Method for making cmos image sensor including photodiodes with overlying superlattices to reduce crosstalk

Abstract

A method for making a CMOS image sensor may include forming a plurality of laterally adjacent photodiodes on a semiconductor substrate having a first conductivity types by forming a retrograde well extending downward into the substrate from a surface thereof and having a second conductivity type, forming a first well around a periphery of the retrograde well also having the second conductivity type, and forming a second well within the retrograde well having the first conductivity type. Furthermore, first and second superlattices may be respectively formed overlying each of the first and second wells, with each of the first and second superlattices comprising a plurality of stacked groups of layers, and each group of layers comprising a plurality of stacked base semiconductor monolayers defining a base semiconductor portion and at least one non-semiconductor monolayer constrained within a crystal lattice of adjacent base semiconductor portions.