On the structure of micrometer copper features fabricated by intermittent micro-anode guided electroplating

Micrometer copper features were fabricated by an intermittent micro-anode guided electroplating (MAGE) process and revealed different structures depending upon the experimental conditions. A hollow microtube was developed at 4.0 V with an initial distance of 2 μm/step. By decreasing the voltage from 4.0 to 3.2 V while increasing the initial distance from 2 to 25 μm/step, a dense copper column with a smooth surface was formed instead of a rough-surfaced tube. The dense column was prepared on a base with larger area compared to that used for the hollow tube. The observation of different structures by electrochemical deposition could be explained using a quantitative model based on finite element analysis. According to this model, the structure is determined by the ratio of field strength at the periphery to that in the center (i.e., Ee/Et) of the location. Using a ratio higher than 1.5 results in hollow tubes, whereas a ratio less than 1.0 produces dense pillars.