Investigations on the relaxation behavior of metastable tensile strained Si:C alloys

In order to enhance the performance of CMOS transistors, embedded epitaxial layers of Si:C and SiGe are being investigated. It is crucial to the application to avoid strain relaxation of those layers. In this work, a comparative study of the relaxation behavior of tensile strained Si:C layers as well as compressive strained SiGe due to thermal treatment is conducted. For both material systems, the relaxation phenomena were investigated by means of high resolution x-ray diffraction, reciprocal space maps around the 004 and 224 reflexes, as well as AFM and TEM analysis. The relaxation behavior of Si:C was found not to rely on the formation of dislocations as it is the case for SiGe alloys, but on the transition of substitutional carbon to interstitial carbon, or - if the thermal budget is sufficient - the precipitation of Carbides. Although the out of plane lattice constant decreases during the strain relaxation of Si:C layers, the in-plane lattice constant was found to remain unchanged from the as-deposited ones. For both alloys, models to describe the relaxation behavior are proposed.