Neutron Reflectivity Characterization of the Photoacid Reaction-Diffusion Latent and Developed Images of Molecular Resists for Extreme Ultraviolet Lithography

摘要

Lithographic feature size requirements have approached a fewnradius of gyration of photoresist polymers used in thin-film patterning.nFurthermore, the feature dimensions are commensurate with the photoacidndiffusion length that defines the underlying latent image. Smaller imagingnbuilding blocks may enable reduced feature sizes; however, resolution limits arenalso dependent upon the spatial extent of the photoacid-catalyzed reactionndiffusion front and subsequent dissolution mechanism. The reaction-diffusionnfront was characterized by neutron reflectivity for ccc stereoisomer-purified,ndeuterium-labeled tert-butoxycarbonyloxy calix[4]resorcinarene molecular resists.nThe spatial extent of the reaction front exceeds the size of the molecularnresist with an effective diffusion constant of (0.13 ± 0.06) nm2/s for reactionntimes longer than 60 s, with the maximum at shorter times. Comparison to anmean-field reaction-diffusion model shows that a photoacid trapping processnprovides bounds to the spatial and extent of reaction via a reaction-limited mechanism whereas the ratio of the reaction rate tontrapping rate constants recovers the effective diffusion peak. Under the ideal step-exposure conditions, surface roughness wasnobserved after either positive- or negative-tone development. However, negative-tone development follows a surfacerestructuringnmechanism rather than etch-like dissolution in positive-tone development.