Abstract: A method includes bonding a capacitor die to a device die. The device die includes a first semiconductor substrate, active devices at a surface of the first semiconductor substrate, a plurality of low-k dielectric layers, a first dielectric layer over and contacting a top low-k dielectric layer in the plurality of low-k dielectric layers, and a first plurality of bond pads in the first dielectric layer. The capacitor die includes a second dielectric layer bonding to the first dielectric layer, a second plurality of bond pads in the second dielectric layer and bonding to the first plurality of bond pads, and a capacitor electrically coupled to the second plurality of bond pads. After the capacitor die is bonded to the device die, an aluminum-containing pad is formed over the capacitor die and electrically coupled to the device die. A polymer layer is formed over the aluminum-containing pad.