One can see that the photodiode extends well underneath the transistor region. Apparently, Omnivision did a great job to achieve lag-free operation with such a complex shape of the fully depleted photodiode.
The earlier Omnivision BSI applications, such as WO/2009/099483, WO/2009/09949, WO/2009/099494, WO/2009/099491 do not mention the extended photodiode profile. By the way, the last of these has an interesting part describing optimizations of the backside implant and the sensor's substrate thickness.
