Method for fabricating thin film transistor

The present invention relates to a method for fabricating thin film transistor, more particularly, to a method for fabricating thin film transistor which not only manufactures a polycrystalline silicon layer having large grain size and containing a trace of residual metal catalyst by heat treating thereby crystallizing the metal catalyst layer after forming an amorphous silicon layer on a substrate, forming a capping layer formed of nitride film having 1.78 to 1.90 of the refraction index when crystallizing the amorphous silicon layer and forming a metal catalyst layer on the capping layer, but also controls characteristics of the polycrystalline silicon layer by controlling the refraction index of the capping layer.