Photodetector with reduced dark current sensitivity and methods of forming the same

A method of forming a photodetector, comprising:

• forming a patterned hard mask layer on a front side of a first semiconductor substrate;
• performing a first etching process to form recesses in exposed portions of the front side of the first semiconductor substrate, using a first etchant comprising a first halogen species;
• performing a second etching process using a second etchant comprising a second halogen species, such that the second halogen species forms barrier layers in the first semiconductor substrate, surrounding the recesses;
• growing detection regions comprising single-crystal germanium (Ge) in the recesses using an epitaxial growth process,
• forming a passivation layer on the detection regions;
• forming a first interconnect structure over the front surface of the first semiconductor substrate;
• forming a second interconnect structure on a second semiconductor substrate, the second semiconductor substrate comprising photodetector sensing circuits;
• and
• bonding the first interconnect structure and the second interconnect structure, wherein,
• the first etching process comprises implanting the first halogen species in the first semiconductor substrate to a first depth,
• the second etching process comprises implanting the second halogen species in the first semiconductor substrate to a second depth that is less than the first depth, and
• the first halogen species has a higher diffusion coefficient with respect to silicon than the second halogen species.

A photodetector comprising:

• a first semiconductor substrate;
• detection regions comprising epitaxial germanium (Ge) and disposed in recesses formed in a front side surface of the first semiconductor substrate;
• a first halogen species implanted in the first semiconductor substrate around the recesses;
• and
• barrier layers surrounding the recesses and comprising a second halogen species, wherein the barrier layers are configured to reduce diffusion of the first halogen species into the detection regions from the first semiconductor substrate,
• wherein the first halogen species has a smaller atomic radius than the second halogen species.