Study of dynamics of diffusion and cluster formation of copper deposition on polyimide by optical second‐harmonic generation

We demonstrate that optical second‐harmonic generation (SHG) can be successfully used for in situ study of metal/polymer interfaces. With this SHG technique, Cu cluster formation on polyimide by surface diffusion and Cu diffusion into polyimide have been investigated. The diffusion coefficients of Cu clusters into polyimide at various temperatures have been determined from the measured decay of SHG signal with time. The effects of temperature, cluster size, and surface modification on diffusion have also been examined. For T < Tg, the surface diffusion of Cu on polyimide to form clusters dominates over the diffusion into the bulk. The latter process becomes competitive with increasing temperature. When T ≳ Tg, few large‐size Cu clusters can be formed on the polyimide surface. Cu diffusion into polyimide bulk can be greatly impeded by either a monolayer of Ti or by Cu clusters implanted in polyimide beforehand. In this case, Cu can wet the modified surface and form an interface between Cu and polyimide wit...