A method for forming a semiconductor structure is provided. The method includes providing a substrate; and forming an ultra-low-dielectric-constant (ULK) dielectric layer on a surface of the substrate. The method also includes etching the ultra-low-dielectric-constant dielectric layer to form a trench in the ultra-low-dielectric-constant dielectric layer; and performing an inert plasma treatment process on a side surface of the trench. Further, the method includes performing a carbonization process on the side surface of the trench; and performing a nitridation process on the side surface of the trench to form a SiCNH layer on the side surface of the trench.