Backside illuminated image sensor and method of manufacturing the same

A backside illuminated image sensor comprising:

• a substrate having a frontside surface and a backside surface, and the substrate defining a recess formed in a backside surface portion thereof;
• at least one pixel region disposed in the substrate;
• an insulating layer disposed on the frontside surface of the substrate;
• a bonding pad disposed on a frontside surface of the insulating layer;
• a second bonding pad having a constant thickness and disposed on a bottom surface and an inner side surface of the recess, the second bonding pad defining a second recess formed within the recess and being electrically connected with the bonding pad;
• a third bonding pad formed in the second recess and arranged to fill the second recess;
• and
• an anti-reflective layer disposed on the backside surface of the substrate and the bottom surface and the inner side surface of the recess,
• wherein the second bonding pad is formed on the anti-reflective layer,
• the anti-reflective layer, the substrate and the insulating layer have a first through-hole, a second through-hole and a third through-hole for exposing a portion of a backside surface of the bonding pad, respectively, and
• the second bonding pad comprises a connecting portion formed on inner side surfaces of the first through-hole, the second through-hole and the third through-hole, and the exposed portion of the backside surface of the bonding pad.