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Journal of Micro/Nanolithography, MEMS, and MOEMS

High-resolution x-ray masks for high aspect ratio microelectromechanical systems applications
Author(s): Lin Wang; Todd R. Christenson; Yohannes M. Desta; Rainer K. Fettig; Jost Goettert
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Paper Abstract

The advanced requirements of bio-MEMS and MOEMS, i.e., low sidewall surface roughness, submicron critical dimension, and high aspect ratio, necessitate the use of an intermediate mask and a soft x-ray lithography process to fabricate working x-ray masks that are suitable for deep x-ray lithography. Intermediate masks consist of 2 to 2.5-μm gold patterns on membranes/substrates that are highly transparent to x-ray radiation, whereas working masks possess greater than 5 μm of gold patterns. In this work, 1-μm silicon nitride membranes are produced by a low pressure chemical vapor deposition (LPCVD) process on both the front and backside of <100> prime grade wafers and anisotropic wet etch through silicon nitride etch masks. E-beam lithography is used to pattern 0.8- to 3-μm-thick resist layers with submicron resolution. In the case of the 3-μm resist layers, the features are electroplated with approximately 2 μm of gold to form an intermediate mask. The 0.8-μm-thick layers are electroplated with gold up to a thickness of 0.6 µm and form initial masks, which are in turn used in a soft x-ray lithographical process to make intermediate masks. The process of building a high-resolution intermediate x-ray mask, directly by e-beam patterning a 3 μm layer of e-beam resist, followed by gold electroplating, is found to be viable but requires the use of a high energy (>100 keV) e-beam writer. The stability of the resist pattern during soft x-ray lithography (SXRL) by use of an initial mask is found to be problematic. Double-side lithography and gold electroplating, can effectively reduce the aspect ratio of the mask pattern, eliminates the problems associated with the use of an initial mask to fabricate intermediate x-ray masks.

Paper Details

Date Published: 1 July 2004
PDF: 6 pages
J. Micro/Nanolith. MEMS MOEMS 3(3) doi: 10.1117/1.1753271
Published in: Journal of Micro/Nanolithography, MEMS, and MOEMS Volume 3, Issue 3
Show Author Affiliations
Lin Wang, Louisiana State Univ. (United States)
Todd R. Christenson, Sandia National Labs. (United States)
Yohannes M. Desta, Louisiana State Univ. (United States)
Rainer K. Fettig, NASA Goddard Space Flight Ctr. (United States)
Jost Goettert, Louisiana State Univ. (United States)

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