ELECTROCHEMICAL MEASUREMENTS DURING THE CHEMICAL-MECHANICAL POLISHINGOF 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 t he presence of various oxidants. Of the different oxidants tested at p H 1.5 or pH 4.4, (NH4)(6)Mo7O24 formed the most protective passive lay er on tungsten. Even in the presence of the most aggressive oxidant, F e(NO3)(3), the dissolution rates of chemical vapor deposited tungsten were approximately 3 nm/min during abrasion, which is a very small fra ction of typical removal rates reported for chemical mechanical polish ing of tungsten. This indicates that electrochemical oxidation followe d by abrasive removal of the oxidation product and dissolution may not be the primary mechanism for tungsten removal. Atomic force microscop y scans of polished tungsten films indicate that corrosion assisted fr acture may be an important removal mechanism for tungsten during chemi cal mechanical polishing.