Structure for preventing field concentration in semiconductor device and method of forming the same

In a semiconductor device comprising a first conductivity type semiconductor substrate, a second conductivity type first semiconductor region formed on said semiconductor substrate which is isolated from said semiconductor substrate through p-n junction isolation, and a conductive layer extending above said first semiconductor region across an end portion of said first semiconductor region, a structure for preventing field concentration caused in said end portion of said first semiconductor region, existing under said conductive layer, through influence exerted by an electric field from said conductive layer, comprising:

• an insulating film formed on said end portion of said first semiconductor region between said first semiconductor region and said conductive layer;
• at least one conductive plate each having a first and second end portion and being formed in said insulating film in a manner that said at least one conductor plate is fully surrounded by said insulating film so as to be in a fully electrically floating state;
• and
• at least two first conductivity type first semiconductor floating diffusion regions formed in a surface of said end portion of said first semiconductor region to be alternately arranged with said conductive plate so that said first end portion of said at least one conductive plate overlaps with one of said at least two first conductivity type first semiconductor floating diffusion regions and said second end portion of said at least one conductive plate overlaps with another one of said at least two first conductivity type first semiconductor floating diffusion regions through said insulating film.