Toward Tungsten Electrodeposition at Moderate Temperatures Below 100 °C Using Chloroaluminate Ionic Liquids

Abstract

The electrodeposition of tungsten at moderate temperatures (<100 °C) has been of significant interest for the fabrication of thin films and microelectromechanical system components to decrease energy consumption and increase process safety. In this study, we investigated the electrochemical reduction of WCl₄ and WCl₅ in 1-ethyl-3-methylimidazolium chloride (EMIC) and EMIC–AlCl₃ ionic liquids at 80 °C–120 °C. W-rich films with a thickness of approximately 1 μm were obtained from the Lewis acidic EMIC–AlCl₃–WCl₅ bath, whereas the other baths did not yield any deposits. The films obtained from the EMIC–AlCl₃–WCl₅ bath at 80 °C had higher W contents of 54 at.% than those obtained at 120 °C. X-ray absorption near-edge structure spectra of the W-rich films indicated that W existed in an oxidized state. The findings of this study can be used as a guide to explore optimal electrolytes and electrolytic conditions for the electrodeposition of metallic W at moderate temperatures.