Patent ID: 7629214

Claim:
A method of manufacturing a semiconductor device, comprising the steps of: forming a backgate diffusion layer on a semiconductor layer, including forming a first diffusion layer, having a peak of an impurity concentration located at a deeper portion of the semiconductor layer, and forming at least one second diffusion layer, having a peak of an impurity concentration located closer to the surface of the semiconductor layer than the peak of the impurity concentration of the first diffusion layer, wherein the first and second diffusion layers are overlapped and wherein the second diffusion layer extends essentially completely within the first diffusion layer in direction of depth of the semiconductor layer; forming a gate oxide film and a gate electrode on the semiconductor layer; and forming a source diffusion layer and a drain diffusion layer by implanting impurity ions into the backgate diffusion layer and thereafter diffusing the impurity ions, wherein the drain diffusion layer is formed such that the drain diffusion layer has a slope relative to a surface of the semiconductor layer and an angle is formed between a tangent line to the slope and the surface of the semiconductor layer, which angle gets smaller toward the surface of the semiconductor layer.