Abstract: An image sensor includes a photodiode within a semiconductor substrate and an interconnect structure over the semiconductor substrate. The interconnect structure includes a contact etch stop layer (CESL), a plurality of dielectric layers over the CESL and a plurality of metallization layers in the plurality of dielectric layers. At least one dielectric layer of the plurality of dielectric layers includes a low-k dielectric material. An opening is extended through the plurality of dielectric layers to expose a portion of the CESL above an active region of the photodiode. A cap layer is on sidewalls of the opening. The cap layer includes a dielectric material having a higher moisture resistance than the low-k dielectric material.