The dopant in the source/drain regions 82 of FIG. 17B may diffuse into the channel region of the FinFET device 100. The increased carrier concentration in the channel region (due to dopant diffusion) may reduce the threshold voltage. For various reasons, such as the source/drain regions having different dopant concentrations at different locations (e.g., in layers L1, L2 and L3), the concentration of the diffused dopant in the channel region may be non-uniform, which may result in a non-uniform threshold voltage for the FinFET device 100. As discussed above with reference to FIG. 6, the germanium concentration in the channel region may be tuned in accordance with the concentration of the diffused dopant in the channel region, such that a uniform threshold voltage may be achieved. For example, a lower concentration of germanium may be formed in an area with higher dopant (e.g., boron) concentration, and a higher concentration of germanium may be formed in an area with a lower dopant (e.g., boron) concentration.
