Production method of thin film transistor

The invention provides a production method of a thin film transistor. The method comprises the following steps of sequentially depositing a semiconductor layer and a metal layer; coating a photoresist layer on the metal layer; exposing the photoresist layer, patterning the photoresist layer, wherein one part of the photoresist layer is formed into a thin photoresist layer, and the other part is formed into the thick photoresist layer or non-photoresist layer; etching primarily: etching the metal layer and the semiconductor layer to remove the part covered by the non-photoresist layer; graying the photoresist layer, and removing the thin photoresist layer to expose the metal layer positioned under the thin photoresist layer; etching secondarily: etching the metal layer to form a source, a drain and a channel area and expose the semiconductor layer positioned in the channel area; and removing the photoresist layer. According to the production method provided by the invention, one time of utilization of a photom