Pixel, associated image sensor, and method

A pixel includes a semiconductor substrate, a low-κ dielectric, and a photodiode region in the semiconductor substrate. The semiconductor substrate has a substrate top surface that forms a trench. The trench extends into the semiconductor substrate and has a trench depth relative to a planar region of the substrate top surface surrounding the trench. The low-κ dielectric is in the trench between the trench depth and a low-κ depth with respect to the planar region. The low-κ depth is less than the trench depth. The photodiode region is in the semiconductor substrate and includes (i) a bottom photodiode section beneath the trench and (ii) a top photodiode section adjacent to the trench. The top photodiode section begins at a photodiode depth, with respect to the planar region, that is less than the low-κ depth, and extends toward and adjoining the bottom photodiode section.