Study of Fluorine-Containing Block Copolymers Designed for Top-Down and Bottom-Up Lithography

A new series of fluorine-containing block copolymers of poly(styrene-block-2,2,2-trifluoroethyl methacrylate) (PS-b-PTFEMA) and poly[styrene-block-(methyl methacrylate-co-2,2,2-trifluoroethyl methacrylate)] (PS-b-(PMMA-co-PTFEMA)), which can be used for both top-down and bottom-up lithography, were developed. Integrated patterns such as “dots in lines” were successfully obtained through combination of degradation of the fluorine-containing block by e-beam exposure and lateral ordering of the crosslinked PS block’s self-assembly. Lateral ordering of arrays of dots was observed in thin films of PS-b-PTFEMS in which PS was the minor block, and in thin films of PS-b-(PMMA-co-PTFEMA) in which polystyrene (PS) was the major block. These thin films were then exposed as in conventional e-beam and deep-UV lithography to generate integrated patterns. Summary of Research: As semiconductor patterning reaches smaller length scales (now below 50 nm), there arises a need for new and innovative strategies for structure formation. Rather than relying solely on expensive tools to drive down resolution, we have decided to use the natural process of block copolymer self­assembly to achieve this goal. Block copolymers are two or more polymers linked at one end by a covalent bond. A combination of entropic and enthalpic effects drives the polymers to form periodic nanostructures such as spheres, cylinders and lamellae depending on the relative volume fraction of each polymer block. The molecular weight of the polymer determines the length scale of the dimensions and allows control of the domain spacing of the structures. A smaller domain spacing and higher degree of lateral ordering are achieved by incorporating polymers with high immiscibility (i.e., large χ value). By incorporating a negative­tone photoresist capability into one of the blocks, and choosing the other polymer block so that it is selectively removable, we can form integrated nano­structured templates that can be used for various applications. Currently, several different platforms for exploring block copolymer self­assembly are being investigated, however, there remains relatively few block copolymers with large χ Figure 1: The chemical structures of PS-bPTFEMA and PS-b-(PMMA-co-PTFEMA). values applicable to both conventional top­down lithography and bottom­up lithography. In this study, we present a novel strategy: a polymer which is both degradable and highly immiscible with PS is introduced into a PS­containing block copolymer. The polymer 2,2,2-trifluoroethyl methacrylate (PTFEMA) (a positive­tone resist) or poly(methyl methacrylate­co­2,2,2­ trifluoroethyl methacrylate) (PMMA-co­PTFEMA) are