Frontside deep trench isolation (FDTI) structure for CMOS image sensor

A method for forming an image sensor, the method comprising:

• forming a frontside deep trench isolation (FDTI) trench from a frontside of a substrate separating a plurality of pixel regions arranged in rows and columns from a top view;
• filling the FDTI trench followed by a recessing process to form a dummy FDTI structure with a first depth;
• replacing the dummy FDTI structure with a FDTI structure comprising a stack of metal and dielectric layers including a high-k dielectric liner;
• forming a cap layer over the FDTI structure and overlying the plurality of pixel regions;
• forming a plurality of photodiodes of a first doping type from the cap layer and extending in the substrate;
• and
• forming a floating diffusion (FD) node of the first doping type within the cap layer shared by a group of pixel regions within the plurality of pixel regions, wherein the FD node is arranged at a crossroad of the group of pixel regions overlying the FDTI structure.

A method, comprising:

• a substrate having a first pixel region and a second pixel region adjacent to the first pixel region;
• forming a cap layer over a frontside of a substrate;
• forming a first photodiode and a second photodiode extending from the cap layer into the substrate, wherein the first photodiode and the second photodiode are of a first doping type;
• forming a stop layer on the cap layer;
• forming a frontside deep trench isolation (FDTI) structure between the first photodiode and the second photodiode on the stop layer;
• and
• forming a floating diffusion (FD) node of the first doping type within the cap layer and spaced apart from the FDTI structure by the cap layer.