Co and terpolymer reactivity ratios of chemically amplified resists

Publication date: 2 June 2017
Source:Polymer, Volume 118
Author(s): Narahari S. Pujari, Mingxing Wang, Kenneth E. Gonsalves
Resists are important multicomponent system require in microelectronic industry for fabrication of integrated circuit (IC) devices. The current high end IC (integrated circuit) technology node in manufacturing is 20 nm and looking toward 16 and 10 nm nodes to fulfil market demand. A series of chemically amplified resists (CARs) based on co and terpolymers of 4-hydroxystyrene (HOST), 2-ethyl-2-adamantyl methacrylate (EAMA) and/or a monomer-bound anionic photoacid generator (PAG) were prepared and characterized. Specifically, Triphenylsulfonium salt 4-(methacryloxy)-2,3,5,6-tetrafluorobenzenesulfonate (F4 PAG) was incorporated into the main chain to get PAG bound polymer microstructure.The aim of the study was to investigate interplay of individual monomers in co and terpolymer systems. This was achieved by understanding the reactivity ratios and monomer sequence distribution in the polymer. Analysis was conducted by using a software PROCOP version2.3. The co/terpolymer compositions were determined by quantitative ¹H NMR spectra. The copolymer reactivity ratio of each monomer was determined with Fineman–Ross, Kelen–Tüdös, and nonlinear least-squares curve- fitting methods. It was observed that EAMA is not polymerizable under given reaction conditions and copolymerization of EAMA-PAG was also not possible. HOST-EAMA system yielded reactivity ratios near zero indicating that they form quasi alternating structures. HOST-PAG system yielded copolymers rich in PAG. On the basis of the reactivity ratios determined from the binary copolymers, Alfrey–Goldfinger equations were used to estimate the compositions of the terpolymers. In terpolymer system, where two monomers were non homopolymerizable, both PAG and EAMA competed to add up to the HOST radical. All six reactivity values were less then unity indicating preferred cross propagation of radicals. PAG was the most reactive monomer. Monomer sequence distribution of copolymer and terpolymer was established to get an idea of detailed microstructure of the chain. Copolymers confirmed 84% of dyads formation of each monomer while terpolymer analysis revealed dominance of HOST centered triads. In addition to this, kinetics of terpolymerization reaction was performed to validate the theory. Findings from the study can be used to tailor make CAR synthesis for optimum EUV (extreme ultraviolet) lithography performance.

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