Process conditions for the fabrication of subwavelength-scale structures by x-ray lithography in PMMA films

Sven C. Achenbach; Timo Mappes; Rainer Fettig; Jeanine Kando; Juergen Mohr

doi:10.1117/12.546030

15 September 2004 Process conditions for the fabrication of subwavelength scale structures by x-ray lithography in PMMA films

Sven C. Achenbach, Timo Mappes, Rainer Fettig, Jeanine Kando, Juergen Mohr

Author Affiliations +

Proceedings Volume 5450, Photonic Crystal Materials and Nanostructures; (2004) https://doi.org/10.1117/12.546030
Event: Photonics Europe, 2004, Strasbourg, France

Abstract

Periodically structured dielectric media with lattices on a sub-wavelength scale are receiving increased attention as they enable a variety of photonics applications. Fabrication, however, still imposes challenges to the scientific community. This article discusses process modifications in deep X-ray lithography to reduce minimum feature size and eventually allow the fabrication of high aspect ratio photonic crystal slabs with a moderate refractive index. Proximity printing requires an X-ray mask with high contrast and lateral resolution. Electron beam writing exposure doses were optimized to pattern feature sizes down to 400 nm in 3 μm thick resist. The voids were subsequently electroformed with 2 μm gold to generate the absorbers on a suspended silicon nitride membrane. The mask was copied into PMMA films of 5 μm thickness using X-ray lithography at about 0.4 nm. The yield of free standing smallest features is limited by adhesion of the resist to the substrate. Structures with aspect ratios as high as 8 to 12 tend to collapse after dip development. Periodic features are increased on the order of tens of nanometers compared to mask absorbers. Lattice constants need to be slightly reduced at fixed pore diameters before first photonic demonstrators made of PMMA can be fabricated.

Citation Download Citation

Sven C. Achenbach, Timo Mappes, Rainer Fettig, Jeanine Kando, and Juergen Mohr "Process conditions for the fabrication of subwavelength scale structures by x-ray lithography in PMMA films", Proc. SPIE 5450, Photonic Crystal Materials and Nanostructures, (15 September 2004); https://doi.org/10.1117/12.546030

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