Back-Side Illuminated Image Sensor Doped Epitaxial Isolation

The patent replaces the mechanical ion implantation process with a chemical epitaxial growth process. Instead of physically implanting ions into the substrate to create doped regions, the invention uses in-situ epitaxial growth to form doped semiconductor layers conformally on the trench walls. This substitution eliminates the damage and defects caused by ion bombardment while achieving the same electrical isolation function.

The patent changes the fundamental process parameter from ion implantation (physical method) to epitaxial growth (chemical method). This parameter change allows for controlled doping during the growth process itself, enabling the formation of doped regions without the harmful effects of ion implantation, while maintaining precise control over dopant concentration and distribution.

The patent applies local quality by forming doped regions specifically on the trench walls adjacent to each pixel, rather than uniformly doping the entire substrate. This localized doping approach provides enhanced isolation precisely where needed between shrinking pixels, addressing dark current and cross-talk issues at the specific locations where pixel density increases create problems.

The patent performs preliminary action by forming the deep trench isolation structures and doped regions before final pixel fabrication. This early establishment of isolation barriers ensures that even as pixels are later reduced in size, the dark current and cross-talk control is already in place, preventing degradation of performance as pixel density increases.