Evaluation of Acid Diffusibility in a Chemical Amplification Resist Using Acidic Water-Soluble Film

A new method is proposed to evaluate the acid diffusibility in a chemical amplification resist using acidic overcoat film. This method is easy and effective for both positive- and negative-tone resists and is not influenced by the uncertainty in optical images. The acid diffusion coefficient was estimated for various process conditions. The acid loss reaction was introduced in Fick's law, and the calculation showed a good agreement with experimental results. In order to obtain good profile patterns with sufficient controllability, the distribution of acids in the resist must be controlled as well as diffusion length. The resist patterns replicated using X-ray lithography corresponded to those expected from experimental results.