Semi-additive Cu-polymer RDL process for interposers applications

This paper explores the possibility to use insulating spin-on dielectric materials for 2.5D interposers. Up to 7 photosensitive materials have been investigated in terms of minimum line/space and via resolution to determine the maximum wiring density. In addition the electrical performances of the best materials were assessed in DC and RF to extract the dielectric constant and loss tangent. Finally the polymer semi-additive process was compared to a Damascene technology using the Wide I/O 2 as case study. The overall performances of each technology are assessed in terms of electrical performances, cost of ownership and wafer bowing. It was shown that the semiadditive process can compete with a conventional Damascene process. The best performing material is a phenol-based polymer, positive tone, aqueous developable, low temperature cure and with a high resolution (up to AR of 1:3).