Highly sensitive EUV photoresists remain a critical challenge to enable high volume manufacturing with EUV lithography. Chemically amplified resists continue to provide the best sensitivity for EUV photoresists, but the high EUV transparency of most resists continues to waste a large percentage of EUV photons that pass through the resist film without photochemically generating acid. Highly fluorinated polymers have been proposed as more sensitive resist materials because fluorine increases EUV absorption of a material. Thus, methacrylate-like polymers with fluorinated backbones are an attractive possibility for new EUV resist materials. Trifluoromethacrylates are known to undergo free radical polymerization with electron rich comonomers such as vinyl ethers. The resulting polymers have backbone trifluoromethyl groups that enhance the absorption of EUV photons while retaining the potential for solubility change by acid-catalyzed tertiary ester deprotection similar to methacrylate-based chemically amplified resists. Interestingly, copolymerizations of trifluoromethacrylates and vinyl ethers are not particularly sensitive to traditional experimental parameters that influence polymer molecular weight. Instead, we have found that the structure of the vinyl ether comonomer has a profound impact on polymer molecular weight with acyclic vinyl ethers generating very high molecular weight polymers (Mw exceeding 100,000 g/mol) and cyclic vinyl ethers generating very low molecular weight polymers (Mw less than 10,000 g/mol) under similar conditions. Combination of cyclic and non-cyclic vinyl ethers in the monomer feed enables the synthesis of polymers at a desired molecular weight with a narrow polydispersity (PDI less than 2). Initial EUV contrast curves demonstrate potential for highly sensitive photoresists using these backbone-fluorinated polymers. A variety of polymers have been prepared to determine optimum compositions of leaving group, sensitizing, and etch resistant monomers. Additionally, compositions with a variety of functional groups were prepared to optimize the polymer properties to enable resists that form uniform films with low unexposed film thickness loss while maintaining high EUV sensitivity. EUV lithography of one of the resist materials demonstrates its utility as a photoresist capable of printing features to about 30 nm. Continued optimization of materials is focused on resolving features below 20 nm.
Resolution, line edge roughness, sensitivity and low
outgassing are the key focus points for extreme ultraviolet (EUV) resist
materials. Sensitivity has become increasingly important so as to address
throughput concerns in device manufacturing and compensate for the
low power of EUV sources. Recent studies have shown that increasing
the polymer linear absorption absorption coefficient in EUV resists
translates to higher acid generation efficiency and good pattern
formation. In this study, novel high absorbing polymer platforms are
evaluated. The contributing effect of the novel absorbing chromophore to
the resultant chemically amplified photoresist is evaluated and compared
with a standard methacrylate PAG Bound Polymer (PBP) platform. We
report that by increasing EUV absorption, we cleanly resolved 17 nm 1:1
line space can be achieved at a sensitivity of 14.5 mJ/cm2, which is
consistent with dose requirements dictated by the ITRS roadmap. We
also probe the effect of fluorinated small molecule additives on acid
yield generation (Dil C) at EUV of a PBP platform.
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