In related arts, a Complementary Metal Oxide Semiconductor (CMOS) image sensor provided in a solid-state imaging device includes a plurality of photoelectric conversion devices, a floating diffusion, a transfer transistor, a reset transistor, an amplification transistor, and so on.
The photoelectric conversion device is a device that photoelectrically converts incident light to signal charge in accordance with a light amount and accumulates the signal charge. The transfer transistor is a transistor that transfers the signal charge accumulated in the photoelectric conversion device to the floating diffusion. The amplification transistor is a transistor that amplifies the signal charge transferred to the floating diffusion. The reset transistor is a transistor that resets electrical potential of the floating diffusion to a prescribed electrical potential.
In the mentioned CMOS image sensor, a charge accumulating region for a plurality of the photoelectric conversion devices and channels of the above-described transistors are generally disposed in a same semiconductor layer. Therefore, in the CMOS image sensor, an active region for the transistors is provided inside a well having conductivity type reverse to the charge accumulating region of the photoelectric conversion device and dopant concentration of the well is made higher than a predetermined value, thereby isolating the photoelectric conversion devices from the channels of the transistors.
However, in the case of increasing the dopant concentration in the well in order to improve device isolation characteristics in the solid-state imaging device, modulation degree of the amplification transistor is lowered and a Carrier to Noise Ratio (C/N ratio) of an output signal may be deteriorated, for example.
USPTO Backgrounds
USPTO Backgrounds