Power semiconductor device structure for integrated circuit and method of fabrication thereof

A trench-gate semiconductor device comprising:

• a semiconductor substrate having a first major surface;
• a trench extending from the first major surface (3) into the substrate;
• first and second impurity doped regions of a first conductivity type at respective first and second opposing sides of the trench adjacent the first major surface;
• a body region of a second conductivity type, opposite to the first conductivity type, formed only below the first impurity doped region on the first side of the trench;
• a drift region of the first conductivity type, below the body region and the second impurity doped region, the trench terminating in the drift region;
• a conductive gate insulated from the body region by a gate insulator, and
• a conductive field plate in the trench, the field plate extending into the trench parallel to the conductive gate to depth greater than or equal to the depth of the conductive gate, wherein the field plate is insulated from the drift region in the trench by a field plate insulating layer, and wherein the thickness of the field plate insulating layer is substantially greater than the thickness of the gate insulator.