Imaging device

An imaging device, comprising:

• a first substrate including a sensor pixel that performs photoelectric conversion;
• a second substrate including a pixel circuit that outputs a pixel signal on a basis of electric charges output from the sensor pixel;
• and
• a third substrate including a processing circuit that performs signal processing on the pixel signal,
• wherein the first substrate, the second substrate, and the third substrate are stacked in this order, and
• wherein, in at least one or more semiconductor layers in which a field-effect transistor of the pixel circuit is provided, a concentration of electrically-conductive type impurities in a region of the first substrate is higher than a concentration of electrically-conductive type impurities in a region of the third substrate,
• wherein the sensor pixel includes a photoelectric conversion element, a transfer transistor electrically coupled to the photoelectric conversion element, and a floating diffusion that temporarily holds the electric charges output from the photoelectric conversion element via the transfer transistor,
• wherein the pixel circuit includes a reset transistor that resets a potential of the floating diffusion to a predetermined potential, an amplification transistor that generates, as the pixel signal, a signal of a voltage corresponding to a level of the electric charges held in the floating diffusion, and a selection transistor that controls an output timing of the pixel signal from the amplification transistor,
• wherein the first substrate includes a first semiconductor substrate including, on a side of a front surface, the photoelectric conversion element, the transfer transistor, and the floating diffusion,
• wherein the second substrate includes a second semiconductor substrate including, on a side of a front surface, the reset transistor, the amplification transistor, and the selection transistor,
• wherein a back surface of the second semiconductor substrate is attached to the front surface of the first semiconductor substrate with an insulating layer interposed therebetween, and
• wherein a first region containing the electrically-conductive type impurities at a higher concentration than another region of the second semiconductor substrate is provided in a region including an interface between the second semiconductor substrate and the insulating layer.