Mesa type semiconductor device and manufacturing method thereof

Abstract

This invention is directed to solving problems with a mesa type semiconductor device, which are deterioration in a withstand voltage and occurrence of a leakage current caused by reduced thickness of a second insulation film on an inner wall of a mesa groove corresponding to a PN junction, and offers a mesa type semiconductor device of high withstand voltage and high reliability and its manufacturing method. After the mesa groove is formed by dry-etching, wet-etching with an etching solution including hydrofluoric acid and nitric acid is further applied to a sidewall of the mesa groove to form an overhang made of the first insulation film above an upper portion of the mesa groove. The overhang serves as a barrier to prevent the second insulation film formed in the mesa groove and on the first insulation film around the mesa groove beyond an area of the overhang from flowing toward a bottom of the mesa groove due to an increased fluidity resulting from a subsequent thermal treatment. As a result, the inner wall of the mesa groove corresponding to the PN junction is covered with the second insulation film thick enough to secure a desired withstand voltage and to reduce a leakage current.