In this patent application Canon details what appears to be a BSI sensor and how to manufacturer it. BSI sensors "look" different in the atypical cross section views between that and a regular sensor.
On a regular sensor wiring go up, through and around each pixel. Why this is the way it is is probably way above my pay grade. On a BSI (back side illuminated) sensor all the wiring is underneath the actual pixel. This is how you can look at a cross section of a patent application like and fairly readily determine what type of sensor they are working on.
This patent application deals with problematic dark current especially when the pixels become smaller, and details a method of manufacturing a high density BSI sensors (high MP's) that have a method of resolving this through the isolation layers between each pixel.