Manufacturing method of thin film transistor, thin film transistor and display substrate

A manufacturing method of thin film transistor, comprising steps of forming an active layer, which comprise:

• forming a polysilicon pattern layer and a protective pattern layer on a substrate sequentially;
• etching the protective pattern layer with a first etching gas, so as to obtain a protective pattern formed from the protective pattern layer;
• simultaneously etching the protective pattern and the polysilicon pattern layer with a second etching gas by using the protective pattern as a mask, so as to obtain a polysilicon pattern formed from the polysilicon pattern layer and a residual protective pattern formed from the protective pattern, wherein the protective pattern is etched with the second etching gas at a rate no less than a rate at which the polysilicon pattern layer is etched with the second etching gas;
• and
• forming an amorphous silicon pattern, which is in contact with etched sides of the polysilicon pattern, exposes a part of the residual protective pattern, and forms an active layer together with the polysilicon pattern.