Abstract
We report an extension of plasmonic lithography to nanoscale 2.5-dimensional (2.5D) surface patterning. To obtain the impulse response of a plasmonic lithography system, we described the field distribution of a point dipole source generated by a metallic ridge aperture with a theoretical model using the concepts of quasi-spherical waves and surface plasmon–polaritons. We performed deconvolution to construct an exposure map of a target shape for patterning. For practical applications, we fabricated several nanoscale and microscale structures, such as a cone, microlens array, nanoneedle, and a multiscale structure using the plasmonic lithography system. We verified the possibility of applying plasmonic lithography to multiscale structuring from a few tens of nanometres to a few micrometres in the lateral dimension. We obtained a root-mean-square error of 4.7 nm between the target shape and the patterned shape, and a surface roughness of 11.5 nm.
Highlights
The development of three-dimensional (3D) micro- and nanofabrication has attracted a lot of attention because of its relevance to various fields[1,2,3,4,5,6]
In order to extend the scope of plasmonic lithography to nanoscale 2.5D surface patterning, we need an exact understanding of the distribution of the electromagnetic field emitted from the aperture in terms of surface waves and space waves
Surface waves from the point source and localised surface plasmon (LSP) are composed of surface plasmon–polaritons (SPPs) and QSWs, and the field intensity distribution of light transmitted through a bowtie aperture have been successfully described in analytical form on the basis of SPPs and QSWs25
Summary
Description of impulse response of plasmonic lithography system. As light is illuminated on a bowtie aperture, the LSPs resulting from interaction at the metallo-dielectric interface and transmitted field through the aperture generate field distributions around the aperture. Because the PSF modelling is experimentally calibrated with the geometrical dimensions of the dose-modulated spot patterns recorded on the PR, the effects of PR bleaching, change in absorptivity with light exposure, could be suppressed, which yields little disparity between the simulated shape and the patterning results. In order to demonstrate that the patterning results are in good agreement with the target shape, we fabricated a cone-shaped pattern by using an exposure map generated by the deconvolution algorithm (Fig. 3a). By setting the simulated spot shape as an impulse response of the plasmonic lithography system, we performed deconvolution on the spot pattern to obtain an exposure map that consists of the exposure location and exposure time. We expect the surface patterning with plasmonic lithography to facilitate fabrication of nanoscale and microscale devices
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