Formation mechanism of multi-functional black silicon based on optimized deep reactive ion etching technique with SF6/C4F8

This paper reports a controllable multi-functional black silicon surface with nanocone-forest structures fabricated by an optimized deep reactive ion etching (DRIE) technique using SF6/C4F8 in cyclic etching-passivation process, which is maskless, effective and controllable. The process conditions are investigated by systematically comparative experiments and core parameters have been figured out, including etching process parameters, pre-treatment, patterned silicon etching and inclined surface etching. Based on the experimental data, the formation mechanism of nanocone shape is developed, which provides a novel view for in-depth understanding of abnormal phenomena observed in the experiments under different process situations. After the optimization of the process parameters, the black silicon surfaces exhibit superhydrophobicity with tunable reflectance. Additionally, the quantitative relationship between nanocones aspect ratio and surface reflectance and static contact angle is obtained, which demonstrates that black silicon surfaces with unique functional properties (i.e., cross-combination of reflectance and wettability) can be achieved by controlling the morphology of nanostructures.