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.
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. A37, 061303 (2019). https://doi.org/10.1116/1.5125266
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