Chromium as an adhesion promoter/diffusion barrier for Cu on parylene

The low dielectric constant of parylene-n (PA-n) and high conductivity of Cu can provide a low RC time constant interconnection scheme. Vapor deposited PA-n and Partially Ionized Beam (PIB) deposited Cu have been employed for this study. Both Cu and Cr formed plasmas during the PIB deposition. The diffusion of Cu in low concentrations into PA-n at temperatures higher than 350 degrees C has been previously observed. Another problem with high temperature anneals (>300 degrees C) in the Cu/PA-n system is the gradual loss of adhesion. Here, chromium has been demonstrated as a diffusion barrier and adhesion promoter. Previous studies of different systems have used Cr with mixed success as a diffusion barrier. Thus, it is essential to determine its efficiency in the specific Cu/Cr/PA-n system. In this system, thin Cr layers, 1000-100 AA, served as a good barrier and adhesion promoter up to the tested temperature of 350 degrees C. These thin layers are essential to minimize the resistive contribution due to skin effect at high frequencies.<
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