A DRAM having integration capacitors coupled to dummy memory cells of a folded bitline arrangement is disclosed. The read voltage is stepped and the as-read sum codes are compared to the expected sum codes to determine the Vt range that provides matching sum codes. Each of the auxiliary light receiving regions is positioned in a direction orthogonal to a drawing direction of the division line so as to be adjacent to the main light receiving region. The complete sterilization process is carried out while the chamber remains sealed and without removal of any component of the sterilization atmosphere.