Patent ID: 7851300

Claim:
A method comprising: forming a second conductive type first epitaxial layer and a second conductive type second epitaxial layer over a first conductive type semiconductor substrate; and then forming a first conductive type body region over the second conductive type second epitaxial layer; and then injecting first conductive type impurities in the first conductive type body region in order that a bottom area thereof has a circular cross-section; and then forming a plurality of trenches spaced apart in the first conductive body region; and then forming a gate oxide layer in a respective one of the trenches; and then forming a gate in a respective one of the trenches; and then forming second conductive type emitter regions in the first conductive type body region; and then forming a contact hole at the upper surface of the first conductive type body region between adjacent ones of the second conductive type emitter regions, wherein the first conductive type body region between the bottom area of the contact hole and the second conductive type second epitaxial layer is formed to maintain a predetermined thickness.