Method for manufacturing display device

A method for manufacturing a display device, comprising:

• forming an amorphous semiconductor layer over an insulated surface;
• adding a metal element to the amorphous semiconductor layer and crystallizing the amorphous semiconductor layer by heating to form a crystalline semiconductor layer;
• forming a channel protection layer over the crystalline semiconductor layer;
• forming a semiconductor layer having one conductivity type over the crystalline semiconductor layer and the channel protection layer;
• heating the crystalline semiconductor layer and the semiconductor layer having one conductivity type;
• patterning the semiconductor layer having one conductivity type to form a source region and a drain region;
• discharging a composition containing a conductive material on the source region and the drain region to selectively form a source electrode layer and a drain electrode layer;
• forming a gate insulating layer over the crystalline semiconductor layer, the channel protection layer, the source electrode layer and the drain electrode layer;
• and
• forming a gate electrode layer over the gate insulating layer.

A method for manufacturing a display device, comprising:

• forming a first semiconductor layer over an insulated surface;
• adding a metal element to the first semiconductor layer and heating the first semiconductor layer;
• forming a second semiconductor layer including a first impurity element in contact with the first semiconductor layer;
• heating the first semiconductor layer and the second semiconductor layer including the first impurity element;
• removing the second semiconductor layer including the first impurity element;
• adding a second impurity element to the first semiconductor layer to form a source region and a drain region;
• discharging a composition containing a conductive material on the source region and the drain region to selectively form a source electrode layer and a drain electrode layer;
• forming a gate insulating layer over the crystalline semiconductor layer, the source electrode layer and the drain electrode layer;
• and
• forming a gate electrode layer over the gate insulating layer.

A method for manufacturing a display device, comprising:

• forming a first semiconductor layer over an insulated surface;
• adding a metal element to the first semiconductor layer and heating the first semiconductor layer;
• forming a second semiconductor layer including a first impurity element in contact with the first semiconductor layer;
• heating the first semiconductor layer and the second semiconductor layer including the first impurity element;
• removing the second semiconductor layer including the first impurity element;
• forming a channel protection layer over a channel formation region of the first semiconductor layer;
• adding a second impurity element to the first semiconductor layer to form a source region and a drain region;
• discharging a composition containing a conductive material on the source region and the drain region to selectively form a source electrode layer and a drain electrode layer;
• forming a gate insulating layer over the crystalline semiconductor layer, the channel protection layer, the source electrode layer and the drain electrode layer;
• and
• forming a gate electrode layer over the gate insulating layer.