A semiconductor device includes a gate stack over a semiconductor substrate, a lightly doped n-type source/drain (LDD) region in the semiconductor substrate and adjacent the gate stack wherein the LDD region comprises an n-type impurity, a heavily doped n-type source/drain (N+ S/D) region in the semiconductor substrate and adjacent the gate stack wherein the N+ S/D region comprises an n-type impurity, a pre-amorphized implantation (PAI) region in the semiconductor substrate wherein the PAI region comprises an end of range (EOR) region, and an interstitial blocker region in the semiconductor substrate wherein the interstitial blocker region has a depth greater than a depth of the LDD region but less than a depth of the EOR region.