An improved back side illuminated (BSI) complementary metal oxide semiconductor (CMOS) image sensor, and associated methods, improve phase detecting capability. The BSI CMOS image sensor has an array of pixels that include a phase detecting pixel (PDP), a composite grid formed of a buried color filter array and composite metal/oxide grid, and a photodiode implant corresponding to the PDP. A PDP mask is fabricated with a deep trench isolation (DTI) structure proximate the PDP and positioned to mask at least part of the photodiode implant such that the PDP mask is positioned between the composite grid and the photodiode implant.