Fundamental studies of interactions between polymer substrate and precursor in sequential infiltration synthesis

Abstract

Sequential infiltration synthesis (SIS) is becoming an important tool for resist hardening and formation of unique nanostructures. SIS is a variant of atomic layer deposition (ALD), in which the organometallic precursors are allowed to diffuse into the polymeric substrate before condensation. In contrast to ALD, the extended diffusion time in SIS potentially allows for extensive penetration into the substrate. An important parameter in SIS is the affinity of the precursor with the polymer substrate. Differences in affinity can be exploited, for e.g., for generation of patterned structures within block copolymers. To date, the interactions between the precursor molecules, for example trimethyl aluminium (TMA) have been inferred from in situ or ex situ vibrational spectroscopy. Potentially much richer information can be gained from NMR and transmission FTIR spectroscopy of solutions of precursor and polymer. Fundamental studies of PMMA and TMA allow identification and screening of novel polymer substrates for SIS. Previous studies have provided broad design rules for SIS; e.g., highly-polar and strongly basic structures enhance uptake of precursors. The precursor molecules such as TMA are Lewis acids and hence will associate with functional groups having base character. We have investigated SIS polymers that incorporate a stronger Lewis base group, sulfinyl, in poly((2-methylsulfinyl) ethyl methacrylate) (PMSEMA). Details of the interactions between TMA and PMSEMA in solution, and as films, and comparison with a range of other materials, provide information on potential of these materials for SIS.