In some embodiments, in the epitaxy process to form the silicon germanium layer 53, the process condition(s) is tuned such that the concentration of germanium in the silicon germanium layer 53 is non-uniform. In other words, the concentration of germanium at a first location within the silicon germanium layer 53 is different from the concentration of germanium at a second location within the silicon germanium layer 53. The non-uniform concentration of germanium is used to compensate for a non-uniform concentration of dopant (e.g., boron) diffused into the channel region from the source/drain region of the p-type device, thereby resulting in a substantially uniform threshold voltage for the p-type device formed, details of which are discussed hereinafter with reference to, e.g., FIGS. 6-10, 24A, 24B, 25A, 25B, and 25C.

Next, in FIG. 5, fins 58 are formed. The fins 58 are semiconductor strips. In the example of FIG. 5, each of the fins 58 in the region 50C includes three layers, e.g., a bottom layer formed of the material of the substrate 50/50P, a middle layer formed of the material of the epitaxial material 52 (e.g., an epitaxial silicon layer), and an upper layer formed of the material of the silicon germanium layer 53. As illustrated in FIG. 5, each of the fins 58 in the region 50B includes two layers, e.g., a bottom layer formed of the material of the substrate 50/50N, and an upper layer formed of the material of the epitaxial material 52 (e.g., an epitaxial silicon layer). In some embodiments, the fins 58 are formed by etching trenches in the substrate 50 and the epitaxial materials (e.g., 52, 53).