Semiconductor structure and forming method thereof

The invention discloses a semiconductor structure and a forming method thereof, and the method comprises the steps: providing a substrate, forming a first semiconductor layer and a second semiconductor layer which are located in different regions of the substrate on the surface of the substrate, and enabling the first semiconductor layer and the second semiconductor layer to be made of different materials; the first semiconductor layer and the second semiconductor layer are patterned, the first semiconductor layer remaining on the substrate serves as a first fin part, the second semiconductor layer remaining on the substrate serves as a second fin part, and the wall thickness of the first fin part is larger than that of the second fin part; forming a protection layer covering the second fin part; and after the protection layer covering the second fin part is formed, removing part of the side wall of the first fin part, so that the difference between the wall thickness of the first fin part after the part of t