Mechanical properties of Cu electroplated in supercritical CO2 emulsion evaluated by micro-compression test

• Cu film and Cu micro-pillar where fabricated using supercritical CO2 emulsion (SCE).
• Cu electroplating with SCE (EP–SCE) does not raise any impurity problems.
• Grain refinement was observed for the Cu film fabricated by EP–SCE.
• Increase in strength was observed for the Cu film fabricated by EP–SCE.
• The increase in strength is considered to come from grain refinement strengthening.

This paper reports mechanical properties of Cu films fabricated by electroplating with supercritical CO2 emulsion (EP–SCE). Also, mechanical properties of Cu films fabricated by conventional electroplating (CONV) were evaluated to examine the effects of EP–SCE. The films were electroplated in an electrolyte composed of copper sulfate plating bath, supercritical CO2 and surfactant. Scanning ion microscopy images confirmed the supercritical CO2 emulsion refined microstructure of the plated Cu from about 1 μm of grain size in CONV to about submicron order of grain size in EP–SCE. Non-tapered micro-sized Cu pillars were prepared by focused ion beam and used in the micro-compression test. Strengths of the Cu films fabricated by EP–SCE were 300 MPa, which is higher than the CONV case. Impurity concentration in the films was evaluated by glow discharge optical emission spectroscopy, and no significant difference between EP–SCE and CONV was observed. The high strength in EP–SCE is believed to be mainly a result of grain refinement strengthening.

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