Optimizing the lithographic patterning effect in an acid copper electroplating process

The effects of the average cathodic current density, electrode separation, and the active area density on the workpiece-level plating thickness variability were studied by factorial experiments for an acid copper pattern electroplating process. All the three parameters and the current density×electrode separation interaction were found to be significant, and an 8-term first-order prediction model was constructed and verified experimentally. The minimum variability achievable was found to increase with the active area density contrast over the board surface, and was explained by the scattering effect of the density contrast on the average plating thickness. A subsequent verification run using a simple circuit pattern showed that a composite parameter involving the overall active area density, the continuum area and the number of density contrasts, was appropriate. The possibility of further reducing the workpiece level variability by investigating the interaction effect between the overall active area density and the density contrast of the substrate was suggested.