PURPOSE: To prevent insulation failure from occurring among a gate electrode, a source electrode, and a drain electrode positively by forming a gate insulation film with a silicon nitriding film which has larger silicon atomic weight than stoichiometry ratio and by forming an insulation thin film which consists of a silicon nitriding film which has larger nitrogen atomic weight than the stoichiometric ratio at an interface with a semiconductor layer.

CONSTITUTION: In a thin-film transistor where a gate electrode 12, a gate insulation film 13, a semiconductor layer 14, a source electrode 16, and a drain electrode 17 are laminated, the gate insulation film 13 is formed by silicon nitriding film which has larger silicon atom weight than stoichiometry ratio and an insulation thin film 13a which consists of the silicon nitriding film which las larger nitrogen atomic weight than the stoichiometry ratio is formed at an interface between the gate insulation film 13 and the semiconductor layer 14. For example, the gate insulation film 13 is a silicon nitriding film which is formed by controlling a power density of RF discharge to 60-100mW/cm2 by the plasma CVD device and the insulation thin film 13a at the interface with the semiconductor layer 14 is a silicon nitriding film which is formed by controlling the powder density of RF discharge to 110mW/cm2 or larger by the plasma CVD device.