Incorporation of sulfur, chlorine, and carbon into electroplated Cu thin films

The microstructure of electroplated Cu thin films and the contamination with incorporated additives were investigated in dependence on the galvanostatic deposition parameters and thermal treatment. Sulfur, chlorine, and carbon were analysed as impurities by TEM, AES and SIMS. SIMS measurements revealed that at room temperature S and Cl show a local stability at their incorporation sites, whereas C is capable to segregate out of the Cu layer. Thermally treated Cu layers indicate a segregation of S and a local stability for incorporated Cl. The incorporation of impurities during Cu deposition is linked with a surface coverage of additives. With increasing time for additive adsorption on the sample surface an increased incorporation of impurities into the growing film occurs. Hence, every start of deposition leads to a significantly high incorporation of S, Cl, and C. The application of aged electrolytes generates very impure Cu layers with an increased film roughness. As a result, the recrystallization of the deposited Cu film is slowed down due to the Zehner pinning effect. The final metallization appears more fine-grained and exhibits worse electrical properties.