Method of making an image sensor with sidewall protection

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

• forming a photodiode in a substrate;
• forming an interconnect structure over the substrate, wherein the interconnect structure comprises a low-k dielectric material;
• etching the interconnect structure to define an opening over the photodiode;
• depositing a cap layer along sidewalls and a bottom surface of the opening, wherein the cap layer comprises a dielectric material having a higher moisture resistance than the low-k dielectric material;
• and
• removing the cap layer from the bottom surface of the opening.

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

• forming a photodiode in a substrate;
• depositing a contact etch stop layer (CESL) over the substrate, wherein the CESL is over the photodiode;
• forming an interconnect structure over the CESL, wherein the interconnect structure comprises a first dielectric material;
• defining an opening, using etching, over the photodiode, wherein the opening exposes a portion of the CESL;
• depositing a cap layer along sidewalls and a bottom surface of the opening, wherein the cap layer comprises a second dielectric material having a higher moisture resistance than the first dielectric material;
• and
• forming a gate structure over the photodiode, wherein the gate structure comprises a gate dielectric and a gate electrode, the CESL is over the gate structure, and defining the opening comprises etching into the gate structure.