Lithographic feature size requirements have approached a few radius of gyration of chemically-amplified photoresist polymers used in thin film patterning. Further, the feature dimensions are commensurate with the photoacid diffusion length that defines the underlying latent image. The spatial extent of the photoacid catalyzed reaction diffusion front was characterized by neutron reflectivity for isomer-purified deuterium labeled tert-butoxycarbonyloxy calixresorcinarene molecular resists that provide a smaller building block for next-generation lithography. The spatial extent of the reaction front exceeds the size of the molecular resist with an effective diffusion constant of (0.13 ± 0.06) nm2/s determined experimentally. Within a mean field reaction-diffusion model, a photoacid trapping process was necessary to place bounds on the spatial extent and reaction extent via a reaction-limited mechanism. Further, even under ideal step-exposure conditions, surface roughness was observed after either positive or negative-tone development. However, negative tone development follows a surface restructuring mechanism, rather than etch-like dissolution in positive-tone.
Citation: Advanced Functional Materials
Pub Type: Journals
reaction-diffusion, photoresist, neutron reflectivity, roughness, polymer, lithography