Image sensor and method for forming the same

Various embodiments of the present disclosure are directed towards an image sensor including first chip and a second chip. The first chip includes a first substrate, a plurality of photodetectors disposed in the first substrate, a first interconnect structure disposed on a front side of the first substrate, and a first bond structure disposed on the first interconnect structure. The second chip underlies the first chip. The second chip includes a second substrate, a plurality of semiconductor devices disposed on the second substrate, a second interconnect structure disposed on a front side of the second substrate, and a second bond structure disposed on the second interconnect structure. A first bonding interface is disposed between the second bond structure and the first bond structure. The second interconnect structure is electrically coupled to the first interconnect structure by way of the first and second bond structures. At least one of the first bond structure and the second bond structure comprises on