Pixel with dual-PD layout

A method for forming an image sensor, comprising:

• forming a first semiconductor structure, which comprises a pair of photodetectors in a first substrate;
• forming a second semiconductor structure, which comprises a plurality of pixel transistors on a second substrate;
• bonding the first semiconductor structure and the second semiconductor structure together, such that the pair of photodetectors and the plurality of pixel transistors form a pixel;
• forming a trench isolation structure extending completely through the first substrate and completely separating the pair of photodetectors from each other;
• and
• forming a color filter shared by and overlying both of the pair of photodetectors on an opposite side of the first substrate as the second semiconductor structure.

A method for forming an image sensor, comprising:

• forming a first integrated circuit (IC) die comprising a plurality of photodetectors and a plurality of transfer transistors, wherein the plurality of photodetectors and source/drain regions of the plurality of transfer transistors are in a first substrate;
• forming a second IC die comprising a plurality of pixel transistors on a second substrate;
• bonding the second IC die to the first substrate to form a pixel that comprises the plurality of photodetectors, the plurality of transfer transistors, and the plurality of pixel transistors;
• forming a third IC die comprising a plurality of logic transistors;
• bonding the third IC die to the second IC die on an opposite side of the second IC die as the first IC die;
• and
• forming a trench isolation structure extending through the first substrate after the bonding of the third IC die, wherein the trench isolation structure separates the source/drain regions of the plurality of transfer transistors from each other.