Surface tension and its role for vertical wet etching of silicon

In this paper, we present for the first time a systematic investigation of the role of the surface tension in anisotropic wet etching of silicon, focusing on the sidewall angle. We show that in the KOH and NaOH solutions with high surface tension a reliable fabrication of vertical sidewalls is possible. Etching experiments on (1 0 0)-Si and surface tension measurements via bubble pressure tensiometry were conducted using inorganic etchants in a wide range of concentrations. Finally, the surface tension of the etching solutions was identified as an important quantity that determined the etching behavior, while concentration dependences were eliminated by controlling the surface tension using temperature.