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 H2 O2 or Fe (N O3) 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 (N O3) 3 is relatively dense and therefore passive, whereas that formed in the H2 O2 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.