Projecting high depth-to-width aspect ratio of nanolithography with a four-layer metallic waveguide structure

Abstract

The depth-to-width aspect ratio of pattern engineering by surface plasmons is limited for its field intensity exponential attenuation property. We here report a method to enhance patterns' aspect ratio with a maskphotoresist-dielectric-metal four-layer metallic waveguide structure. The parameters, index and thickness, of the dielectric layer are discussed and analyzed to illustrate their affection to the patterns' resolution and aspect ratio. A small thickness of dielectric with its index higher than photoresist will enhance the resolution and aspect ratio of pattern by these proposed structures. Numerical simulation results show that 40 nm half-pitch and 100 nm depth patterns could be performed by a chromium mask with period of 160 nm at the wavelength of 365 nm.High quality of nanoscale patterns is gradually important for the nanoscale science and technology nowadays, especially for the semiconductor device fabrication, integrated circuit, etc. The resolution, as one important factor of high-quality patterns, is fundamentally limited by the physics of diffraction for the traditional optical lithography which is a powerful technique for high-resolution patterning, low-cost and mass-fabrication. Over the past decade, plasmonic lithography [1-16] was available to achieve high resolution beyond the diffraction limit for broadband illuminations for imaging and interference lithography, with the aid of waveguide structure [1-3], superlens [4][5][6][7], plasmonics [8][9][10][11], metamaterials [12,13], surface plasmon generator [14-16], etc. These approaches are all based on the surface plasmons (SPs) for its wavelength is much smaller than that of light in free space at the same frequency [17].