In some implementations, the doped amorphous layer is formed on a source region and a drain region of the fin structure, and the doped feature is a lightly doped source and drain (LDD) region disposed in the source region and the drain region of the fin structure. In some implementations, the method further includes forming a gate structure over a channel region of the fin structure before forming the doped amorphous layer. In some implementations, the knock-on implantation process uses argon ions to drive the dopant from the doped amorphous layer into the portion of the fin structure.

Another exemplary method includes forming a fin structure, forming a doped amorphous silicon layer over a portion of the fin structure, and performing a knock-on implantation process to drive a dopant from the doped amorphous silicon layer into the portion of the fin structure, thereby forming a doped feature. In some implementations, the doped amorphous silicon layer wraps a source region and a drain region of the fin structure, and the doped feature is a lightly doped source and drain (LDD) region disposed in the source region and the drain region. In some implementations, forming the doped amorphous silicon layer includes epitaxially growing a semiconductor material over the portion of the fin structure, wherein the semiconductor material is in situ doped during the epitaxially growing.