CMOS image sensor including superlattice to enhance infrared light absorption

A CMOS image sensor comprising:

• a semiconductor substrate having a first conductivity type;
• a plurality of laterally adjacent infrared (IR) photodiode structures on the substrate and each comprising
• a superlattice on the semiconductor substrate comprising a plurality of stacked groups of layers, 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, the superlattice having the first conductivity type;
• and
• a semiconductor layer on the superlattice,
• a retrograde well extending downward into the semiconductor layer from a surface thereof and having a second conductivity type,
• a first well around a periphery of the retrograde well having the first conductivity type, and
• a second well above the retrograde well having the first conductivity type;
• a respective IR filter overlying each of the IR photodiode structures;
• and
• a respective microlens overlying each of the IR filters.

A CMOS image sensor comprising:

• a semiconductor substrate having a first conductivity type;
• a plurality of laterally adjacent infrared (IR) photodiode structures on the substrate and each comprising
• a superlattice on the semiconductor substrate comprising a plurality of stacked groups of layers, each group of layers comprising a plurality of stacked base silicon monolayers defining a base silicon portion, and at least one oxygen monolayer constrained within a crystal lattice of adjacent base silicon portions, the superlattice having the first conductivity type,
• a semiconductor layer on the superlattice,
• a retrograde well extending downward into the semiconductor layer from a surface thereof and having a second conductivity type,
• a first well around a periphery of the retrograde well having the first conductivity type, and
• a second well above the retrograde well having the first conductivity type.