Multiple deep trench isolation (mdti) structure for cmos image sensor

A CMOS image sensor, comprising:

• a substrate having a front-side and a back-side opposite to the front-side;
• a plurality of pixel regions disposed on the substrate and respectively comprising a transfer gate arranged on the front-side of the substrate and a photodiode arranged at one side of the transfer gate and configured to convert radiation that enters the substrate from the back-side into an electrical signal;
• a boundary deep trench isolation (BDTI) structure disposed between adjacent pixel regions, extending from the back-side of the substrate to a first depth within the substrate, and surrounding the photodiode;
• and
• a multiple deep trench isolation (MDTI) structure disposed within the individual pixel region, extending from the back-side of the substrate to a second depth within the substrate, and overlying the photodiode;
• wherein the MDTI structure comprises a first oxide layer lining sidewalls of a MDTI trench, a high-k dielectric layer disposed on the first oxide layer, and a second oxide layer filling remaining spaces of the MDTI trench.

A CMOS image sensor, comprising:

• a transfer gate disposed over a front-side of a substrate;
• a plurality of photodiodes within a plurality of pixel regions and disposed within the substrate at one side of the transfer gate;
• a multiple deep trench isolation (MDTI) structure disposed overlying the photodiodes at a back-side of the substrate;
• a boundary deep trench isolation (BDTI) structure disposed between adjacent pixel regions and surrounding the photodiodes.