Effect of Electrolyte Acidity on Copper Plating Process Performance

The effect of sulfuric acid concentration in copper electroplating has been evaluated for semiconductor interconnect fabrication. Gapfill rates and defect densities were determined for 10, 80, and 175 g/l sulfuric acid concentration. The results show an increase in bottom growth rate with increased acidity in addition to a shape change in the film growth front. Chonopotentiometry was used to study the effect of acidity on organic additive responses in these electrolytes. Opposed to low acid chemistry, the suppressor becomes mass transport limited at higher acidity, suggesting concentration gradients could be related to the gapfill differences observed. Defect densities for low acid chemistry were found somewhat higher than for high acid electrolyte. This could be caused by differences in wetting behavior between chemistries.