Electrodeposition of copper patterns using Enface technique under ultrasonic agitation

This investigation studied different plating modes for the deposition of copper features using the Enface technique, a maskless pattern transfer technology. This novel method can be used for metal deposition of micro-scale features using a patterned anode tool placed in close proximity to the substrate. A current can then be applied which enables metal to be deposited onto the substrate selectively. Previously, a vertical flow cell has been successfully used for this technique; however, a more conventional tank-type system needed investigation for scale-up purposes. Ultrasound was proposed as an appropriate agitation method for this system due to its mass transfer enhancement capabilities. A 20 kHz ultrasonic probe was used as the ultrasound source within a 500 mL cell where 1 × 5 mm copper features were deposited in 0.1 M CuSO<inf>4</inf> using a masked anode. Direct current plating or long current pulses were used and ultrasound agitation was applied either as a continuous wave or using short bursts. The deposit roughness was measured from profiles of the features and scanning electron microscopy was used to study the deposit morphology. Potential responses were recorded to test the stability of plating modes. 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.