Nanofabrication advances for high efficiency critical-angle transmission gratings

Alexander R. Bruccoleri; Dong Guan; Ralf K. Heilmann; Steve Vargo; Frank DiPiazza; Mark L. Schattenburg

doi:10.1117/12.2024357

26 September 2013 Nanofabrication advances for high efficiency critical-angle transmission gratings

Alexander R. Bruccoleri, Dong Guan, Ralf K. Heilmann, Steve Vargo, Frank DiPiazza, Mark L. Schattenburg

Proceedings Volume 8861, Optics for EUV, X-Ray, and Gamma-Ray Astronomy VI; 886119 (2013) https://doi.org/10.1117/12.2024357
Event: SPIE Optical Engineering + Applications, 2013, San Diego, California, United States

Abstract

We report several break-through nanofabrication developments enabling high efficiency and high resolving power spectrometers in the soft x-ray band. The device is the critical-angle transmission (CAT) grating, which combines the low mass and relaxed alignment tolerances of a transmission grating with the high broad-band efficiency and high diffraction orders of a blazed reflection grating. Past work successfully demonstrated the CAT grating concept; however, the open-area fraction was often less than 20% whilst more than 50% is desired. This presents numerous nanofabrication challenges including a requirement for a freestanding silicon membrane of ultra high-aspect ratio bars at a period of 200 nanometers with minimal cross support blockage. Furthermore, the sidewalls must be smooth to a few nanometers to efficiently reflect soft x-rays. We have developed a complete nanofabrication process for creating freestanding CAT gratings via plasma-etching silicon wafers with a buried layer of SiO₂. This removable buried layer enables combining a record-performance plasma etch for the CAT grating with a millimeter-scale honeycomb structural support to create a large-area freestanding membrane. We have also developed a process for polishing sidewalls of plasma-etched ultra-high aspect ratio nanoscale silicon structures via potassium hydroxide (KOH). This process utilizes the anisotropic etch nature of single crystal silicon in KOH. We developed a novel alignment technique to align the CAT grating bars to the {111} planes of silicon within 0.2 degrees, which enables KOH to etch away sidewall roughness without destroying the structure, since the {111} planes etch approximately 100 times slower than the non-{111} planes. Preliminary results of a combined freestanding grating with polishing are presented to enable efficient diffraction of soft x-rays.

Citation Download Citation

Alexander R. Bruccoleri, Dong Guan, Ralf K. Heilmann, Steve Vargo, Frank DiPiazza, and Mark L. Schattenburg "Nanofabrication advances for high efficiency critical-angle transmission gratings", Proc. SPIE 8861, Optics for EUV, X-Ray, and Gamma-Ray Astronomy VI, 886119 (26 September 2013); https://doi.org/10.1117/12.2024357

ACCESS THE FULL ARTICLE

INSTITUTIONAL
Select your institution to access the SPIE Digital Library.

SELECT YOUR INSTITUTION

PERSONAL
Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.

PERSONAL SIGN IN

No SPIE Account? Create one

PURCHASE THIS CONTENT

SUBSCRIBE TO DIGITAL LIBRARY

50 downloads per 1-year subscription

Members: $195

Non-members: $335 ADD TO CART

25 downloads per 1 - year subscription

Members: $145

Non-members: $250 ADD TO CART

PURCHASE SINGLE ARTICLE

Includes PDF, HTML & Video, when available