Mesa type semiconductor device and manufacturing method thereof

Abstract

Problems with a conventional mesa type semiconductor device, which are deterioration in a withstand voltage and occurrence of a leakage current caused by reduced thickness of an insulation film on an inner wall of a mesa groove corresponding to a PN junction, are solved using an inexpensive material, and a mesa type semiconductor device of high withstand voltage and high reliability is offered together with its manufacturing method. A stable protection film made of a thermal oxide film is formed on the inner wall of the mesa groove in the mesa type semiconductor device to cover and protect the PN junction, and an insulation film having negative electric charges is formed to fill a space in the mesa groove covered with the thermal oxide film so that an electron accumulation layer is not easily formed at an interface between an Ntype semiconductor layer and the thermal oxide film. With the structure described above, an influence of the positive electric charges in the thermal oxide film is weakened and an extension of a depletion layer into the Ntype semiconductor layer at the interface with the thermal oxide film is secured.