SEMICONDUCTOR DEVICE WITH MULTIPLE SEMICONDUCTOR LAYERS

摘要

A semiconductor device structure (10) uses two semiconductor layers (16 & 20) to separately optimize N and P channel transistor carrier mobility. The conduction characteristic for determining this is a combination of material type of the semiconductor, crystal plane, orientation, and strain. Hole mobility is improved in P channel transistors (38) when the conduction characteristic is characterized by the semiconductor material being silicon germanium, the strain being compressive, the crystal plane being (100), and the orientation being <100>. In the alternative, the crystal plane can be (111) and the orientation in such case is unimportant. The preferred substrate for N-type conduction is different from the preferred (or optimum) substrate for P-type conduction. The N channel transistors (40) preferably have tensile strain, silicon semiconductor material, and a (100) plane. With the separate semiconductor layers (16 & 20), both the N and P channel transistors (38 & 40) can be optimized for carrier mobility.