“zero-undercut” semi-additive copper patterning - a breakthrough for ultrafine-line RDL lithographic structures and precision RF thinfilm passives

This paper presents the first demonstration of a “zero-undercut” precision formation of ultrafine-line copper conductor patterns for redistribution layers (RDL) and thin film RF passives. This is accomplished by using a highly-anisotropic and uniform copper plasma-etching process to remove the seed layer with no lateral etching of the copper patterns, unlike what is seen with traditional seed-layer removal by wet-etching. Application of this technical breakthrough for large-area panel processes allows demonstration of precision copper patterns demonstrated, for the first time, on organic laminates with no measurable lateral undercut. Two different plasma chemistries, one pure physical sputter-etching, and the other based upon chemical-physical processes with a hydrogen plasma, were investigated and compared.