A method for forming shallow trench isolations includes the steps of defining a wafer substrate, forming a silicon dioxide insulating layer on the substrate, depositing a silicon nitride layer on the silicon dioxide insulating layer, and forming at least one trench in the substrate through the silicon dioxide and silicon nitride layers. The method also includes the steps of depositing a silicon dioxide layer over the silicon nitride layer and in the trench, removing the silicon dioxide layer deposited over the silicon nitride layer, anisotropically etching the silicon dioxide layer to produce silicon dioxide sidewalls in the trench contiguous with the silicon nitride layer, isotropically etching to remove the sidewalls and removing the silicon nitride layer.