Method for forming shallow trench isolation (STI) structure

The invention discloses a method for forming a shallow trench isolation (STI) structure. The method comprises the following steps: forming a pad oxide layer and a silicon nitride layer on a semiconductor substrate; patterning the pad oxide layer, the silicon nitride layer and the semiconductor substrate so as to form a trench; forming a lining oxide on the inner surface of the trench; depositing an insulating medium so as to form a trench oxide; then carrying out planarization treatment on the insulating medium; measuring the residual thickness of the silicon nitride layer after the insulating medium is subjected to planarization, and corroding the trench oxide according to the measured residual thickness; and finally, removing the silicon nitride layer and the pad oxide layer so as to form the STI structure. The method provided by the invention has the advantages that through measuring the residual thickness of the silicon nitride layer after the insulating medium is subjected to planarization and selecting