JPS571254A - Semiconductor device and its manufacture - Google Patents

Abstract

PURPOSE:To form a perfectly protective film and to prevent contamination and deterioration of withstand voltage of a semiconductor device by a method wherein the top face of convex parts consisted of polycrystalline Si layers having concave and convex faces with gently-sloping circumferences are provided on the surface of a substrate utilizing the difference of etching speed between monocrystalline Si and polycrystalline Si. CONSTITUTION:A P<+> type layer 2 is provided in the N<-> type Si substrate 1, P type layers 3 are buried therein selectively, an N<-> type layer 41, an N<+> type layer 42 are formed epitaxially in continuation, and concentration and thickness thereof are selected as to obtain the necessitated withstand voltage between gate and cathode. An N<+> type polycrystalline Si layer 43 is accumulated thereon. Selective etching is performed after heat treatment to form a gate electrode lead out part 31, and the form of the main face on the cathode side is regulated as to form the concave and convex shape. At this time, because of existence of the polycrystalline Si layer 43 and rapid etching speed of polycrystalline Si, the circumferences 7 of the convex parts become as gently-sloping. When they are coated with SiO2 films 8 and resist masks, because uniform coatings can be formed, generation of unnecessitated etching and invasion of a harmful impurity can be avoided at those parts. Accordingly deterioration of withstand voltage between the gate and the cathode can be prevented.