Three-dimensional semiconductor devices

Abstract

A three-dimensional semiconductor device includes a lower substrate, a plurality of lower transistors disposed on the lower substrate, an upper substrate disposed on the lower transistors, a plurality of lower conductive lines disposed between the lower transistors and the upper substrate, and a plurality of upper transistors disposed on the upper substrate. At least one of the lower transistors is connected to a corresponding one of the lower conductive lines. Each of the upper transistors includes an upper gate electrode disposed on the upper substrate, a first upper source/drain pattern disposed in the upper substrate at a first side of the upper gate electrode, and a second upper source/drain pattern disposed in the upper substrate at a second, opposing side of the upper gate electrode. The upper gate electrode includes silicon germanium (SiGe).