Die structures and methods of forming the same

Abstract

In an embodiment, a device includes: a lower integrated circuit die; an upper integrated circuit die bonded to the lower integrated circuit die with a dielectric-to-dielectric bonding region and with a metal-to-metal bonding region; a first buffer layer around the upper integrated circuit die, the first buffer layer including a buffer material having a first thermal conductivity, the buffer material having a columnar crystalline structure, the columnar crystalline structure including crystalline columns having a substantially uniform orientation in a direction that extends away from the lower integrated circuit die; and a gap-fill dielectric over the first buffer layer and around the upper integrated circuit die, the gap-fill dielectric having a second thermal conductivity, the first thermal conductivity greater than the second thermal conductivity.