A methodology for (a) the etching of films of Al2O3, HfO2, ZrO2, W, Mo, Co, Ru, SiN, or TiN, or (b) the deposition of tungsten onto the surface of a film chosen from Al2O3, HfO2, ZrO2, W, Mo, Co, Ru, Ir, SiN, TiN, TaN, WN, and SiO2, or (c) the selective deposition of tungsten onto metallic substrates, such as W, Mo, Co, Ru, Ir and Cu, but not metal nitrides or dielectric oxide films, which comprises exposing said films to WOCl4 in the presence of a reducing gas under process conditions.