A structure comprises a first semiconductor substrate, a first bonding layer deposited on a bonding side the first semiconductor substrate, a second semiconductor substrate stacked on top of the first semiconductor substrate and a second bonding layer deposited on a bonding side of the second semiconductor substrate, wherein the first bonding layer is of a horizontal length greater than a horizontal length of the second semiconductor substrate, and wherein there is a gap between an edge of the second bonding layer and a corresponding edge of the second semiconductor substrate.