INSTITUTE OF APPLIED PHYSICS - Wire grid polarizer for deep and vacuum ultra violet applications
URL: http://www.iap.uni-jena.de/Micro_+structure+Technology/Research/Micro_+_Nanooptics/Wire+grid+polarizer+for+deep+and+vacuum+ultra+violet+applications.print
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Wire grid polarizer for deep and vacuum ultra violet applications

The polarization state is an inherent property of light. Nowadays, many optical instruments such as spectrometers, ellipsometers or lithography tools require a profound control over the polarization state. This can be accomplished by wire gird polarizers, which offer large angle of incidence ranges, large areas and large spectral application ranges from the UV to FIR and may be integrated with other optical elements such as photomasks. In order to benefit from better resolution and material specific electronic transitions the application wavelength of next generation optical equipment strives further into the DUV and VUV where wire grid polarizers are not yet available. Our aim is to overcome this hindrance and provide technological and scientific solutions in order to path the way for real world applications of wire grid polarizer in the wavelength range from 150 nm to the FIR.
Wire grid polarizers are form birefringent grating elements where light with an electric field vector parallel to the ridges is strongly absorbed or reflected while the orthogonal component is transmitted. In order to avoid diffraction, the period must be much smaller than the wavelength, we achieved this by a self-aligned double patterning process. Although the involved processes are carefully adjusted systematical deviations of the geometry (see Figure 1), such facets at the top of the ridges or line edge roughness cannot be avoided. From rigorous simulations of the optical performance it is well known that even sub nanometer deviations can lead to inacceptable deterioration of the optical performance. To counter act this, we are developing in situ and ex situ measurements techniques to facilitate a tight process control. Beside the geometrical prerequisites, suitable materials must be utilized. While the currently used metals such as aluminum fail in the DUV and VUV, we demonstrated that materials with direct electronic transitions such as wide band gap semiconductors can be used. Figure 1 depicts the application ranges of several materials.

WGP_VUV_01   WGP_VUV_02
Figure 1: Application wavelength ranges of different materials for wire grid polarizer [1] and cross section of a wire grid polarizer.
(rights: IAP)


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      Limits of Wire Grid Polarizers further into the Deep Ultraviolet Spectral
      Range, Adv. Opt. Mater. 4, 1780-1786 (2016).
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      175 nm period grating fabricated by i-line proximity mask-aligner
      lithography, Opt. Lett. 42(19), (2017).
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      Fabrication influences on deep-ultraviolet tungsten wire grid polarizers
      manufactured by double patterning, Opt. Lett. 39(22), 6434-6437 (2014).
[4]  C. Stock, T. Siefke, U. Zeitner, E. Kley, Nano-optical quarter-wave plates
      for applications in the visible wavelength regime: fabrication, tolerances
      and in-situ process control, Ilmenau (September), 11-15 (2017).
[5]  T. Siefke, E.-B. Kley, A. Tünnermann, S. Kroker, Design and fabrication of
      titanium dioxide wire grid polarizer for the far ultraviolet spectral range,
      Proceedings of SPIE, 9927 (2016).
[6]  T. Siefke, S. Kroker, K. Pfeiffer, O. Puffky, K. Dietrich, D. Franta, I. Ohlídal,
      A. Szeghalmi, E.-B. Kley, A. Tünnermann, Materials Pushing the Application
      Limits of Wire Grid Polarizers further into the Deep Ultraviolet Spectral Range,
      Adv. Opt. Mater. 4(11), (2016).
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       Simulation of the influence of line edge roughness on the performance of deep
       ultraviolet wire grid polarizers, Proceedings of SPIE, 10330 (2017).
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       diffractive photo-mask for sub-500nm resolution proximity i-line mask-
       aligner lithography, Proceedings of SPIE, 9426 (2015).
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       and performance prediction of nano-optical wire grid polarizers based on
       guided mode resonances, Proceedings of SPIE, pp. 10330-31 (2017).
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       Efficient, deterministic, and large scale realization of ultra-small gaps for
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