Thin film transistor and method of fabricating the same

1. A thin film transistor comprising:

a substrate;

a semiconductor layer containing a polysilicon material crystallized by an super grain silicon (SGS) crystallization method and disposed over the substrate, wherein the polysilicon material is defined as having a contact angle with a liquid droplet of about 40 to about 80 degrees when the liquid droplet is placed onto a flat surface made of the polysilicon material; and

a gate insulating layer, a gate electrode, an interlayer insulating layer, and source and drain electrode, which are disposed over the semiconductor layer.

2. The thin film transistor according to claim 1 , wherein the liquid droplet has a diameter between about 2 mm and about 5 mm.

3. The thin film transistor according to claim 1 , wherein the liquid droplet comprises a water droplet.

4. The thin film transistor according to claim 1 , wherein the polysilicon material contains a metal catalyst, the metal catalyst having a concentration of about 10 13 atoms/cm 2 or less.

5. A method of making a thin film transistor, the method comprising:

forming a semiconductor layer over a substrate, the semiconductor layer comprising amorphous silicon;

forming a capping layer over the semiconductor layer;

forming a metal catalyst layer over the capping layer, the metal catalyst layer comprising a metal catalyst;

annealing the substrate, the semiconductor layer, the capping layer, and the metal catalyst layer, such that at least a portion of the metal catalyst diffuses into the semiconductor layer, and such that the amorphous silicon is crystallized into polysilicon;

removing the metal catalyst layer; and

removing the capping layer from over the semiconductor layer, to an extent that, when a liquid droplet is placed over the semiconductor layer, a contact angle between the semiconductor layer and the liquid droplet is from about 40 degrees to about 80 degrees.

6. The method of claim 5 , further comprising measuring the contact angle after removing the capping layer.

7. The method of claim 5 , wherein the capping layer is single-layered.

8. The method of claim 5 , wherein the capping layer comprises multiple layers.

9. The method of claim 5 , wherein the capping layer comprises one or more materials selected from the group consisting of silicon oxide and silicon nitride.

10. The method of claim 9 , wherein the polysilicon is more hydrophobic than the capping layer.

11. The method of claim 9 , wherein, after removing the catalyst layer and before removing the capping layer, the capping layer has a contact angle of about 40 degrees or less when a liquid droplet is placed on the capping layer.

12. The method of claim 5 , further comprising patterning the semiconductor layer after removing the capping layer.

13. The method of claim 5 , wherein the liquid droplet has a diameter between about 2 mm and about 5 mm.

14. The method of claim 5 , wherein the liquid droplet comprises a water droplet.

15. The method of claim 5 , wherein the contact angle is an acute angle formed between a baseline of the liquid droplet and a tangential line at a droplet boundary.

16. A method of making a display device comprising a thin film transistor (TFT), the method comprising:

providing an intermediate device comprising a substrate, a polysilicon layer over the substrate, a capping layer over the polysilicon layer;

removing the capping layer from over the polysilicon layer; and

determining whether the capping layer has been substantially completely removed from over the polysilicon layer, wherein the determining comprises: placing a liquid droplet over the polysilicon layer; and measuring a contact angle between a baseline of the liquid droplet and a tangential line at a droplet boundary.

17. The method of claim 16 , further comprising, after measuring the contact angle, patterning the semiconductor layer if the measured contact angle is from about 40 degrees to about 80 degrees.