Nanofabrication of plasmonic structures on insulating substrates by resist-on-metal bilayer lift-off.

In last few decades, micro- and nano-fabrication techniques based on photolithography and electron beam lithography have advanced greatly, mainly in the field of semiconductor fabrication. Such techniques are generally transferrable to the fabrication of plasmonic structures and metamaterials. However, plasmonic devices often require a transparent insulating substrate to be operational at visible or near-infrared wavelengths. Here we report a resist-on-metal bilayer lift-off technique enabling the fabrication of plasmonic structures on insulating substrates. The metal layer under the resist eliminates major difficulties in lithography, such as charging during electron beam exposure and uncontrolled diffuse optical scattering during photolithography. In addition, the resist-on-metal bilayer can be migrated to different substrates with minimal process alteration, because the material properties of the substrate, such as secondary electron emission or optical reflectance, become irrelevant due to the shielding provided by the metal layer. As demonstrations, we fabricate large-scale plasmonic waveguides and Bragg gratings, adiabatically-modulated plasmonic waveguide couplers, and plasmonic nanoantenna arrays using the resist-on-metal bilayer lift-off process. The process can also be used to define structures formed of other materials such as dielectrics.