a semiconductor substrate having a number of pixels, said semiconductor substrate comprising a first region including a charge accumulation region of a photodiode, a floating diffusion, and a first isolation region formed in the semiconductor substrate, and a second region including transistors and a second isolation region formed in the semiconductor substrate, each having a gate electrode and source/drain regions;

a first silicon oxide film formed on said semiconductor substrate, covering a surface of said charge accumulation region in said first region and patterned as side wall spacers remaining on side walls of the gate electrode of at least some transistors in said second region;

a silicon nitride film formed on said first silicon oxide film, directly contacting the source/drain regions outside said side wall spacers in said second region and having an opening at least in an area above said charge accumulation region in said first region;

a first conductive plug penetrating through both said silicon oxide film and said silicon nitride film, and contacting with the floating diffusion and not contacting with the first isolation region; and

a second conductive plug penetrating through said silicon nitride film and contacting with the source/drain regions of said at least some transistors in said second region and the second isolation region.