Anchor structures and methods for uniform wafer planarization and bonding

An image sensor device comprising:

• a first die comprising:
• a first substrate;
• a first dielectric layer directly on the first substrate;
• a first anchor layer directly on the first dielectric layer;
• a first interconnect structure formed in the first dielectric layer and the first anchor layer;
• and
• a first anchor pad formed in the first anchor layer and directly on the first dielectric layer;
• and
• a second die bonded to the first die, wherein the second die comprises:
• a second substrate;
• a second dielectric layer directly on the second substrate;
• a second anchor layer directly on the second dielectric layer;
• a second interconnect structure in contact with the first interconnect structure, wherein the second interconnect structure is formed in the second dielectric layer and the second anchor layer;
• and
• a second anchor pad formed in the second anchor layer and directly on the second dielectric layer, wherein the first and second interconnect structures, the first and second anchor layers, and the first and second anchor pads are respectively bonded to each other.