Stressed field effect transistor and methods for its fabrication

A stressed field effect transistor and methods for its fabrication are provided. The field effect transistor comprises a silicon substrate with a gate insulator overlying the silicon substrate. A gate electrode overlies the gate insulator and defines a channel region in the silicon substrate underlying the gate electrode. A first silicon germanium region having a first thickness is embedded in the silicon substrate and contacts the channel region. A second silicon germanium region having a second thickness greater than the first thickness and spaced apart from the channel region is also embedded in the silicon substrate.