Localized electrochemical deposition of micrometer copper columns by pulse plating

Micrometer copper column fabrication by localized electrochemical deposition (LECD) was investigated in this study. To obtain columns with uniform diameter, compact structure and a smooth surface, LECD conducted in pulse current (PC) mode was better than that conducted in direct current (DC) mode. A micro-reference electrode was used to monitor the potential at the LECD site. Measurement of this potential permitted estimation of the local copper ion concentration resulting from their dynamic consumption by electrochemical reduction and their supply by mass transport. The electroplating current was measured in order to evaluate the rate of electrochemical reduction. The mass-transfer rate of copper ions was estimated using a theoretical calculation based on diffusion. The surface morphology and internal structure were significantly affected by this local concentration, which was in turn governed by the electrical voltage and the duty cycle employed. The mechanism for LECD conducted in PC mode is discussed.