A method for forming a stacked semiconductor structure comprises providing a first chip comprising a plurality of first active circuits and a first aluminum connection pad, depositing a first dielectric layer on a first side of the first chip, forming a first copper bonding pad on the first aluminum connection pad, providing a second chip comprising a plurality of second active circuits, depositing a second dielectric layer on a first side of the second chip, forming a second copper bonding pad in the second dielectric layer, stacking the first chip on the second chip, wherein the first copper bonding pad is in direct contact with the second copper bonding pad and bonding the first chip and the second chip to form a uniform bonded feature.