It is anticipated that future microlithography will require the high radiation sensitivity offered by chemically amplified (CA) resists accompanied by improved spatial resolution. In CA resists, irradiation produces a small amount of a strong Bronsted acid in the film, which then serves as a catalyst in a subsequent deprotection reaction of the polymer that modifies the film solubility. Any blurring of the image during post-exposure processing, for example by diffusion of the photogenerated acid catalyst, adversely affects image fidelity and resolution.

We have described a two-step experimental protocol that provides an unambiguous quantitative measure of image blur during post-exposure processing of CA resist films. In the first step, a CA resist film is exhaustively exposed to DUV light at a wavelength where the film is largely transparent, producing a uniform distribution of photogenerated acid in the film. The film is then heated in an infrared spectrometer and the chemical kinetics of deprotection are recorded. The second step is similar, except in this instance a different exposure wavelength is employed - one at which the resist film is much more opaque. A non-uniform distribution of photogenerated acid results and now the overall rate of deprotection is controlled both by the chemical kinetics of deprotection, and by gradient-driven diffusion of the acid catalyst from zones of high concentration to zones of low concentration. Modeling of these experimental results with kinetics simulation provides values for the magnitude of the diffusion of photogenerated acid but also yields mechanistic information that offers insight into the origins of image blur.