Patent ID: 7405461

Claim:
A semiconductor device comprising: an element isolating region; a semiconductor substrate; a first layer including impurities formed on the semiconductor substrate; a first trench formed in the element isolating region, the first trench including an inner surface having a rounded corner; a first thermal oxidation film formed on the inner surface of the first trench; a first embedment layer formed in the first trench; a second trench formed in the first trench and extending into the first embedment layer, the first thermal oxidation film, the first layer, and the semiconductor substrate, the second trench including an inner surface having a rounded corner and being deeper than the first trench; a second thermal oxidation film, which is different from the first thermal oxidation film, formed on the inner surface of the second trench, and the second thermal oxidation film covering a surface of the first layer in the second trench and being thinner than the first thermal oxidation film; a second embedment film filling the second trench; an oxidation film formed in the second trench between the second thermal oxidation film and the second embedment film; an element region isolated on the semiconductor substrate by the first trench and the second trench; and a semiconductor element formed on the element region.