Mechanisms of photoresist dissolution

The comprehensive physical picture developed describes the dissolution of a broad range of materials, including novolak-based photoresists and can be applied to the dissolution in aqueous base of both small molecules and polymers that can ionize. The model was verified by measuring the dissolution of solute-coated spinning discs. Key experimental variables included the flow (as a Reynolds number) and the base concentration, which was in this case of sodium hydroxide. The physical and chemical characteristics of the dissolving species determine the rate-limiting steps, which cause different dissolution behavior. The dissolution of low molecular weight phenolic resin is controlled by a combination of solute release and solute mass transfer, without the formation of any significant intermediate gel phase. Several other dissolution mechanisms are rationalized based on a simple “strings of buoys” analogy, which can be extended to other cases as well.