A shallow trench isolation structure having a negative taper angle and a method for forming same. A silicon nitride layer formed over a semiconductor substrate is etched according to a plasma etch process to form a first opening therein having sidewalls that present a negative taper angle. The substrate is etched to form a trench therein underlying the first opening. Silicon dioxide fills both the opening and the trench to form the shallow trench isolation structure, with the silicon dioxide in the opening exhibiting a negative taper angle to avoid formation of conductive stringers during subsequent process steps.