Thin film transistor and method of making same

A method for forming a thin film transistor comprising:

• providing a substrate;
• forming a gate electrode on the substrate;
• forming an electrically insulating layer on the substrate to cover the gate electrode therein;
• forming a semiconductor layer on the electrically insulating layer;
• forming an etch stop layer on the semiconductor layer;
• forming a photoresist layer on the etch stop layer;
• processing the photoresist layer by photolithography using a mask to have the photoresist layer become a first photoresist pattern which has a configuration in cross section of a trapezoid defining at least two recesses in a top thereof;
• etching two lateral end portions of the etch stop layer which are not covered by the first photoresist pattern, whereby the etch stop layer becomes an etch stop pattern;
• deforming the first photoresist pattern to cause the first photoresist pattern to move downwardly to reach the semiconductor layer, whereby the first photoresist pattern becomes a second photoresist pattern;
• etching two lateral end portions of the semiconductor layer which are not covered by the second photoresist pattern, whereby the semiconductor layer becomes a channel layer for the thin film transistor;
• ashing the second photoresist pattern to cause the second photoresist pattern to become a third photoresist pattern having the at least two recesses, the etch stop pattern being exposed to atmosphere via the at least two recesses in the third photoresist pattern;
• etching the etch stop pattern via the at least two recesses in the third photoresist pattern to cause the etch stop pattern to define at least a first through hole and at least a second through hole therein;
• removing the third photoresist pattern;
• and
• forming a source electrode electrically coupling with a lateral end of the channel layer and a drain electrode electrically coupling with an opposite lateral end of the channel layer.