| 摘要 |
In a semiconductor device, a first trench having a uniformly inclined surface at a predetermined angle is formed downward from the surface of a semiconductor substrate. A second trench is formed vertically downward from the first trench. These trenches are filled with an insulating film to form a trench element isolation structure. The inclined surface of the first trench can disperse stepwise the electric field generated at an element isolation end and can relax concentration of electrical charges. The second trench vertically extending downward can reliably isolate elements. The semiconductor device has a trench element isolation structure made of the insulating film filling the trenches. The outer edge of a portion projecting from the semiconductor substrate is covered with a thermal oxide film formed by heat-treating a polysilicon film. The structure is more resistant to etching, cleaning, and the like. The semiconductor substrate can be satisfactorily separated from the gate electrode. Concentration of the electric field at the element isolation end can be relaxed to improve the electrical characteristics of a transistor.
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