COMPLEMENTARY METAL OXIDE SEMICONDUCTOR INTEGRATED CIRCUIT USING UNIAXIAL COMPRESSIVE STRESS AND BIAXIAL COMPRESSIVE STRESS

摘要

A transistor may be formed of different layers of silicon germanium, a lowest layer having a graded germanium concentration and upper layers having constant germanium concentrations such that the lowest layer is of the form Si1-xGex. The highest layer may be of the form Si1-yGey on the PMOS side. A source and drain may be formed of epitaxial silicon germanium of the form Si1-zGez on the PMOS side. In some embodiments, x is greater than y and z is greater than x in the PMOS device. Thus, a PMOS device may be formed with both uniaxial compressive stress in the channel direction and in-plane biaxial compressive stress. This combination of stress may result in higher mobility and increased device performance in some cases.