A method is disclosed for etching an integrated circuit structure within a trench. A layer to be etched is applied over the structure and within the trench. A CF-based polymer is deposited over the layer to be etched followed by deposition of a capping layer of SiOCl-based polymer. The CF-based polymer reduces the width of the trench to such an extent that little or no SiOCl-based polymer is deposited at the bottom of the trench. An O2 plasma etch is performed to etch through the CF-based polymer at the bottom of the trench. The O2 plasma etch has little effect on the SiOCl-based polymer, the thus the upper surfaces of the structure remain covered with polymer. Thus, these upper surfaces remain fully protected during subsequent etching of the layer to be etched.