FIG. 25A illustrates the simulated threshold voltage Vt of a FinFET device with dopant diffusion. The FinFET device of FIG. 25A does not counteract the effect of the dopant diffusion with a non-uniform germanium concentration in the channel region. In FIG. 25A, the y-axis illustrates the threshold voltage, and the x-axis illustrates the vertical distance (e.g., depth) between the top surface of the fin and the location in the channel region being measured. As illustrated in FIG. 25A, the FinFET device has a non-uniform threshold voltage.

FIG. 25B illustrates the germanium concentration in the channel region of an embodiment FinFET device. The germanium concentration is designed to counteract the effect of the diffused dopant (see FIG. 25A) in the channel region. FIG. 25C illustrates the simulated threshold voltage of the embodiment FinFET device, which shows a uniform threshold voltage.

Referring back to FIGS. 17C and 17D, as a result of the epitaxy processes used to form the epitaxial source/drain regions 82 in the region 50B and the region 50C, upper surfaces of the epitaxial source/drain regions have facets which expand laterally outward beyond sidewalls of the fins 58. In some embodiments, these facets cause adjacent source/drain regions 82 of a same FinFET device to merge as illustrated by FIG. 17C. In other embodiments, adjacent source/drain regions 82 remain separated after the epitaxy process is completed as illustrated by FIG. 17D.