In-situ transmittance measurement for characterization of organic additives in Cu electroless deposition

• In-situ transmittance measurement was suggested to evaluation solution performances.
• In-situ monitoring could show the reactivity of solution and properties of Cu particles.
• Results from in-situ monitoring and film deposition showed a close relationship.

As a simple tool for the evaluation of solution performance, in-situ transmittance measurement was employed to investigate the functionality of the organic additives in Cu electroless deposition (ELD) on a Pd catalyst. Sulfur based additives of bis(3-sulfopropyl)disulfide (SPS) and poly(ethylene glycol) with various molecular weights exhibited an acceleration and suppression effect depending on the concentration and molecular weights. The effects of these additives on the reactivity of solutions corresponded to the results from the Cu film deposition on a Ta substrate. In particular, the Cu particle obtained from in-situ transmittance measurement also allowed us to forecast both the reactivity of solution and the properties of the Cu film. Although the precise prediction of properties was difficult, the characteristics of the Cu particle and the Cu film have a close relationship to the grain size and surface roughness. It was confirmed that the in-situ monitoring of transmittance changes was feasible to estimate the reactivity of solution in the presence of organic additives, and the Cu particle which is product from this method indicated the features of the Cu film. Therefore, in-situ transmittance measurement would be an applicable method to figure out the solution performance and the prediction of Cu properties.