Super-smooth x-ray reflection grating fabrication
作者:
A. E. Franke,
M. L. Schattenburg,
E. M. Gullikson,
J. Cottam,
S. M. Kahn,
A. Rasmussen,
期刊:
Journal of Vacuum Science&Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena
(AIP Available online 1997)
卷期:
Volume 15,
issue 6
页码: 2940-2945
ISSN:1071-1023
年代: 1997
DOI:10.1116/1.589759
出版商: American Vacuum Society
关键词: X-RAY SPECTROMETERS;DIFFRACTION GRATINGS;REFLECTION;CHROMIUM;GOLD;COMPUTERIZED SIMULATION;FABRICATION
数据来源: AIP
摘要:
Blazed, grazing incidence x-ray reflection gratings are an important component of modern high resolution spectrometers and related x-ray optics. These have traditionally been fabricated by diamond scribing in a ruling engine, or more recently by interferometric lithography followed by ion etching. These traditional methods result in gratings which suffer from a number of deficiencies, including high surface roughness and poor control of the groove profile. These deficiencies lead to poor diffraction efficiency and high levels of scattered light. We have developed a novel fabrication method for fabricating blazed x-ray reflection gratings which utilizes silicon wafers that are cut 0.7° off of the (111) plane. In solutions such as potassium hydroxide (KOH), silicon is etched in 〈111〉 directions orders of magnitude slower than in other directions, resulting in extremely smooth {111} facets. The gratings are patterned using interferometric lithography with 351.1 nm wavelength and transferred into the substrate using tri-level resist processing, reactive-ion etching (RIE), and silicon nitride masking during the KOH etch. The narrow(<0.1 μm)ridge of silicon which supports the nitride mask is removed using a chromium lift-off step followed by aCF4RIE trench etch. The result is a grating with extremely smooth blaze facets which is suitable for x-ray reflection after evaporative coating with thin Cr/Au. Atomic force microscope images confirm that fabricated gratings have less than a 0.4 nm rms roughness—much smoother than conventional gratings which have over∼1 nmroughness. Theory predicts that reduced blaze facet roughness increases diffraction efficiency. Experiments and simulations performed at the Lawrence Berkeley Laboratory and Columbia University confirm that efficiency is increased; in fact, measured peak efficiencies reach∼80%of calculated theoretical limits. Peak grating efficiencies were achieved that are∼35%greater than that of the best available ruled masters of comparable design.
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