CMOS image sensor with heat management structures

A complementary metal-oxide semiconductor (CMOS) image sensor, comprising:

• a device wafer substrate of a device wafer;
• a device layer of the device wafer disposed on a frontside of the device wafer substrate in which a plurality of photosensitive elements are disposed, wherein the photosensitive elements are sensitive to light incident on a backside of the device wafer substrate;
• a metal stack including metal layers separated by an inter-metal dielectric, the metal stack disposed over the frontside of the device wafer substrate with the device layer disposed between the metal stack and the device wafer substrate;
• a second wafer bonded over the metal stack;
• and
• a heat sink disposed entirely through the second wafer and extending into the metal stack of the device wafer to conduct heat from the device layer of the device wafer through the metal stack and the second wafer to a top surface of the second wafer, wherein the heat sink further includes:
• metal vias within the metal stack interconnecting the metal layers,
• wherein one of the metal vias forms a contact that extends to the device layer to conduct heat away from the device layer of the device wafer to the top surface of the second wafer.