Abstract
A micro-scale pattern transfer method, the Enface technique, has been developed for metal plating and etching. The method involved a patterned tool and substrate brought together in close proximity and a current is passed or voltage is applied between them, enabling metal to be deposited or removed from the substrate selectively. The process requires sufficient electrolyte agitation within an inter-electrode gap of 0.03 cm and has been previously shown to hold in a vertical flow cell, however, for the process to be adapted for tank-type systems for industrial implementation scale-up of agitation is required. It is known that ultrasonic waves can enhance mass transfer during metal electrodeposition. It has therefore been proposed that the use of ultrasonic waves would be an appropriate agitation method for this geometry.
A 20 kHz ultrasonic probe has been shown previously to provide agitation to improve the mass transfer within an inter-electrode gap 0.15 cm during copper electrodeposition in a 500 ml cell (Coleman and Roy, 2014). This same system was used to deposit 4 µm thick features under direct current plating on nickel using an anode with a 1 x 5 mm rectangle feature using a 0.1 M CuSO4 electrolyte. Potential responses were recorded to interrogate the stability of plating conditions, with and without agitation. It was found that at 50% of the limiting current deposited under silent conditions cell potential was less stable and the width of the feature was ~800 µm larger than the tool. It was found that plating using long current pulses with bursts of ultrasound during the off-time provided the most stable potential response, reduced the deposit roughness and improved the adherence of the copper feature to the substrate.
