Image sensor with sidewall protection and method of making same

An image sensor comprising:

• a photodiode within a semiconductor substrate;
• a gate stack over the photodiode, the gate stack comprising a gate dielectric and a gate electrode over the gate dielectric;
• an interconnect structure over the semiconductor substrate, the interconnect structure comprising:
• a contact etch stop layer (CESL);
• and
• a plurality of dielectric layers over the CESL, wherein at least one dielectric layer of the plurality of dielectric layers comprises a low dielectric constant (low-k) dielectric material;
• an opening extending through the plurality of dielectric layers, the CESL and the gate electrode, the opening exposing a portion of the gate dielectric above an active region of the photodiode;
• and
• a cap layer present at least on sidewalls of the opening, wherein the cap layer comprises a dielectric material having a higher moisture resistance than the low-k dielectric material.

An image sensor comprising:

• a photodiode within a semiconductor substrate;
• an interconnect structure over the semiconductor substrate, the interconnect structure comprising:
• a contact etch stop layer (CESL),
• a plurality of dielectric layers over the CESL, wherein at least one dielectric layer of the plurality of dielectric layers comprises a low dielectric constant (low-k) dielectric material;
• and
• a plurality of metallization layers in the plurality of dielectric layers;
• an opening extending through at least a portion of the interconnect structure;
• and
• a cap layer on sidewalls of the opening, wherein the cap layer comprises a dielectric material having a higher moisture resistance than the low-k dielectric material.