WIPO published Omnivision patent applications WO/2009/099778 and WO/2009/100039 on BSI photodiode profile and WO/2009/100038 on black pixels in BSI technology. While the black pixel idea is quite obvious - removing photodiode implants to make black pixel light-insensitive, a really interesting part of these applications is Omnivision BSI pixel cross-section:
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.