Nanoscale directional etching features and mechanism of HF/HNO₃ etchant

Large-scale and periodic silicon nanostructure arrays are an essential component for various functional devices. However, the conventional selective etching mechanism of specific crystal faces for monocrystalline silicon generally achieves slope or vertical morphology, which greatly limits the preparation of other morphology of silicon nanostructures. In this work, the conventional isotropic etchant HF/HNO₃ has successfully achieved nanoscale directional etching and cambered morphology on monocrystalline silicon surface for the first time by changing the synchronous process of oxidation and dissolution into an asynchronous process. Based on the self-assembled monolayer colloidal crystal templates, large-area and high-quality nanopore arrays are prepared on the monocrystalline silicon surface. Particularly, the directional etching ability of HF/HNO₃ etchant is further confirmed by combining with electron beam lithography and scanning probe lithography technologies. Hence, this nanoscale directional etching mechanism and etchants provide a promising strategy to achieve cambered morphology nanopores on the monocrystalline silicon surface. (paper)