Abstract: A semiconductor device 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 when 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 (21) and then impurities are injected to the bottom surface of the source trench (21). When the impurities are heated and diffused, the buried P+-type diffusion region (14) is formed with a width almost identical to the width of the opening of the source trench (21) or smaller than the width (B) of the opening of the source trench (21). Thus, even when irregularities are generated in the manufacturing step and the buried diffusion region (14) becomes larger than is necessary, it is possible to prevent contact of the buried diffusion region (14) with the gate trench (20).

Abstract: A technique is provided which makes it possible to reduce the area of a power MOSFET. A power MOSFET 1 according to the invention is a trench type in which a source region 27 is exposed on both of a substrate top surface 51 and an inner circumferential surface 52 of a trench 18. Since this makes it possible to provide contact between the source region 27 and a source electrode film 29 not only on the substrate top surface 51 but also on the inner circumferential surface 52 of the trench 18, source contact is provided with a sufficiently low resistance only on the substrate top surface, and the area of the device can be made smaller than that in the related art in which the source region 27 has been formed in a larger area.

Abstract: A technique is provided which makes it possible to reduce the area of a power MOSFET. A power MOSFET 1 according to the invention is a trench type in which a source region 27 is exposed on both of a substrate top surface 51 and an inner circumferential surface 52 of a trench 18. Since this makes it possible to provide contact between the source region 27 and a source electrode film 29 not only on the substrate top surface 51 but also on the inner circumferential surface 52 of the trench 18, source contact is provided with a sufficiently low resistance only on the substrate top surface, and the area of the device can be made smaller than that in the related art in which the source region 27 has been formed in a larger area.

Abstract: A technique for reducing an on-resistance of a transistor is provided. A power MOSFET of the present invention has a semiconductor material which is disposed under a polysilicon gate and composed of polysilicon into which impurities are doped at low concentration. Therefore, a depletion layer is expanded to the inside of the semiconductor material under the polysilicon gate. Since the electric field strengths are uniform from the surface of a drain layer to a depth of the bottom surface of the semiconductor material and a high electric field is not generated at one site, the avalanche breakdown voltage of the transistor is increased. Therefore, the concentration of impurities in drain layer can be made higher than that in a conventional transistor and thereby the on-resistance of the transistor 1 can be reduced.

Abstract: A technique for reducing an on-resistance of a transistor is provided. A power MOSFET of the present invention has a semiconductor material which is disposed under a polysilicon gate and composed of polysilicon into which impurities are doped at low concentration. Therefore, a depletion layer is expanded to the inside of the semiconductor material under the polysilicon gate. Since the electric field strengths are uniform from the surface of a drain layer to a depth of the bottom surface of the semiconductor material and a high electric field is not generated at one site, the avalanche breakdown voltage of the transistor is increased. Therefore, the concentration of impurities in drain layer can be made higher than that in a conventional transistor and thereby the on-resistance of the transistor 1 can be reduced.

Abstract: A technique for reducing an on-resistance of a transistor is provided. A power MOSFET of the present invention has a semiconductor material which is disposed under a polysilicon gate and composed of polysilicon into which impurities are doped at low concentration. Therefore, a depletion layer is expanded to the inside of the semiconductor material under the polysilicon gate. Since the electric field strengths are uniform from the surface of a drain layer to a depth of the bottom surface of the semiconductor material and a high electric field is not generated at one site, the avalanche breakdown voltage of the transistor is increased. Therefore, the concentration of impurities in drain layer can be made higher than that in a conventional transistor and thereby the on-resistance of the transistor 1 can be reduced.

Abstract: The capacitance between the gate electrode film and the drain layer of semiconductor device is reduced while keeping the resistance low, with the withstand voltage of the gate insulating film also being maintained at a sufficient level. A trench 10 is formed with the bottom of the trench at a comparatively shallow position in an N-epitaxial layer 18. The thickness of a bottom surface part 16 of a gate electrode film 11 is formed so as to be thicker than other parts of the gate electrode film 11. Also, when a P type body layer 19 is formed, an interface between the P type body layer 19 and an N-epitaxial layer 18 is located at a deeper position than a bottom end of the gate electrode film 11.

Abstract: A technique for reducing an on-resistance of a transistor is provided. A power MOSFET of the present invention has a semiconductor material which is disposed under a polysilicon gate and composed of polysilicon into which impurities are doped at low concentration. Therefore, a depletion layer is expanded to the inside of the semiconductor material under the polysilicon gate. Since the electric field strengths are uniform from the surface of a drain layer to a depth of the bottom surface of the semiconductor material and a high electric field is not generated at one site, the avalanche breakdown voltage of the transistor is increased. Therefore, the concentration of impurities in drain layer can be made higher than that in a conventional transistor and thereby the on-resistance of the transistor 1 can be reduced.