Patent attributes
An example semiconductor device is capable of preventing a buried diffusion region formed near the bottom surface of a source trench from diffusing to the extent that it contacts a gate trench in the vicinity of that buried diffusion region even if the accuracy of the photographic step of trench formation is not so high. A side wall is formed on the circumferential side of the source trench and then impurities are injected to the bottom surface of the source trench. When the impurities are heated and diffused, the buried P+-type diffusion region is formed with a width almost identical to the width of the opening of the source trench or smaller than the width of the opening of the source trench. Thus, even when irregularities are generated in the manufacturing step and the buried diffusion region becomes larger than is necessary, it is possible to prevent contact of the buried diffusion region with the gate trench.