Abstract
An integrated circuit includes a gate electrode and spacers along sidewalls of the gate electrode. The integrated circuit further includes a source/drain (S/D) region adjacent to the gate electrode. The S/D region includes a diffusion barrier structure at least partially in a recess of the substrate. The diffusion barrier structure includes an epitaxial layer having a first region and a second region. The first region is thinner than the second region, and the first region is misaligned with respect to the sidewalls of the gate electrode. The S/D region includes a doped silicon-containing structure over the diffusion barrier structure. The first region of the diffusion barrier structure is configured to partially prevent dopants of the doped silicon-containing structure from diffusing into the substrate. The second region of the diffusion barrier structure is configured to substantially completely prevent the dopants of the doped silicon-containing structure from diffusing into the substrate.