Photoelectric conversion device, image pickup system and method of manufacturing photoelectric conversion device

A device, comprising:

• a first semiconductor substrate which includes a photoelectric conversion unit where a plurality of photoelectric conversion elements are arranged, the first semiconductor substrate having a first surface which is a light receiving surface of the first semiconductor substrate and a second surface opposite to the first surface of the first semiconductor substrate;
• a second semiconductor substrate which includes a signal processing unit, the second semiconductor substrate having a first surface where a plurality of transistors which constitutes the signal processing unit and a second surface opposite to the first surface of the second semiconductor substrate;
• and
• a lens array arranged on the second surface of the first semiconductor substrate,
• wherein the first semiconductor substrate is stacked on the second semiconductor substrate, and
• wherein a distance between the first surface of the second semiconductor substrate and the second surface of the second semiconductor substrate is greater than a distance between the first surface of the second semiconductor substrate and a light input surface of the lens array.