Assessing the degree of localization in localized electrochemical deposition of copper

The localization of localized electrochemical deposition (LECD) was investigated using the microanode-guided electroplating ( MAGE) technique. Two modes (i.e., one-step and intermittent-step) of the MAGE process were employed to explore the circular area around the bottom of the copper microcolumns deposited on a substrate. The diameter was utilized to estimate the localization occupied by the column instead of using the bottom area. For the hillocks deposited by one-step MAGE, the localization diameter increases with increasing the electric biases between the microanode and the substrate. For the copper microcolumns fabricated by intermittent-step MAGE, the localization diameter increases to a critical magnitude and levels off upon increasing the height of the columns. The critical localization diameter was found to be dependent on the electric biases and the initial gap between the microanode and the top of the microcolumn deposited earlier. The less the electric biases and the initial gap in intermittent MAGE, the smaller the localization diameter of the microcolumn. A model is proposed to illustrate the localization defined by one-step MAGE and the critical localization diameter (D-c) obtained from intermittent-step MAGE. A relationship between the ratio of the conical core strength to the conical periphery strength (i.e., E-core/E-p) and the electric bias has been established for the critical localization diameter of the microcolumns. The strength ratio can be used as a criterion to predict whether a localization diameter increases or not.