Die structures and methods of forming the same

Die structures and methods of forming the same are described. In an embodiment, a device includes: a lower integrated circuit die; a first upper integrated circuit die face-to-face bonded to the lower integrated circuit die, the first upper integrated circuit die including a first semiconductor substrate and a first through-substrate via; a gap-fill dielectric around the first upper integrated circuit die, a top surface of the gap-fill dielectric being substantially coplanar with a top surface of the first semiconductor substrate and with a top surface of the first through-substrate via; and an interconnect structure including a first dielectric layer and first conductive vias, the first dielectric layer disposed on the top surface of the gap-fill dielectric and the top surface of the first semiconductor substrate, the first conductive vias extending through the first dielectric layer to contact the top surface of the first through-substrate via.