Back-side deep trench isolation (bdti) structure for pinned photodiode image sensor

A CMOS image sensor, comprising:

• a substrate having a front-side and a back-side opposite to the front-side;
• a photodiode arranged within the substrate;
• a back-side deep trench isolation (BDTI) structure extending from the back-side of the substrate to positions within the substrate on opposing sides of the photodiode;
• and
• a back-end-of-the-line (BEOL) metallization stack arranged on the front-side of the substrate and comprising a plurality of metal interconnect layers arranged within an inter-level dielectric layer;
• wherein the BDTI structure comprises a doped layer with a first doping type and a dielectric fill layer, the doped layer lining a sidewall surface of a deep trench and the dielectric fill layer filling a remaining space of the deep trench.

A method of forming an image sensor, comprising:

• forming doping layers corresponding to photodiodes of a plurality of pixel regions from a front-side of a substrate;
• forming a doped isolation layer from the front-side of the substrate by implanting a dopant species into the substrate through a plurality of implanting processes, the doped isolation layer comprising a vertical portion between adjacent pixel regions;
• rotating the substrate and etching from a back-side of the substrate to form a deep trench between adjacent pixel regions and extending into the substrate, wherein the back-side of the substrate opposes the front-side of the substrate;
• and
• filling the deep trench with a doped layer and a dielectric fill layer a dielectric layer to form a back-side deep trench isolation (BDTI) structure that are disposed between the adjacent pixel regions and separate photodiodes of the adjacent pixel regions.