Optimising 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 variab ility were studied by factorial experiments for an acid copper pattern elec troplating process. All the three parameters and the current densityXelectr ode separation interaction were found to be significant, and an 8-term firs t-order prediction model was constructed and verified experimentally. The m inimum variability achievable was found to increase with the active area de nsity contrast over the board surface, and was explained by the scattering effect of the density contrast on the average plating thickness. A subseque nt 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 furth er reducing the workpiece level variability by investigating the interactio n effect between the overall active area density and the density contrast o f the substrate was suggested.