On-line detection of additive concentrations in acidic copper plating solution for metal interconnection by an electrochemical microfluidic workstation†

On-line detection of additive concentrations in acidic copper (Cu) electroplating solution, including the suppressor, accelerator and leveler, is crucial for the industrial production of integrated circuit metal interconnections. For this purpose, a portable electrochemical microfluidic workstation (EMW) is developed. The polymer electrochemical microfluidic chip is designed and fabricated by 3D printing, in which a liquid mixer is integrated with an electrochemical microcell. The asymmetrically distributed herringbone microstructures in the microchannels (width: 400 μm, height: 300 μm, length: 4 cm) ensure the highly efficient mixture of solutions. In the electrochemical microcell, a 12.5 μm radius platinum ultramicroelectrode (Pt UME) acts as the working electrode. Based on the suppressing or accelerating effects of the additives on Cu electroplating, the calibration curves can be obtained by the stripping charge of electrodeposited Cu. Thus, the concentration of each additive in the acidic Cu electroplating solution can be detected on line and adjusted in time. The solution volume needed for each additive is approximately 220 μL. The detection error is lower than 10%, meeting the analytic requirements in industry. The automated EMW has the potential to replace the current manual cyclic voltammetry stripping (CVS) employed in lab analysis.

Keywords: Electrochemical microfluidic workstation; On-line detection of additive concentration; Microfluidic chip; Ultramicroelectrode; Acidic copper electroplating.