Forming method of N-type fin field effect transistor

The invention provides a forming method of an N-type fin field effect transistor. The method comprises the steps that a semiconductor substrate is provided, wherein the semiconductor substrate is provided with fins; a gate structure stretching across the fins is formed; each fin comprises a first side wall covered by the gate structure and a second side wall opposite to the first side wall; first ion implantation is carried out on the first side walls of the fins at two sides of the gate structure; first annealing treatment is carried out on the fins subjected to first ion implantation; after the first annealing treatment, second ion implantation is carried out on the second side walls of the fins at two sides of the gate structure; second annealing treatment is carried out on the fins subjected to the second ion implantation; and after the second annealing treatment, a source and a drain are formed on the surfaces of the fins at two sides of the gate structure respectively. By the method provided by the invention, the performance of the N-type fin field effect transistor can be improved.