Thin film transistor, display substrate, methods for manufacturing the same and display device

A method for manufacturing a thin film transistor, comprising:

• forming a light-shielding metal pattern and a source-drain metal layer pattern on a base substrate;
• forming a buffer layer covering the light-shielding metal pattern and the source-drain metal layer pattern, and patterning the buffer layer to form a first via-hole exposing a part of the light-shielding metal pattern and a second via-hole exposing a part of the source-drain metal layer pattern;
• forming a semiconductor layer pattern on the buffer layer, wherein the semiconductor layer pattern comprises a source electrode region, a drain electrode region, and an active layer between the source electrode region and the drain electrode region, an orthographic projection of the light-shielding metal pattern on the base substrate completely covers an orthographic projection of the active layer on the base substrate and at least covers a part of an orthographic projection of the source electrode region on the base substrate and a part of an orthographic projection of the drain electrode region on the base substrate, the source electrode region is electrically connected with the light-shielding metal pattern via the first via-hole, and the drain electrode region is electrically connected with the source-drain metal layer pattern via the second via-hole;
• and
• forming a gate insulation layer pattern and a gate electrode on the semiconductor layer pattern, wherein an orthographic projection of the gate insulation layer pattern on the base substrate coincides with an orthographic projection of the gate electrode on the base substrate.