title: Neutron reflectivity characterization of the photoacid reaction-diffusion latent and developed images of molecular resists for extreme ultraviolet lithography.
abstract: Lithographic feature size requirements have approached a few radius of gyration of photoresist polymers used in thin-film patterning. Furthermore, the feature dimensions are commensurate with the photoacid diffusion length that defines the underlying latent image. Smaller imaging building blocks may enable reduced feature sizes; however, resolution limits are also dependent upon the spatial extent of the photoacid-catalyzed reaction diffusion front and subsequent dissolution mechanism. The reaction-diffusion front was characterized by neutron reflectivity for ccc stereoisomer-purified, deuterium-labeled tert-butoxycarbonyloxy calix[4]resorcinarene molecular resists. The spatial extent of the reaction front exceeds the size of the molecular resist with an effective diffusion constant of (0.13 ± 0.06) nm(2)/s for reaction times longer than 60 s, with the maximum at shorter times. Comparison to a mean-field reaction-diffusion model shows that a photoacid trapping process provides bounds to the spatial and extent of reaction via a reaction-limited mechanism whereas the ratio of the reaction rate to trapping rate constants recovers the effective diffusion peak. Under the 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 development.
authors.affiliation: Polymers Division, National Institute of Standards & Technology, Gaithersburg, Maryland 20899, USA. vprabhu@nist.gov
authors.forename: Vivek M
authors.initials: VM
authors.lastname: Prabhu
authors.forename: Shuhui
authors.initials: S
authors.lastname: Kang
authors.forename: Jing
authors.initials: J
authors.lastname: Sha
authors.forename: Peter V
authors.initials: PV
authors.lastname: Bonnesen
authors.forename: Sushil
authors.initials: S
authors.lastname: Satija
authors.forename: Wen-li
authors.initials: WL
authors.lastname: Wu
authors.forename: Christopher K
authors.initials: CK
authors.lastname: Ober