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5 April 2013 PS-b-PHOST as a high χ block copolymers for directed self assembly: optimization of underlayer and solvent anneal processes
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Directed self-assembly (DSA) of block copolymers (BCP) could enable high resolution patterning beyond the capabilities of current optical lithography methods via pitch multiplication from lower resolution primary lithographic patterns. For example, DSA could enable dense feature production with pitches less than 80 nm from patterns generated using 193 nm exposure tools without the need for double patterning or other schemes. According to theory, microphase separation of diblock copolymers occurs when the critical condition that χN>10.5 is met while the pitch of the resulting polymer features scale as ~N2/3, where χ is the Flory Huggins interaction parameter and N is the total degree of polymerization for the diblock copolymer. In order to generate patterns with smaller pitches, N must be decreased while maintaining a χN>10.5 to allow for phase separation. This requires utilization of polymers with higher χ values as N is decreased. Current materials, such as PS-b-PMMA, exhibit a relatively low χ value of ~0.04, which limits the practical pitch of DSA line-space patterns produced using PS-b-PMMA to approximately 20 nm. In this paper, we investigate alternative materials, namely poly(styrene)-b-poly(hydroxystyrene) (PS-b-PHOST), which exhibits a high χ value via hydrogen bonding interactions that can allow for production of sub-20nm pitch DSA patterns. In order to utilize any diblock copolymer for DSA, a neutral underlayer and a method for annealing the block copolymer are required. Here, a random copolymer, poly(styrene-co-hydroxystyrene-co-glycidyl methacrylate), is developed and reported for use as a neutral underlayer for PS-b-PHOST. Furthermore, a solvent annealing method for PS-b-PHOST is developed and optimized using ethyl acetate to allow for uniform microphase separation of PS-b-PHOST.
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Nathan D. Jarnagin, Wei-Ming Yeh, Jing Cheng, Andrew Peters, Richard A. Lawson, Laren M. Tolbert, and Clifford L. Henderson "PS-b-PHOST as a high χ block copolymers for directed self assembly: optimization of underlayer and solvent anneal processes", Proc. SPIE 8680, Alternative Lithographic Technologies V, 86801X (5 April 2013);

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