitrogen.

5. The method as claimed in claim 1 , wherein the buffer layer comprises silicon oxynitride.

6. The method as claimed in claim 5 , wherein the microcrystal material layer comprises silicon.

7. The method as claimed in claim 6 , wherein a processing gas used in the plasma treatment comprises N 2 O.

8. The method as claimed in claim 1 , wherein the microcrystal material layer comprises a silicon layer deposited by an enhanced plasma chemical vapor deposition (PECVD) process using a processing gas comprising SiH 4 /H 2 with a ratio of less than 20 percent by volume.

9. The method as claimed in claim 1 , wherein the steps of forming the microcrystal material layer and performing the plasma treatment are repeated until the buffer layer reaches a determined thickness.

10. The method as claimed in claim 1 , wherein the buffer layer has a thickness of about 50 to 200 Å.

11. The method as claimed in claim 1 , wherein the gate electrode comprises Cu, Ag, Al, Mo, Cr, W, Ta, their alloys, or a stacked layer thereof.

12. A method of forming a thin film transistor, comprising:

providing a substrate;

forming a gate electrode on the substrate;

performing a deposition procedure and a plasma treatment procedure of a microcrystal material layer on the gate electrode under a vacuum system, the deposition procedure and the plasma treatment procedure being repeated to form a buffer layer covering the gate electrode;

depositing a gate insulating layer, a semiconductor layer and a first conductive type semiconductor layer on the buffer layer without breaking the vacuum system;

forming a metal layer on the first conductive type semiconductor layer; and

defining the metal layer and the first conductive type semiconductor layer to form a source electrode, a drain electrode, a source and a drain.

13. The method as claimed in claim 12 , wherein the buffer layer comprises silicon nitride.

14. The method as claimed in claim 13 , wherein the microcrystal material layer comprises silicon layer and a processing gas used in the plasma treatment procedure comprises nitrogen.

15. The method as claimed in claim 12 , wherein the buffer layer comprises a silicon oxynitride layer.

16. The method as claimed in claim 15 , wherein the microcrystal material layer comprises silicon layer and a processing gas used in the plasma treatment procedure comprises N 2 O.

17. The method as claimed in claim 12 , wherein the microcrystal material layer comprises silicon layer deposited by enhanced plasma chemical vapor deposition (PECVD) process using a processing gas comprising SiH 4 /H 2 with a ratio of less than 20 percent by volume.

18. The method as claimed in claim 12 , wherein the buffer layer has a thickness of about 50 to 200 Å.

19. The method as claimed in claim 12 , wherein the first conductive type semiconductor layer comprises an n+ type semiconductor layer.