Plasmonic dipole nanoantennas on a SiO2/Si substrate and their characterization undefined

In this paper, the results of the successful fabrication as well as the optical backscattering characterization of single plasmonic gold dipole nanoantennas on a SiO2/Si layered substrate are shown. The nanoantennas were designed for a scattering resonance in the NIR range. In contrast to usually used glass substrates, a six inch Siwafer with a thermally oxidized SiO2 layer in combination with an electron beam lithography lift-off fabrication process has been used for the sake of compatibility with microelectronics fabrication processes. In order to achieve high structural resolutions, a bilayer resist system with different exposure sensitivities was realized. In a second step, the entire resist thickness of 540 nm was reduced to 150 nm in a single layer. The SiO2 thickness was chosen in a way that the optical near-field interactions of the nanoantennas with the silicon substrate are decoupled. The SEM characterization of the fabricated structures shows precise nanoantenna geometries with low edge roughness in the case of the bilayer resist system. The aspect ratio of the fabricated nanoantenna structures is slightly decreased compared to the desired value of five. Depending on the applied e-beam exposure dose, an increase of the structural cross-section, i.e. critical dimension of the dipole width, was observed. Furthermore, the single resist layer introduces some structuring issues. The spectral behavior of the nanoantenna structures was investigated with an optical confocal broadband backscattering measurement setup allowing the spectral characterization of single nanoantenna structures. The developed numerical models helped to understand the impact of the manufacturing imperfections providing improved designs