Harnessing sulfur hexafluoride for clearer and more efficient plasma etching

Nanofabrication engineers often rely on fluorocarbon-based plasmas to etch silicon dioxide (SiO₂), but polymerization from these chemistries can cause non-uniformity and process drift. Bernet et al. demonstrated that sulfur hexafluoride (SF₆), which does not polymerize, can still achieve anisotropic etching of SiO₂ and improve the fabrication of oxide structures.

The authors achieved comparable etch rates to traditional methods while reducing the gas needed by more than 100 times. Etch dynamics followed Paschen’s law, a fundamental principle in plasma physics that predicts the voltage needed for plasma to ignite at different pressures. The etch rate reached a maximum at a pressure of roughly 10 millitorr, a commonly used pressure for etching. Finally, the study found that chromium masks, which enable fine-grained patterns to be etched by protecting underlying materials, are highly selective towards silicon dioxide, reducing processing time and tool contamination.

“An exhaustive parametric study is performed where all possible parameters influencing the etch were considered,” author Marc Bernet said. “We believe this to be valuable experimental data, especially for other engineers working within the field of plasma simulation lacking sufficient experimental plasma etch hardware.”

All experiments were conducted in a commercially available plasma etch tool restricted to SF₆, fluorine, oxygen, helium, and argon gases. This setup ensured clean conditions and reliable data. The researchers followed a detailed experimental plan to explore parameter spaces and the development of new methods to test the hypotheses.

In follow-up research, the group is focusing on improving sustainability by investigating molecular fluorine plasmas, which can deliver comparable performance while eliminating global warming concerns.

Source: “Highly selective anisotropic dry etching of smooth SiO₂ nanostructures using SF₆ plasma and Cr hard mask: Toward sustainable plasma etching,” by Marc Bernet, Kristian Buchwald, Dines Nøddegaard, Jörg Hübner, Rafael Taboryski, Henri Jansen, Journal of Vacuum Science & Technology B (2026). The article can be accessed at https://doi.org/10.1116/6.0005027 .