Silicon-carbon (Si:C) is one materials choice for creating a uniaxial tensile stressor via epitaxy in the source/drain region of NMOS transistors. The concept of using Si:C is to epitaxially deposit a material with a smaller lattice constant than Si within the recessed source/drain regions of the transistor to induce tensile strain in the adjacent channel region. However, epitaxy of Si:C is much more challenging than SiGe on the process conditions. 

First, due to the low solubility of carbon in silicon, it is necessary to grow the epitaxial layers at low temperatures (<600°C) to ensure that the carbon atoms occupy substitutional sites. The impact of this low temperature requirement is that the growth rate using traditional silicon precursors (silane, disilane, dichlorosilane) is reduced, requiring longer processing times per wafer. The low temp high Gr precursors to be discussed are Silcore (trisilane), dichlorodisilane, and digermylmethane. For low temperature deposition silicon precursor it maybe forms a reactive intermediate that has a high sticking coefficient and is not limited by the rate of hydrogen desorption from silicon. 

Another impact of the low temperature requirement is the ability to create a selective process since the etch rate of silicon using HCl also decreases with decreasing temperature.