Semiconductor device for display device using thin film transistors and process of manufacturing the same

A method of manufacturing a thin film transistor, said transistor comprising a single polycrystalline layer, said layer having a selected field effect mobility, said method comprising the steps of:

• forming a first polycrystalline silicon film on an insulation substrate;
• forming an amorphous silicon film on said first polycrystalline silicon film;
• forming a second polycrystalline silicon film from said amorphous silicon film, by subjecting said amorphous silicon film to one of a solid phase growth and a recrystallization process, whereby said single polycrystalline layer comprises both said first polycrystalline silicon film and said second polycrystalline silicon film;
• controlling said steps of forming said first and second polycrystalline silicon films to obtain said selected field effect mobility of said single polycrystalline layer by varying a ratio of thickness of said first polycrystalline silicon film to thickness of said second polycrystalline silicon film;
• forming a gate insulation layer on said second polycrystalline silicon film;
• forming a gate electrode on said gate insulation layer;
• and
• forming source and drain regions at positions adjacent to said gate electrode in said first and second polycrystalline silicon films.

A method of manufacturing an integral driver type display device in which a pixel portion and a pixel driving circuit are provided on an insulation substrate, said method comprising the steps of:

• forming a first polycrystalline silicon film on the insulation substrate in such a manner that the thickness of the silicon film in the area associated with the pixel portion is thicker than the thickness of the silicon film in the area associated with the pixel driving circuit;
• forming an amorphous silicon film on said first polycrystalline silicon film;
• and
• forming a second polycrystalline silicon film from said amorphous silicon film, by subjecting the amorphous silicon to one of a solid phase growth and a recrystallization process.