1. Technical Field
The present disclosure relates to a laser apparatus and a manufacturing method of a thin film transistor using the same, and more particularly to a laser apparatus used to make an amorphous silicon layer uniform during a crystallization process and a manufacturing method of a thin film transistor substrate using the same.
2. Discussion of the Related Art
A flat panel display device is widely used for a display device. The flat panel display device comprises, for example, a liquid crystal display or an organic light emitting diode display.
The liquid crystal display and the organic light emitting diode display show images by different mechanisms, but both include thin film transistors.
The thin film transistor comprises, for example, a channel area, a gate electrode, a source electrode, and a drain electrode. The channel area may be formed by amorphous silicon. The amorphous silicon has low electrical properties and reliability due to its low mobility.
A polysilicon thin film transistor of which the channel area is formed by polysilicon having mobility of about 20 cm3/Vsec to about 150 cm3/Vsec has been developed. Since the polysilicon thin film transistor has higher mobility than a thin film transistor comprising the channel area formed by an amorphous silicon, chip in glass, which means forming a driving circuit within a substrate, can be performed without difficulty by the polysilicon thin film transistor.
Processes for forming polysilicon layers include an evaporating process evaporating the polysilicon on the substrate at high temperature, a high temperature crystallization process depositing the amorphous silicon and crystallizing the amorphous silicon at about 600° C., and a heat treating process depositing the amorphous silicon and treating by laser.
A conventional process using the laser comprises a sequential lateral solidification (SLS) method and an excimer laser annealing (ELA) method. In the SLS method, grains of the polysilicon grow parallel with the substrate. In the ELA method, grains of the polysilicon grow perpendicular to the substrate.
The ELA process crystallizes the amorphous silicon by scanning the amorphous silicon layer with a strip-shaped laser beam. While the size of the substrate becomes larger, the length of the laser beam is limited. Accordingly, a double scan method scanning the laser beam twice to one substrate has been employed. However, the double scan method generates an overlapping region where the laser beam is overly irradiated, thereby causing the polysilicon layer to be inhomogeneous.