Oxidation behavior of tungsten in H2O2- and Fe(NO3)3-base aqueous slurries

By using potentiodynamic scanning and cyclic voltametry, the oxidation and dissolution kinetics of tungsten/tungsten-oxides were investigated in the chemical mechanical planarization (CMP) slurries containing either H2O2 or Fe (NO3)(3) as an oxidant. The microstructure of the tungsten/tungsten-oxide surface and its temporal and depth variation of the chemical state were also examined by scanning electron microscopy and X-ray photoelectron spectroscopy. Through the analysis, it is shown that the oxide layer formed in the slurry containing Fe (NO3)(3) is relatively dense and therefore passive, whereas that formed in the H2O2 slurry is a porous tungsten oxide film which would not protect the underlying tungsten from further chemical etching. The electrochemical responses of tungsten surfaces in the two different oxidant conditions were compared, and a significant difference in the CMP performance due to the microstructure and chemical state variation of the tungsten surface was observed. (c) 2006 The Electrochemical Society.