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Defining Chi for Block Copolymer Lithography



Whitney Loo, Hongbo Feng, Thomas Ferron, Ricardo Ruiz, Daniel Sunday, Paul Nealey


Block copolymer lithography, such as directed self-assembly, requires the design of nanostructured block copolymers with precise values of segregation strength, 20≤χN≤25, in order to balance covarying material properties and meet manufacturing requirements. Therefore, reliable methods of experimentally measuring the Flory-Huggins interaction parameter, χ, are needed in the intermediate segregation strength regime for systems without accessible order-disorder transition temperatures. We calculate χ_eff using strong segregation theory (SST), but due to discrepancies in L_0 from bulk versus thin film experiments, values of χ_eff using SST for were quantitatively inconsistent. Therefore, we propose to use the extent of mixing, quantified as a normalized interface width, w_m/L_0 where w_m is the interfacial width and L_0 is the block copolymer pitch, as a thermodynamic parameter. We experimentally measure w_m and L_0 for a series of lamellar A-b-(B-r-C) copolymers via resonant soft X-ray reflectivity to extract values of χ_eff N based on previous data collected for A-b-B copolymers. The extracted χ_eff values from comparisons of w_m/L_0 between the A-b-(B-r-C) copolymers and previous data on A-b-B copolymers agreed quantitatively between copolymers of different molecular weights. Block copolymers for lithographic applications are uniquely poised to use effect of mixing as a fundamental thermodynamic parameter due to their inaccessible order-disorder transition temperatures, intermediate values of χN, and the importance of w_m for line edge roughness metrics.
ACS Macro Letters


Lithography, Polymer, Block Copolymer, Reflectivity, X-ray


Loo, W. , Feng, H. , Ferron, T. , Ruiz, R. , Sunday, D. and Nealey, P. (2023), Defining Chi for Block Copolymer Lithography, ACS Macro Letters, [online], (Accessed July 16, 2024)


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Created January 11, 2023, Updated February 1, 2023