Degradation in image contrast becomes a concern at higher numerical apertures (NA) due to mask induced polarization effects. Rigorous coupled-wave analysis (RCWA) was used to simulate the polarization of radiation by the photomask. The results show that higher NA leads to greater polarization effects in all cases. In general, materials with higher refractive indices and lower extinction coefficients tend to pass more of the TM polarization state, whereas materials with lower refractive indices and a relatively wider range of extinction coefficients pass more TE polarized radiation. These properties can provide new design considerations for the development of next generation masking materials.
The unique properties of metamaterials, namely their negative refractive index, permittivity, and permeability, have gained much recent attention. Research into these materials has led to the realization of a host of applications that may be useful to enhance optical nanolithography, such as a high pass pupil filter based on an induced transmission filter design, or an optical superlens. A large selection of materials has been examined both experimentally and theoretically through wavelength to verify their support of surface plasmons, or lack thereof, in the DUV spectrum via the attenuated total reflection (ATR) method using the Kretschmann configuration.
At DUV wavelengths, materials that were previously useful at mid-UV and longer wavelengths no longer act as metamaterials. Composites bound between metallic aluminum and Al2O3 exhibit metamaterial behavior, as do other materials such as tin and indium. This provides for real opportunities to explore the potential of the use of such materials for image enhancement with easily obtainable materials at desirable lithographic wavelengths.
A software program was created to evaluate possible metal-insulator material stack combinations to find materials with a suitable surface plasmon dispersion for the DUV. The resulting materials are a comprised of a multilayer Al-Al2O3-Al stack as well as a simple Al-photoresist stack.
These stacks were then fabricated, and used to image the surface plasmons generated by this metamaterial using plasmonic interference lithography, a technique very similar to 2-beam interference lithography used frequently in the Nanolithography Research Labs, with resolution down to an 80nm period.
Library of Congress Subject Headings
Metamaterials; Nanolithography; Plasmons (Physics); Polarization (Light); Masks (Electronics)
Microsystems Engineering (Ph.D.)
Department, Program, or Center
Microsystems Engineering (KGCOE)
Bruce W. Smith
Estroff, Andrew Charles, "Plasmonic Materials For Use In Alternative Approaches To DUV Nanolithography" (2014). Thesis. Rochester Institute of Technology. Accessed from
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