Method of fabricating multi-wafer image sensor

A method of fabricating an image system, the method comprising:

• forming a pixel array in an imaging region of a semiconductor substrate;
• forming a trench in a peripheral region of the semiconductor substrate after forming the pixel array, wherein the peripheral region is on a perimeter of the imaging region;
• filling the trench with an insulating material;
• forming an interconnect layer spanning the imaging region and the peripheral region after filling the trench with the insulating material, wherein a first wafer includes the interconnect layer and the semiconductor substrate;
• bonding the first wafer to a second wafer;
• thinning a backside of the semiconductor substrate to expose the insulating material;
• forming a via cavity through the insulating material, wherein the via cavity extends down to a second interconnect layer of the second wafer;
• and
• filling the via cavity with a conductive material to form a via, wherein the insulating material electrically insulates the conductive material from the semiconductor substrate.