A method of cleanly etching an organic polymer layer disposed over a substrate is disclosed. The invention is particularly useful in damascene processing where openings are etched in the organic polymer layer to form interconnects. The method includes lowering the temperature of the substrate. The method also includes flowing H2O vapor over the organic polymer layer and condensing (or freezing) the H2O vapor on the organic polymer layer. The method additionally includes etching through the organic polymer layer and the condensed H2O vapor to form an opening having a side wall. The condensed (or frozen) H2O vapor is arranged to form a passivating film (of ice) along the side wall of the opening to protect the side wall from etching.