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Barium Fluoride and Strontium Fluoride Negative Electron Beam Resists

Research Area: Nanofabrication Year: 1987
Type of Publication: Article Keywords: electron beams, masking, lithography, gallium arsenides, barium fluorides, strontium fluorides, etching, electron collisions, resolution
Authors: Axel Scherer; H. G. Craighead
Journal: Journal of Vacuum Science and Technology B Volume: 5
Number: 1 Pages: 374-378
Month: January
The suitability of strontium and barium fluoride as electron beam resist materials has been studied. Their sensitivity to high energy electron beams was measured, and the exposure mechanisms were described using scanning transmission electron microscopy. The effect of crystallite size and film composition on the exposure and development conditions of these inorganic resist systems were investigated. Finally, these resists were directly used as etch masks on gallium arsenide, and their performance was evaluated. Both barium and strontium fluoride were found to be sensitive negative resists, requiring exposure doses of 25–100 µC/cm2. The resolution of pure strontium and barium fluoride is limited by the grain size of the original fluoride deposits. The resolution and development conditions were improved by deposition of a mixture of barium and strontium fluoride (of approximately 50 at. % BaF2 in SrF2), which yielded line resolutions of better than 100 nm. All of these fluorides are extremely resistant to reactive ion etching with halogen containing gases and can be used as etch masks to pattern GaAs.
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