In recent years, MOS (Metal Oxide Semiconductor) solid-state imaging devices are mounted in mobile cameras, in-vehicle cameras, and monitoring cameras.
These solid-state imaging devices are required to capture images at high resolution, and miniaturization and higher pixel counts are necessary for the solid-state imaging devices. In conventional solid-state imaging devices, the size of a photodiode is also reduced due to a finer pixel. This has caused a problem that the saturation signal level is reduced by decreasing the volume of a photodiode, and sensitivity is reduced by decreasing the aperture ratio.
As a solid-state imaging device for solving such a problem, a layered solid-state imaging device is proposed. The layered solid-state imaging device has a photoelectric conversion film stacked on the top surface of a semiconductor substrate. Furthermore, light is incident from above the layered films. The solid-state imaging device has a structure in which charges generated in the photoelectric conversion film by photoelectric conversion are read out using a Charge Coupled Device (CCD) circuit or a Complementary MOS (CMOS) circuit.
Patent Literature (PTL) 1 discloses a conventional layered solid-state imaging device. FIG. 13 illustrates a circuit diagram of a pixel circuit in the solid-state imaging device described in PTL 1. The pixel circuit shown in FIG. 13 has a charge accumulation region (FD) and a pixel electrode 15a electrically connected to each other, and the voltage varies depending on the incident light intensity. Furthermore, the charge accumulation region is electrically connected to a gate electrode of an amplification transistor 17b. With this, the pixel circuit is capable of amplifying an amount of voltage change in the charge accumulation region to read out the resulting voltage to a signal line 17d. 
In the foregoing layered solid-state imaging device, although the photoelectric conversion film is stacked on the top of a wiring layer used in a reading out circuit and a signal processing circuit, the charges generated by photoelectric conversion are accumulated in the charge accumulation region provided in the semiconductor substrate. This is why the charges generated by photoelectric conversion are transmitted to the charge accumulation region via metal plugs.