Patent ID: 7294538

Claim:
A method of manufacturing a thin film transistor using a laser irradiation device including a projection lens, the method comprising: depositing an amorphous silicon thin film on a substrate; irradiating a laser beam from the laser irradiation device onto the thin film through an exposure mask having a slit pattern to form a polysilicon layer after preheating the projection lens wherein the preheating is performed without irradiating a laser beam from the irradiation device onto the thin film; patterning the polysilicon layer to form a semiconductor layer; depositing a first insulating layer on the semiconductor layer, forming a gate electrode on the first insulating layer; implanting impurities into the semiconductor layer to form source and drain regions; depositing a second insulating layer on the gate electrode; forming contact holes exposing the source and the drain regions in the first or the second insulating layers; and forming source and drain electrodes respectively connected to the source and the drain regions through the contact holes.