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Fabrication of sub-micron trenches with surfactant-added KOH

The effects of surfactant added to potassium hydroxide (KOH) on the etch parameters for the fabrication of trenches in nano scale are presented in this study. Different amounts of dihexyl sodium sulfosuccinate (SDSS) surfactant were added to a KOH solution used to fabricate nanotrenches and their effect on the trench depth and width were systematically investigated. It was observed that addition of SDSS to KOH for all amounts tested resulted in increased trench depth and reduced trench width, which both led to better aspect ratio and etch anisotropy. Among different surfactant amounts used, a solution of 0.04 wt % SDSS in 50 wt % KOH resulted in enhanced etch depth uniformity, highest trench depth and narrow trench width, with the best aspect ratio and etch anisotropy. The trench depth increased from 26.5µm to 31.1µm whereas the trench width decreased from 564 nm to 361 nm with the 0.04 wt % SDSS in 50 wt % KOH. As a result, the etch rate anisotropy enhanced more than a factor of 2 from 133 to 317. This is attributed to the surfactant enhancing hydrogen bubble release during KOH etching. Moreover, the surfactant adsorbs more strongly on the atomically smooth Si(111) surface of the trench sidewalls, which considerably hinders the lateral etch rate. The electrostatic repulsion between the anionic surfactant molecules and hydroxyl ions may also be a factor in the reduction of the etch rates.