Design and Preliminary Studies of Environmentally Enhanced Water-Castable, Water-Developable Positive Tone Resists: Model and Feasibility Studies

The design of water soluble positive tone resists has been explored using water-soluble poly(2-isopropenyl-2-oxazoline) as the substrate. The overall chemically amplified design incorporates two successive solubility changes to achieve the desired image tone. The initial change in solubility affecting the entire resist film is achieved during the pre-exposure thermal "bake" step, by addition of an appropriately designed carboxylic acid modifier to the matrix. If a diacid is used, crosslinking occurs leading to insolubilization. Alternatively, a monocarboxylic acid may be used to insolubilize the poly(oxazoline) film through a simple polarity switch. The second change in solubility affecting only those areas exposed to radiation is achieved by the photogeneration of acid within the polymer film. Upon post-exposure baking, the photogenerated acid cleaves the carboxylic acid modifier in a process that restores solubility to the polymer matrix. The preparation of a variety of carboxylic acid modifiers and the demonstration of the individual steps of the overall process has been accomplished confirming the validity of this general approach to fully water-soluble positive-tone resists.