Concave reflector for complementary metal oxide semiconductor image sensor (cis)

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

• forming a photodetector within a substrate;
• forming an inter-layer dielectric (ILD) structure over the substrate;
• depositing a first etch stop layer (ESL) over the ILD structure;
• performing a first etch selectively into the first ESL and the ILD structure to form a first recess overlying the photodetector, wherein the ILD structure defines a bottom surface of the first recess that has edges closer to the substrate than a center of the bottom surface;
• forming a reflector filling the first recess;
• depositing an inter-metal dielectric (IMD) layer over the first ESL and the reflector;
• and
• forming a wire in the IMD layer and the first ESL.

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

• forming a photodetector within a substrate;
• forming a dielectric structure over the substrate;
• forming a mask over the dielectric structure, wherein the mask defines an opening overlying the photodetector;
• performing an etch into the dielectric structure with the mask in place to form a reflector recess extending into the dielectric structure, wherein the etch has a higher etch rate at a periphery of the opening than that at a center of the opening;
• and
• forming a reflector filling and conforming to the reflector recess.