Fast, Smooth Etching of Silicon with SF₆: Sulfur Plays a Role

Researchers etched silicon (Si) with plasmas containing different percentages of sulfur hexafluoride (SF₆). High-resolution topography images with the Cypher ES AFM showed that increasing SF₆ yielded not only faster etching rates but also smoother surfaces, ascribed to surface-adsorbed sulfur atoms.

Fluorine-containing plasma treatments are widely used to rapidly etch Si, for instance to create high-aspect-ratio features in micro-electromechanical systems (MEMS). Among these, SF₆ plasmas have been found to etch up to 100 times faster than others, but the reasons why have not been clarified.

To explore this topic, researchers at the University of Houston (U.S.) and Samsung Electronics (South Korea) etched Si with varying ratios of nitrogen trisulfide (NF₃) to SF₆ in NF₃/SF₆/Ar plasmas. AFM measurements of surface roughness and structure showed that in addition to enhancing the etching rate, increasing SF₆ led to smoother surfaces. Additional experiments suggested that both effects could be explained by adsorbed sulfur atoms acting as catalysts.

The processing insight gained from this study could improve manufacturing of advanced devices across a range of semiconductor and microelectronic applications.

Instrument used

Cypher ES

Techniques used

Topography images of nanoscale height were acquired in tapping mode with the Cypher ES AFM. The Cypher’s low noise floor and high spatial resolution ensured measurements with high accuracy. The images were also analyzed with the Cypher’s built-in software to determine RMS surface roughness as a function of SF₆ percent.

Citation: P. Arora, T. Nguyen, A. Chawla et al., Role of sulfur in catalyzing fluorine atom fast etching of silicon with smooth surface morphology. J. Vac. Sci. Technol. A 37, 061303 (2019). https://doi.org/10.1116/1.5125266

Note: The data shown here are reused under fair use from the original article, which can be accessed through the article link above.