Electrochemical measurements during the chemical mechanical polishing of tungsten thin films

A polishing tool and a potentiostat were used to simultaneously polish and measure the direct current (de) open-circuit potential and anodic polarization behavior of chemical vapor deposited tungsten films in the presence of various oxidants. Of the different oxidants tested at pH 1.5 or pH 4.4, (NH4)(6)Mo7O24 formed the most protective passive layer on tungsten. Even in the presence of the most aggressive oxidant, Fe(NO3)(3), the dissolution rates of chemical vapor deposited tungsten were approximately 3 nm/min during abrasion, which is a very small fraction of typical removal rates reported for chemical mechanical polishing of tungsten. This indicates that electrochemical oxidation followed by abrasive removal of the oxidation product and dissolution may not be the primary mechanism for tungsten removal. Atomic force microscopy scans of polished tungsten films indicate that corrosion assisted fracture may be an important removal mechanism for tungsten during chemical mechanical polishing.