Integrated circuits and methods of forming integrated circuits

An integrated circuit comprising:

• a gate electrode over a substrate;
• and
• a source/drain (S/D) region adjacent to the gate electrode, the S/D region comprising:
• a diffusion barrier structure at least partially in a recess of the substrate, wherein the diffusion barrier structure comprises an epitaxial layer, wherein the epitaxial layer comprises a first region and a second region, wherein the first region is thinner than the second region, and a first portion of the first region extends underneath the gate electrode;
• and
• a doped silicon-containing structure over the diffusion barrier structure, wherein 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 and 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.

An integrated circuit comprising:

• a gate electrode over a substrate;
• spacers along sidewalls of the gate electrode;
• and
• a source/drain (S/D) region adjacent to the gate electrode, the S/D region comprising:
• a diffusion barrier structure at least partially in a recess of the substrate, wherein the diffusion barrier structure comprises an epitaxial layer, wherein the epitaxial layer comprises a first region and a second region, wherein the first region is thinner than the second region, and a first portion of the first region under the spacers;
• and
• a doped silicon-containing structure over the diffusion barrier structure, wherein the doped silicon-containing structure extends underneath at least a portion of the spacers, 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 and 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.