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Proceedings Paper

High-contrast deep-submicron e-beam lithography process for fabricating planar waveguide optical gratings on GaAs
Author(s): Louis C. Poli; Christine A. Kondek
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Paper Abstract

Increased interest in fabricating deep submicron gratings for diffractive optics has resulted in stronger emphasis on higher performance processing techniques. Gratings with well formed line space dimensions of less than 0.3 micron are needed to fill most applications for planar waveguide gratings on GaAs. Electron beam tools of even modest beam energy have little difficulty in patterning isolated deep submicron features. However, patterns of closely spaced features with dimensions of less than 0.4 micron line and space on GaAs suffer increasingly greater contrast degradation because of the interproximity effect. Higher beam energies or enhanced contrast processing becomes necessary. Higher contrast development techniques may extract more information from the latent image and perhaps provide better process latitude, given the same electron beam pattern generation equipment that was suitable for larger size features. In this paper, MIBK and Cellosolve acetate based developers are investigated for processing areal features and grating patterns down to 0.1 micron line and space dimensions. A Leica Instruments Electron Beam Microfabrication tool EBMF 10.5 was used at 30 keV beam energy to pattern PMMA resist on host Gallium Arsenide substrates. Samples were prepared by a thorough cleaning, followed by a dehydration bake and spin coating of PMMA (496 K mw). A two part softbake regimen was performed to promote adhesion. Lithography was done with close attention given to beam current, spot size and machine calibration to insure that all samples were patterned identically. No post bake is necessary for PMMA. Latent images were then developed in different developers. MIBK based developers in dilution of 1:1, 1:2 and 1:3 with isopropyl alcohol were examined for determination of dose to clear and dose latitude.

Paper Details

Date Published: 16 May 1994
PDF: 8 pages
Proc. SPIE 2195, Advances in Resist Technology and Processing XI, (16 May 1994); doi: 10.1117/12.175398
Show Author Affiliations
Louis C. Poli, Army Research Lab. (United States)
Christine A. Kondek, Army Research Lab. (United States)

Published in SPIE Proceedings Vol. 2195:
Advances in Resist Technology and Processing XI
Omkaram Nalamasu, Editor(s)

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