The invention discloses a
fin field effect transistor forming method. The method comprises steps: a
semiconductor substrate is provided, wherein the
semiconductor substrate is provided with a gate structure dense region and a gate structure sparse area, and the surface of the
semiconductor substrate is provided with convex fin parts
and gate structures crossing the fin parts; a side
wall material layer is formed, and the side
wall material layer coats the fin parts and the gate structures; first
etching is carried out on the side
wall material layer, first side walls are formed at two sides of the fin parts in the gate structure dense region, second side walls are formed at two sides of the fin parts in the gate structure sparse region, and the first side walls and the second side walls are lower than the top surfaces of the fin parts; second
etching is carried out on fin parts at two sides of the gate structures, first fin parts are formed, the first side walls are flush with the first fin parts, and the second side walls are higher than the first fin parts; third
etching is carried out to reduce the
height difference between the second side wall and the first fin part; and source and drain areas are formed on the first fin part. The
fin field effect transistor forming method of the invention can improve the performance of the
fin field effect transistor.