Abstract
An integrated circuit includes a gate electrode disposed over a substrate. A source/drain (S/D) region is disposed adjacent to the gate electrode. The S/D region includes a diffusion barrier structure disposed in a recess of the substrate. The diffusion barrier structure includes a first portion and a second portion. The first portion is adjacent to the gate electrode. The second portion is distant from the gate electrode. An N-type doped silicon-containing structure is disposed over the diffusion barrier structure. The first portion of the diffusion barrier structure is configured to partially prevent N-type dopants of the N-type doped silicon-containing structure from diffusing into the substrate. The second portion of the diffusion barrier structure is configured to substantially completely prevent N-type dopants of the N-type doped silicon-containing structure from diffusing into the substrate.