Methods for manufacturing thin film transistor and display device

A method for manufacturing a thin film transistor, comprising the steps of:

• forming a gate insulating layer over a gate electrode layer;
• forming a semiconductor layer over the gate insulating layer;
• forming a patterned semiconductor layer by etching the semiconductor layer, the patterned semiconductor layer overlapping at least a part of the gate electrode layer;
• forming a conductive layer over the gate insulating layer and the patterned semiconductor layer;
• etching the conductive layer to form source and drain electrode layers by using a resist mask over the conductive layer;
• removing the resist mask after forming the source and drain electrode layers, wherein a back channel portion of the patterned semiconductor layer is exposed between the source and drain electrode layers;
• and
• performing a plasma treatment on a surface of the back channel portion to remove contamination materials from the surface of the back channel portion, after removing the resist mask.

A method for manufacturing a thin film transistor, comprising the steps of:

• forming a gate insulating layer over a gate electrode layer;
• forming a semiconductor layer over the gate insulating layer;
• forming a conductive layer over the semiconductor layer;
• etching portions of the semiconductor layer and the conductive layer by using a first resist mask having a depression portion to form a patterned semiconductor layer overlapping at least a part of the gate electrode layer wherein the first resist mask is simultaneously etched so that the depression portion reaches the conductive layer, thereby forming a second resist mask;
• etching the conductive layer to form source and drain electrode layers by using the second resist mask over the conductive layer;
• removing the second resist mask, wherein a back channel portion of the patterned semiconductor layer is exposed between the source and drain electrode layers;
• and
• performing a plasma treatment on a surface of the back channel portion to remove contamination materials from the surface of the back channel portion, after removing the second resist mask.