Methods for manufacturing thin film transistor and display device

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

• forming a back channel portion in the thin film transistor by conducting etching using a resist mask;
• removing the resist mask;
• and
• etching a superficial part of the back channel portion using a nitrogen gas or a tetrafluoromethane gas.

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

• forming a back channel portion in the thin film transistor by conducting etching using a resist mask;
• removing the resist mask using a chemical solution containing a hydrophilic group including sulfur;
• and
• etching a superficial part of the back channel portion using a nitrogen gas or a tetrafluoromethane gas so that a concentration of sulfur which exists in the back channel portion is made less than and equal to a detection limit by secondary ion mass spectrometry.

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

• forming a gate insulating layer, a semiconductor layer, and an impurity semiconductor layer over a gate electrode layer;
• forming a first resist mask selectively over the impurity semiconductor layer;
• etching the semiconductor layer and the impurity semiconductor layer so that an island-shaped semiconductor layer at least part of which overlaps with the gate electrode layer is formed;
• removing the first resist mask;
• forming a conductive layer over the gate insulating layer and the island-shaped semiconductor layer;
• forming a second resist mask selectively over the conductive layer;
• etching the conductive layer so that source and drain electrodes are formed;
• etching the impurity semiconductor layer of the island-shaped semiconductor layer with the second resist mask left so that part of the semiconductor layer is exposed and a back channel portion is formed;
• removing the second resist mask using a chemical solution containing a hydrophilic group including sulfur;
• and
• etching a superficial part of the back channel portion with the source and drain electrodes used as masks so that a concentration of sulfur which exists in the back channel portion is made less than and equal to a detection limit by secondary ion mass spectrometry.

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

• forming a gate insulating layer, a semiconductor layer, and an impurity semiconductor layer over a gate electrode layer;
• forming a first resist mask selectively over the impurity semiconductor layer;
• etching the semiconductor layer and the impurity semiconductor layer so that an island-shaped semiconductor layer at least part of which overlaps with the gate electrode layer is formed;
• removing the first resist mask;
• forming a conductive layer over the gate insulating layer and the island-shaped semiconductor layer;
• forming a second resist mask selectively over the conductive layer;
• etching the conductive layer so that source and drain electrodes are formed;
• removing the second resist mask using a chemical solution containing a hydrophilic group including sulfur;
• etching the impurity semiconductor layer of the island-shaped semiconductor layer with the source and drain electrodes used as masks so that part of the semiconductor layer is exposed and a back channel portion is formed;
• and
• etching a superficial part of the back channel portion so that a concentration of sulfur which exists in the back channel portion is made less than and equal to a detection limit by secondary ion mass spectrometry.

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

• forming a gate insulating layer, a semiconductor layer, an impurity semiconductor layer, and a conductive layer over a gate electrode layer;
• forming a first resist mask having a depression portion selectively over the conductive layer;
• etching the semiconductor layer, the impurity semiconductor layer, and the conductive layer so that an island-shaped semiconductor layer is formed and a conductive layer is formed over the semiconductor layer and so that the depression portion of the first resist mask is made to reach the conductive layer, whereby a second resist mask is formed;
• etching the conductive layer so that source and drain electrodes are formed;
• etching the impurity semiconductor layer of the island-shaped semiconductor layer so that part of the semiconductor layer is exposed and a back channel portion is formed;
• removing the second resist mask using a chemical solution containing a hydrophilic group including sulfur;
• and
• etching a superficial part of the back channel portion with the source and drain electrodes used as masks so that a concentration of sulfur which exists in the back channel portion is made less than and equal to a detection limit by secondary ion mass spectrometry.

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

• forming a gate insulating layer, a semiconductor layer, an impurity semiconductor layer, and a conductive layer over a gate electrode layer;
• forming a first resist mask having a depression portion selectively over the conductive layer;
• etching the semiconductor layer, the impurity semiconductor layer, and the conductive layer so that an island-shaped semiconductor layer is formed and a conductive layer is formed over the semiconductor layer and so that the depression portion of the first resist mask is made to reach the conductive layer, whereby a second resist mask is formed;
• etching the conductive layer so that source and drain electrodes are formed;
• removing the second resist mask using a chemical solution containing a hydrophilic group including sulfur;
• etching the impurity semiconductor layer of the island-shaped semiconductor layer so that part of the semiconductor layer is exposed and a back channel portion is formed;
• and
• etching a superficial part of the back channel portion with the source and drain electrodes used as masks so that a concentration of sulfur which exists in the back channel portion is made less than and equal to a detection limit by secondary ion mass spectrometry.