SEMICONDUCTOR DEVICE HAVING STRAINED SILICON AND SILICON GERMANIUM ALLOY LAYERS

摘要

A CMOS (complementary metal-oxide-silicon) heterojunction semiconductor device is formed by growing a virtual substrate (1) of silicon-germanium alloy on a silicon wafer (2), the silicon wafer (2) being in a relaxed state and the silicon-germanium alloy of the virtual substrate (1) having the formula Si1-xGex, where x varies between 0 and 0.25, and is typically 0.15. A first conduction layer (3) of silicon-germanium alloy having the formula Si1-yGey, where y is less than x+0.3 is then grown on the relaxed silicon-germanium substrate (1). Because of the higher average germanium density in first conduction layer (3) compared with virtual substrate (1), the separation of atoms in layer (3) is less than in virtual substrate (1), as a result of which layer (3) is under compressive strain. This significantly increases the conductivity of the layer (3) to holes compared with a relaxed layer (i.e. not under compressive strain) of the same material. A second conduction layer (4) of silicon is then grown on silicon-germanium alloy layer (3). Because the separation of silicon atoms is less than in silicon-germanium, the silicon layer (4) is placed under tensile stress, which significantly increases the conductivity of layer (4) to electrons.