US Patent 12080709 Dual inner spacer epitaxy in monolithic stacked FETs

A semiconductor device includes a bottom device, a top device, and a spacer. The bottom device includes a first set of silicon sheets and a first source-drain epitaxy in direct contact with the first set of silicon sheets. The top device includes a second set of silicon sheets, a set of separation layers, and a second source-drain epitaxy. Each silicon sheet of the second set of silicon sheets is separated by a separation layer of the set of separation layers. The second source-drain epitaxy is arranged in direct contact with the second set of silicon sheets. The spacer is arranged between the first source-drain epitaxy and the second source-drain epitaxy and is arranged between each silicon sheet of the second set of silicon sheets.