Extreme Ultraviolet and Soft X-Ray Diffraction Efficiency of a Blazed Reflection Grating Fabricated by Thermally Activated Selective Topography Equilibration. (arXiv:2003.06449v1 [astro-ph.IM])
<a href="http://arxiv.org/find/astro-ph/1/au:+McCoy_J/0/1/0/all/0/1">Jake A. McCoy</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+McEntaffer_R/0/1/0/all/0/1">Randall L. McEntaffer</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Miles_D/0/1/0/all/0/1">Drew M. Miles</a>
Future observatories utilizing reflection grating spectrometers for extreme
ultraviolet (EUV) and soft X-ray (SXR) spectroscopy require high-fidelity
gratings with both blazed groove facets and custom groove layouts that are
often fanned or feature a slight curvature. While fabrication procedures
centering on wet anisotropic etching in monocrystalline silicon produce highly
efficient blazed gratings, the precision of a nonparallel groove layout is
limited by the cubic structure of the silicon crystal. This motivates the
pursuit of alternative techniques to grating manufacture, namely thermally
activated selective topography equilibration (TASTE), which uses gray-scale
electron-beam lithography to pattern multilevel structures in resist followed
by an optimized polymer thermal reflow to smooth the 3D patterns into
continuous surface relief profiles. Using TASTE, a mold for a reflection
grating with a periodicity of 400 nm and grooves resembling an asymmetric
sawtooth was patterned in 130 nm thick poly(methyl methacrylate) resist on a
silicon substrate over a 50 mm by 7.5 mm area. This structure was coated with
15 nm of gold by electron-beam physical vapor deposition using titanium as an
adhesion layer and then tested for EUV and SXR diffraction efficiency at
beamline 6.3.2 of the Advanced Light Source synchrotron facility. Results
demonstrate a quasi-blaze response characteristic of a 27 degree blaze angle
with groove facets smooth to 1.5 nm rms. Absolute peak-order efficiency ranges
from 75% to 25%, while total relative efficiency measures gap90% across the
measured bandpass of 15.5 nm > lambda > 1.55 nm.
Future observatories utilizing reflection grating spectrometers for extreme
ultraviolet (EUV) and soft X-ray (SXR) spectroscopy require high-fidelity
gratings with both blazed groove facets and custom groove layouts that are
often fanned or feature a slight curvature. While fabrication procedures
centering on wet anisotropic etching in monocrystalline silicon produce highly
efficient blazed gratings, the precision of a nonparallel groove layout is
limited by the cubic structure of the silicon crystal. This motivates the
pursuit of alternative techniques to grating manufacture, namely thermally
activated selective topography equilibration (TASTE), which uses gray-scale
electron-beam lithography to pattern multilevel structures in resist followed
by an optimized polymer thermal reflow to smooth the 3D patterns into
continuous surface relief profiles. Using TASTE, a mold for a reflection
grating with a periodicity of 400 nm and grooves resembling an asymmetric
sawtooth was patterned in 130 nm thick poly(methyl methacrylate) resist on a
silicon substrate over a 50 mm by 7.5 mm area. This structure was coated with
15 nm of gold by electron-beam physical vapor deposition using titanium as an
adhesion layer and then tested for EUV and SXR diffraction efficiency at
beamline 6.3.2 of the Advanced Light Source synchrotron facility. Results
demonstrate a quasi-blaze response characteristic of a 27 degree blaze angle
with groove facets smooth to 1.5 nm rms. Absolute peak-order efficiency ranges
from 75% to 25%, while total relative efficiency measures gap90% across the
measured bandpass of 15.5 nm > lambda > 1.55 nm.
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