Arc-shaped fin top forming method and fin field effect transistor

The invention discloses an arc-shaped fin top forming method and a fin field effect transistor. The method comprises the following steps that: a fin structure is provided; atomic layer etching is carried out on the top of the fin structure, and whether etching is carried out again is determined according to the etching amount of the fin structure; if yes, atomic layer etching on the top of the fin structure continues to be executed, and whether the etching process is conducted again or not is determined according to the etching amount of the fin structure; and if not, etching is stopped. The atomic layer etching process is circularly executed on the top of the fin structure to form the arc-shaped fin top, although the etching rate of the circulating process is lower than that of an existing mode, the circulating process does not damage the surface, and the pattern size and the loading density can be minimized. As the surface is not damaged, charge trapping is not formed, and the electrical characteristics of