Method for forming backside illumination CMOS image sensor

A method for forming a backside illumination CMOS image sensor, comprising:

• providing a first substrate, wherein the first substrate has a first surface and a second surface opposite to each other;
• forming a photoelectric epitaxial layer on the second surface, wherein the photoelectric epitaxial layer has a third surface and a fourth surface opposite to each other, and the second surface is adjacent to the third surface, wherein the photoelectric epitaxial layer comprises a groove extending from the fourth surface to the third surface, and the photoelectric epitaxial layer comprises a plurality of first doped areas and a plurality of second doped areas surrounding the plurality of first doped areas respectively;
• forming a device layer after forming the groove and the photoelectric epitaxial layer;
• forming an isolation layer in the groove;
• providing a second substrate and a third substrate;
• disposing the fourth surface to face the second substrate and bonding the photoelectric epitaxial layer and the second substrate after forming the groove and the photoelectric epitaxial layer and before forming the device layer;
• disposing the third surface to face the third substrate and bonding the photoelectric epitaxial layer and the third substrate after forming the device layer;
• removing the second substrate to expose the fourth surface after bonding the photoelectric epitaxial layer and the third substrate;
• and
• forming a filter layer on the fourth surface and the isolation layer and a plurality of lenses on a surface of the filter layer after exposing the fourth surface.