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.

Ion Diffusion in Chemically Amplified Resists

“…A few studies have been able to measure acid diffusivity using semidirect methods. One approach detected the time required for the acid to diffuse through a polymer film of known thickness, and then used Fick’s second law to estimate the diffusivity. , Another approach employed neutron reflectivity to record the shape of the reaction front, − and then extracted the diffusivity using a model of Fickian acid transport coupled to fast deprotection and acid trapping. However, indirect methods to examine acid diffusion and acid loss are more prevalent in the literature.…”

Exceptional Light Sensitivity by Thiol–Ene Click Lithography

“…We further optimized the lithographic performance of the thiol–ene resist systems under a variety of conditions including reduced exposure doses, adjusted the monomer concentrations and ratios of alkenes to thiols, and selected the carboxyl ligand developers (e.g., acetic acid/acetone mixture) (Figure S16). The photoelectron/radical diffusion process, in contrast to photoacid diffusion, makes non-negligible contributions to the residue of unexposed areas or bridges, especially for highly sensitive free radical-type systems. ,− The deep-UV exposure results (Figure e) indicated that the residual issue was significantly improved by the addition of adequate hydroquinone (2 wt % to monomers, with all other conditions identical). After being exposed to a dose of 10 mJ cm –2 and developed in toluene for 30 s, clear 1:1 L/S dense patterns were observed.…”

Synthesis of benzyl chlorine‐free poly(4‐acetoxystyrene) via cationic polymerization followed by Friedel‐Crafts alkylation

“…Poly(4‐hydroxystyrene)s (PHOSTs) are widely used in many fields such as drug therapy agents, 1 drug delivery, 2 self‐healing materials 3,4 and photoresists 5‐7 . When PHOSTs are used as photoresists resin for KrF and EUV photolithography process, 6,7 the pattern resolution is largely limited by molecular weight distribution (MWD), 8‐11 with critical dimension of the device features extends below 22 nm. Living or quasiliving cationic polymerization (LCP or QLCP) has offered a strategy for the macromolecular design with alkyl vinyl ethers, 12 isobutene, 13 styrene and its derivatives 14‐19 .…”