Abstract: In accordance with various embodiments of the disclosed subject matter, a shallow trench isolation structure and a fabricating method thereof are provided. The method for forming the shallow trench isolation structure may include: providing a semiconductor substrate; forming a shallow trench in the semiconductor substrate; forming a first insulating layer on a surface of the semiconductor substrate and in the shallow trench, a portion of the first insulating layer in the shallow trench includes an opening; etching the first insulating layer to increase a width of the opening; after etching the first insulating layer, performing a plasma treatment to an exposed surface of the first insulating layer; after the plasma treatment, cleaning the surface of the first insulating layer; and after cleaning the surface of the first insulating layer, filling a second insulating layer into the shallow trench.