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Fabricating Radial Groove Gratings Using Projection PhotolithographyProjection photolithography has been used as a fabrication method for radial grove gratings. Use of photolithographic method for diffraction grating fabrication represents the most significant breakthrough in grating technology in the last 60 years, since the introduction of holographic written gratings. Unlike traditional methods utilized for grating fabrication, this method has the advantage of producing complex diffractive groove contours that can be designed at pixel-by-pixel level, with pixel size currently at the level of 45 45 nm. Typical placement accuracy of the grating pixels is 10 nm over 30 nm. It is far superior to holographic, mechanically ruled or direct e-beam written gratings and results in high spatial coherence and low spectral cross-talk. Due to the smooth surface produced by reactive ion etch, such gratings have a low level of randomly scattered light. Also, due to high fidelity and good surface roughness, this method is ideally suited for fabrication of radial groove gratings. The projection mask is created using a laser writer. A single crystal silicon wafer is coated with photoresist, and then the projection mask, with its layer of photoresist, is exposed for patterning in a stepper or scanner. To develop the photoresist, the fabricator either removes the exposed areas (positive resist) of the unexposed areas (negative resist). Next, the patterned and developed photoresist silicon substrate is subjected to reactive ion etching. After this step, the substrate is cleaned. The projection mask is fabricated according to electronic design files that may be generated in GDS file format using any suitable CAD (computer-aided design) or other software program. Radial groove gratings in off-axis grazing angle of incidence mount are of special interest for x-ray spectroscopy, as they allow achieving higher spectral resolution for the same grating area and have lower alignment tolerances than traditional in-plane grating scheme. This is especially critical for NASA Constellation- X project that will utilize hundreds of gratings all of which need to be precisely aligned for x-ray observation of space.
Document ID
20090041777
Acquisition Source
Goddard Space Flight Center
Document Type
Other - NASA Tech Brief
External Source(s)
http://www.techbriefs.com/component/content/article/6364
Authors
Iazikov, Dmitri (LightSmyth Technologies, Inc. Eugene, OR, United States)
Mossberg, Thomas W. (LightSmyth Technologies, Inc. Eugene, OR, United States)
Date Acquired
August 24, 2013
Publication Date
December 1, 2009
Publication Information
Publication: NASA Tech Briefs, December 2009
Subject Category
Man/System Technology And Life Support
Report/Patent Number
GSC-15686-1
Distribution Limits
Public
Copyright
Public Use Permitted.

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IDRelationTitle20090041741Collected WorksNASA Tech Briefs, December 2009
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