Functionalized Ag Nanoparticles Embedded in Polymer Resists for High-Resolution Lithography

Extending the resolution limit of next-generation lithography down to 15 nm or below requires the resist to attain small features, high irradiation sensitivity, and low line edge/width roughness. To meet this prerequisite, an increase of irradiation absorption in resists is an important strategy. A negative tone, deep ultraviolet, electron beam, and helium ion beam active resist formulation has been realized comprising a hydroxystyrene-based polymer tert-butyl 2-ethyl-6-(4-hydroxyphenyl)-4-phenylheptanoate (Terpolymer). Further, the resist performance was enhanced by doping of a microemulsion-based Ag nanoparticle (size distribution ∼2 nm) irradiation sensitizer. As a result, a tenfold decrease in the critical dose (Eo) was observed by increasing Ag nanoparticle contents from 0.1 to 1.0 wt %. The developed resist patterns exhibit significantly higher sensitivities and resolutions of 50 and 34.12 μC/cm2 and ∼12 and ∼11 nm line patterns, respectively, for e-beam (Ee) and helium ion beam (EHe) irradiations. The line edge/width roughness of well-developed e-beam exposed patterns was found to be 1.5 ± 0.1/2.8 ± 0.3 nm, respectively. These e-beam/resist interactions were modeled by the Monte-Carlo trajectory, and the results were in line with the experimentally observed one. These simulations suggest the enhanced irradiation absorption inside the resist matrix with the addition of a high-electron-density Ag entity. These investigations reveal that one of the best ways to simultaneously improve the sensitivity and resolution of the resist is the optimum incorporation of higher-atomic-number nanoparticles in the polymeric matrix, which enhances the absorption cross section (σ) without altering the resist properties.