Fine pitch plating resist for high density FO-WLP

Due to large topographic gaps between the chips and mold substrate, the next generation of high density FO-WLP will require fine RDL plating resists that can achieve as low as 2um line/spaces(L/S) with a wider common depth of focus (DOF) margin. In order to meet these requirements, we developed a novel chemically amplified positive tone resist. In this study, we focused on photo acid generators (PAGs) which are one of the major components of chemically amplified resists. We found that controlling the acidity of the generated acid from PAGs after exposure was a key approach to get good profiles on Cu sputtered substrates and wider DOF margins.