UV light from ambient environment increases the \mathrm{Si_3N_4} etch rate in \mathrm{XeF_2} etching

Abstract

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Releasing mechanical structures is a fundamental step in MEMS processing. Given the wide usage of silicon nitride ( \mathrm{Si_3N_4} ) on silicon (Si) carrier due to high stress and high mechanical Q factors, high etching selectivity between \mathrm{Si_3N_4} and Si is very crucial for the release process. Here we demonstrate that UV light from ambient light sources in a cleanroom environment (EPFL - CMi) can increase the etch rate of \mathrm{Si_3N_4} using \mathrm{XeF_2} , therefore reduce the selectivity to the substrate (Si). By blocking the top window of the \mathrm{XeF_2} etching chamber and blocking the light, we see enhancement by a factor of 3 in the selectivity between \mathrm{Si_3N_4} and Si.

References

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[1] Sugano, Koji, and Osamu Tabata. "Etching rate control of mask material for XeF2 etching using UV exposure." Micromachining and Microfabrication Process Technology VII. Vol. 4557. International Society for Optics and Photonics, 2001.