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., E_e/E_t) of the location. Using a ratio higher than 1.5 results in hollow tubes, whereas a ratio less than 1.0 produces dense pillars.