Photo detector and optically interconnected LSI

An optically interconnected LSI comprising:

• a semiconductor substrate which has a main surface;
• a transistor unit configured to be integrally formed on the main surface of the semiconductor substrate;
• a multilayer-interconnection structure unit which is provided on the transistor unit;
• an electrically conductive thin film which is provided on the multilayer-interconnection structure unit and has an upper surface, a lower surface, a coupling periodic structure formed on the upper surface, and an opening penetrating the upper surface and the lower surface, the opening being formed of a slit having a length longer than half a wavelength of a surface plasmon converted from incident light in a direction that intersects at a right angle with a polarization direction of the incident light and a width narrower than half the wavelength of the surface plasmon in a direction that is parallel to the polarization direction;
• an electrically conductive pillar having upper and lower surfaces and configured to penetrate the upper and lower surfaces of the multilayer-interconnection structure unit and has a waveguide opening penetrating the upper and lower surfaces of the electrically conductive pillar, an end of the waveguide opening communicating with the opening of the electrically conductive thin film;
• and
• a semiconductor light-receiving unit which is provided on the surface of the semiconductor substrate and located at the other end of the waveguide opening of the electrically conductive pillar.