Thin film transistor and manufacturing method thereof

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

• forming an amorphous semiconductor film over a substrate having an insulating surface;
• forming a crystalline semiconductor film by crystallizing the amorphous semiconductor film;
• forming an island-shaped semiconductor film by etching the crystalline semiconductor film;
• forming a gate insulating film over the island-shaped semiconductor film;
• forming a conductive film over the gate insulating film;
• forming a gate electrode by etching the conductive film;
• slimming the gate electrode by oxidizing a surface of the gate electrode using high-density plasma;
• and
• removing an oxide film formed over the surface of the gate electrode.

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

• forming an amorphous semiconductor film over a substrate having an insulating surface;
• forming a crystalline semiconductor film by crystallizing the amorphous semiconductor film;
• forming an island-shaped semiconductor film by etching the crystalline semiconductor film;
• forming a gate insulating film over the island-shaped semiconductor film;
• forming a conductive film over the gate insulating film;
• forming a gate electrode by etching the conductive film;
• slimming the gate electrode by oxidizing a surface of the gate electrode using high-density plasma;
• doping the island-shaped semiconductor film with first impurity ion using the gate electrode as a mask;
• forming a sidewall on a side surface of the gate electrode;
• and
• doping the island-shaped semiconductor film with second impurity ion to have a higher concentration of that of the first impurity ion, using the gate electrode and the sidewall as a mask.

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

• forming an amorphous semiconductor film over a substrate having an insulating surface;
• forming a crystalline semiconductor film by crystallizing the amorphous semiconductor film;
• forming an island-shaped semiconductor film by etching the crystalline semiconductor film;
• forming a gate insulating film over the island-shaped semiconductor film;
• forming a conductive film over the gate insulating film;
• forming a gate electrode by etching the conductive film;
• slimming the gate electrode by oxidizing a surface of the gate electrode using high-density plasma;
• removing an oxide film formed over the surface of the gate electrode;
• doping the island-shaped semiconductor film with first impurity ion using the gate electrode as a mask;
• forming a sidewall on a side surface of the gate electrode;
• and
• doping the island-shaped semiconductor film with second impurity ion to have a higher concentration of that of the first impurity ion, using the gate electrode and the sidewall as a mask.