Semiconductor structure and fabrication method thereof

A semiconductor structure includes a gate structure disposed on a substrate and having an outer spacer, a recess disposed in the substrate and adjacent to the gate structure, a doped epitaxial material filling up the recess, a cap layer including an undoped epitaxial material and disposed on the doped epitaxial material, a lightly doped drain disposed below the cap layer and sandwiched between the doped epitaxial material and the cap layer, and a silicide disposed on the cap layer and covering the doped epitaxial material to cover the cap layer together with the outer spacer without directly contacting the lightly doped drain.