Mass-productive fabrication of a metal–insulator–metal plasmon waveguide with a linear taper for nanofocusing

Abstract

The fabrication of a metal–insulator–metal plasmon waveguide with a linear taper is reported. Highly efficient nanofocusing of light with a Au–SiO₂–Au waveguide with a three-dimensional taper had been demonstrated. However, conventional vertical taper structures were fabricated with a low-throughput process based on electron beam scanning. We propose an efficient, mass-productive fabrication process using a standard dry etching technique. A key improvement is the employment of a mixed gas of CHF₃ and O₂. By optimizing the gas composition and the cooling process of the substrate, a SiO₂ vertical taper with an angle of 19°, which is very close to the optimum 20°, was successfully produced. At the tip section, an ultra-thin waveguide as thin as 5.6 nm, only one-third of the conventional demonstration, is reproducibly realized by the employment of an atomic layer deposition of Al₂O₃. Coupling efficiency as high as 72 % numerically demonstrated.