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Besides block copolymer, gel defects in neutral layer is another concern in directed self assembly lithography. To find appropriate filtration, we studied gel reduction in neutral layer materials. The test includes coating defectivity evaluation and gel removal test using various materials of filter membrane and neutral layer materials varied in monomer proportion of the polystyrene-random-poly(methyl methacrylate) (PS-r-PMMA) copolymer. Practical results using real world fluids and filters are obtained on the basis of collaboration. As a result, for intermediate PS content materials, Nylon 6,6 5 nm filter is found to be appropriate for gel reduction based on both coating defectivity and gel removal testing results. For relatively high PS content material, both Nylon 6,6 5 nm and HDPE 2 nm are recommended also based on the results. The mechanism of the gel removal is schemed based on hydrophilic interaction between Nylon 6,6 and hydrophilic part of the polymer.

Deep submicron resist profile simulation and characterization of electron beam lithography system for cell projection and direct writing