of 20 kev and an injecting amount of 1 0 u00d7 10 15 cm 2 a heat treatment is performed e g under the nitride atmosphere at 900 u00b0 c for 15 minutes to activate the injected ions 3 at the time of reducing the resistances of the polysilicon films 32 and 33 impurities to be doped may be other proper materials than phosphorus such as arsenic antimony phosphorus oxychloride etc 4 the silicon nitride film 31 may be replaced with a silicon oxide film and the side wall spacer 35 may be formed by a silicon nitride film not a silicon oxide film 5 the silicon nitride film 31 may be replaced with a proper insulating layer and the side wall spacer 35 may be formed of a proper material whose etching ratio differs from that of this insulating layer 6 the interlayer insulating film 14 is not limited to a silicon oxide film and may be any insulating film such as a silicon nitride film alumina or silicate glass when a different material from a silicon oxide film is used for the interlayer insulating film 14 an mos metal oxide semiconductor transistor and an mos capacitor become an mis metal insulator semiconductor transistor and an mis capacitor in a broader sense 7 the polysilicon film 33 may be replaced with an hsg hemispherical grain polysilicon film in this case the surface of the polysilicon film 33 becomes rough further increasing the surface area of the dielectric film 17 so that this invention becomes more effective the details on the method of forming an hsg polysilicon film are given in a report from micro electronics laboratory in nec corporation kasai sakao et al shingaku technology vol 90 sdm90 202 p 47 1990 8 a.