Patent ID: 8203152

Claim:
A nitride semiconductor device comprising: a nitride semiconductor layer, an insulating layer, a separation preventing layer, and a metal layer, wherein the nitride semiconductor layer is formed on a first surface of a substrate, the nitride semiconductor layer has a projecting portion and a recessed portion, the projecting portion has an upper surface and side surfaces, the recessed portion has lower surfaces adjacent to and extending from the side surfaces of the projecting portion, and the nitride semiconductor layer has the insulating layer and the metal layer thereon; wherein the insulating layer is formed directly on the lower surfaces of the recessed portion and the side surfaces of the projecting portion, and the insulating layer is configured to expose the upper surface of the projecting portion; wherein the separation preventing layer is formed directly on the insulating layer above the lower surfaces of the recessed portion, the separation preventing layer is formed directly between the insulating layer and the metal layer, the separation preventing layer is configured to expose the upper surface of the projecting portion, the separation preventing layer is not in contact with sidewalls of the nitride semiconductor layer, and the separation preventing layer includes, as a main component, at least one metal oxide selected from the group consisting of oxides of tungsten, molybdenum, chromium, titanium, nickel, hafnium, zinc, indium, and yttrium; wherein the metal layer is formed directly on the separation preventing layer and on the upper surface of the projecting portion, a portion of the metal layer is formed directly on the separation preventing layer on the insulating layer above the lower surfaces of the recessed portion, the portion of the metal layer has a contact surface in which the portion of the metal layer is in contact with an upper surface of the separation preventing layer, and the contact surface has, as a main component, at least one metal selected from the group consisting of molybdenum and; wherein a thickness of the insulating layer is greater than that of the separation preventing layer; and wherein the insulating layer and the separation preventing layer are formed of different materials.