The Dissolution Behavior of Silicon in Aqueous HF-(HCl)-HClO3-Mixtures: Reactivity Studies, Analytics of Etching Solutions and Surface Morphologies

Solutions containing hydrofluoric acid (HF), chloric acid (HClO3), and hydrochloric acid (HCl) are investigated as novel acidic, nitrogen oxide (NOx)-free mixtures for wet-chemical etching of silicon wafer surfaces. HF-HClO3-H2O solutions exhibit etching rates of only up to 0.12 µm min‑1 at room temperature, as the oxidizing agent chlorate (ClO3-) is not very reactive. In contrast, aqueous HF-HClO3-HCl mixtures show etching rates of up to 10.78 µm min‑1 at room temperature, as chlorine (Cl2) and chlorine dioxide (ClO2) are formed, which also serve as oxidizing agents. Depending on the HCl content isotropic or anisotropic etching behavior occurs, resulting in polished or textured surfaces with upright, inverted, and rounded pyramids. The solutions and gas phases were analyzed using Raman spectroscopy. In addition, the resulting silicon surfaces were analyzed using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM).