Thin films of lamellar poly(styrene-b-methyl methacrylate) (PS-PMMA) block copolymers were prepared on brushed
silicon substrates with a range of thicknesses. The brushes are expected to eliminate preferential interactions at the
substrate, thereby enabling perpendicular domain orientations relative to the interfaces. Using a combination of surface
microscopy and grazing incidence small-angle X-ray scattering, we demonstrate that i) the brushed substrates are weakly
preferential to PMMA; and ii) the average lamellar domain orientation is perpendicular to the substrate, but some
domains are mis-oriented by up to 40º. We propose that PMMA domains deform to increase their contact area at the
slightly preferential substrate, and this behavior drives the formation of out-of-plane defects such as bent or tilted
domains. These outcomes suggest that depth-resolved measurements are needed to fully optimize materials and
processes for block copolymer lithography.
The acid-catalyzed deprotection of glassy poly(4-hydroxystyrene-co-tertbutyl acrylate) films was studied with infrared absorbance spectroscopy and stochastic simulations. Experimental data were interpreted with a simple description of subdiffusive acid transport coupled to second-order acid loss. This model predicts key attributes of observed deprotection rates, such as fast reaction at short times, slow reaction at long times, and a nonlinear dependence on acid loading. Fickian diffusion is approached by increasing the postexposure bake temperature or adding plasticizing agents to the polymer resin. These findings demonstrate that acid mobility and overall deprotection kinetics are coupled to glassy matrix dynamics. To complement the analysis of bulk kinetics, acid diffusion lengths were calculated from the anomalous transport model and compared with nanopattern line widths. The consistent scaling between experiments and simulations suggests that the anomalous diffusion model could be further developed into a predictive lithography tool.
The acid-catalyzed deprotection of glassy poly(4-hydroxystyrene-co-tert butyl acrylate) films was studied with infrared absorbance spectroscopy and stochastic simulations. Experimental data were interpreted with a simple description of subdiffusive acid transport coupled to second-order acid loss. This model predicts key attributes of observed deprotection rates, such as fast reaction at short times, slow reaction at long times, and a non-linear dependence on acid loading. The degree of anomalous character is reduced by increasing the post-exposure bake temperature or adding plasticizing agents to the polymer resin. These findings indicate that the acid mobility and overall deprotection kinetics are coupled to glassy matrix dynamics. Furthermore, the acid diffusion lengths were calculated from the anomalous transport model and compared with nanopattern line widths. The consistent scaling between experiments and simulations suggests that the anomalous diffusion model could be further developed into a predictive lithography tool.
We report on the development of a new measurement method, resonant critical-dimension small-angle x-ray scattering (res-CDSAXS), for the characterization of the buried structure of block copolymers (BCP) used in directed self assembly (DSA). We use resonant scattering at the carbon edge to enhance the contrast between the two polymer blocks and allow the determination of the three-dimensional shape of the native lamella in a line–space pattern by CDSAXS. We demonstrate the method by comparing the results from conventional CDSAXS to res-CDSAXS on a 1:1 DSA BCP sample with a nominal 50-nm pitch. The res-CDSAXS method provides substantially improved uncertainty in the fit of the line shape and allows the determination of the buried structure.
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