Semiconductor device and a method for manufacturing a semiconductor device

A method for manufacturing a semiconductor device, comprising the steps of:

• (a) forming a first nitride semiconductor layer, forming a second nitride semiconductor layer wider in band gap than the first nitride semiconductor layer over the first nitride semiconductor layer, and thereby forming a lamination;
• (b) forming a first silicon nitride film in such a manner as to be in contact with the second nitride semiconductor layer, and forming a second silicon nitride film larger in composition ratio of silicon (Si) than the first silicon nitride film over the first silicon nitride film;
• and
• (c) forming a conductive film over the second nitride semiconductor layer, etching the conductive film until the second silicon nitride film is exposed, and thereby forming a gate electrode.

A semiconductor device comprising:

• a first nitride semiconductor layer formed over a substrate;
• a second nitride semiconductor layer formed over the first nitride semiconductor layer, and wider in band gap than the first nitride semiconductor layer;
• a first insulation film formed over the second nitride semiconductor layer, and having an opening in a first region;
• a gate electrode formed over the second nitride semiconductor layer in the first region;
• and
• a first electrode and a second electrode formed over the second nitride semiconductor layer on the opposite sides of the gate electrode, respectively,
• wherein the first insulation film has a first silicon nitride film formed over the second nitride semiconductor layer, and a second silicon nitride film formed over the first silicon nitride film, and
• wherein the second silicon nitride film is larger in composition ratio of silicon (Si) than the first silicon nitride film.

A semiconductor device comprising:

• a first nitride semiconductor layer formed over a substrate;
• a second nitride semiconductor layer formed over the first nitride semiconductor layer, and wider in band gap than the first nitride semiconductor layer;
• an insulation film formed over the second nitride semiconductor layer;
• a gate electrode;
• and
• a first electrode and a second electrode formed over the second nitride semiconductor layer on the opposite sides of the gate electrode, respectively,
• wherein the insulation film has a first silicon nitride film formed over the second nitride semiconductor layer, a second silicon nitride film formed over the first silicon nitride film, and a third silicon nitride film formed over the second silicon nitride film,
• wherein the second silicon nitride film is larger in composition ratio of silicon (Si) than the first silicon nitride film, and
• wherein the gate electrode is provided at least over the second silicon nitride film, and is provided under the third silicon nitride film.