Exploratory approaches to the study of acid diffusion and acid loss from polymer films using absorption and fluorescence spectroscopy

As the feature size in microlithography decreases in response to the demand for increasing miniaturization, problems related to acid diffusion and acid loss become more important. In an attempt to address these issues, we have examined various techniques based on absorption and fluorescence spectroscopy. We have synthesized, or developed for applications in this field a range of dyes where their absorption and fluorescence change dramatically as a result of acid-induced changes in their prototropic forms. These dyes represent the basis for an in situ method for quantifying acid in films. Approaches for monitoring acid movement into/out of films have been developed and sate constants for acid loss from poly(vinylphenol) films of various acids at different temperatures have been determined. In an approach to measure acid diffusion, we make use of the fact that fluorescent patterns produced by contact printing. of polymer films containing a dye can be readily resolved by fluorescence microscopy and that diffusion leads to deterioration of these images. In yet another approach, we have used laser photolysis techniques with nanosecond-microsecond resolution to generate acid photochemically and monitor on short time scales its arrival to dye-containing sites within the polymer films.. The advantages and disadvantages of each technique will be discussed, as well as the role of acid, polymer Tg and temperature on acid diffusion/loss.