Electrochemistry of chemical vapor deposited tungsten films with relevance to chemical mechanical polishing

The electrochemical behavior of chemically vapor deposited tungsten films in solutions of interest to tungsten chemical mechanical polishing has been investigated using dc potentiodynamic polarization, linear polarization, and Tafel methods. It was found that in the absence of an oxidizer, the tungsten surface was passivated most effectively at acidic pH values. At pH 2 or 4, a WO₂/WO₃ duplex oxide layer of less than 50 A thickness was detected over the tungsten layer by x-ray photoelectron spectroscopy. The oxide layer formed at pH 2 was much thicker, and had better passivity compared to the oxide formed at pH 4. Addition of H₂O₂ at pH 2 or 4 resulted in a dramatic increase in tungsten dissolution.