Corrosive Behavior of Tungsten in Post Dry-Etch Residue Remover

Failure of the tungsten (W) plug has become the main reliability issue in post-metal-etch cleaning due to the interaction between tungsten and the alkanolamine or hydroxylamine ingredients in the cleaning solution, as well as tungsten and chloride from the previous chlorine-based etching process. In our efforts to understand tungsten plug corrosion, the electrochemical behavior of blanket tungsten films in the post-etch resist remover, the EKC265 solution, at 65 °C in the presence of deionized water and Cl- was investigated using Tafel extrapolation, potentiometry, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The corrosion-current density and the open-circuit potential data showed that the basic EKC265 solution was aggressive to tungsten. The addition of chloride ions (Cl-) and the deionized water to the EKC265 solution further increased the corrosion-current density and shifted the open-circuit potential to more negative values. SEM pictures gave visual evidence of changes on the tungsten surface due to corrosion. Pitting was observed in the presence of both deionized water and Cl-. The changes in the chemical composition of tungsten films were evaluated with XPS. It was found that the distribution of oxidation states of tungsten was largely influenced by the chemical treatment in the EKC265-based electrolytes and closely related to the corrosion resistance of tungsten in the electrolytes.