Image sensor and fabrication method thereof

A method for forming an image sensor, comprising:

• providing a first substrate, the first substrate including a first surface and a second surface that are opposite to each other;
• and
• forming a photoelectric structure in the first substrate, wherein a conductivity type of the photoelectric structure is opposite to a conductivity type of the first substrate, the photoelectric structure includes a second doped region and a plurality of first doped regions, each of the plurality of first doped regions is connected to the second doped region, a distance from the second doped region to the first surface is smaller than a distance from one of the plurality of first doped regions to the first surface, and a size of the plurality of first doped regions in a direction parallel to the first surface of the first substrate is smaller than or equal to a size of the second doped region in the direction parallel to the first surface of the first substrate,
• wherein projection patterns of the plurality of first doped regions on the first surface of the first substrate include a rectangular shape, a square shape, or an annular shape.