Size-controllable fabrication of nano-to-microstructures on silicon surface using high-density ion etching with pulsed bias

A `black silicon´ (BS) surface with low reflectance was fabricated by a standard pulsed deep reactive etching technology at room temperature. Aiming for a better understanding, a systematic experiment was conducted by varying the etching window size and bias power duty cycle. The samples were measured and analysed by a scanning electron microscope, the Bruker Optical Profiler and a UV-3400 spectrometer. It was observed that a broad scale range of the surface structures formed on the surface. With the duty cycle at 0.5, only about 100 nanometre scale replicable silicon cones formed on the surface, but as the duty cycle decreased to 0.25, the height of the silicon forest sharply increased to about 10 μm, leading to a low reflectance of 0.9% in the visible range for the surface. To clarify the reason for this trend, the bias effective voltage (BEV) was measured and it was confirmed that the BEV would decrease from 100 to 47 V with the duty cycle adjusted from 1 to 0.25. This suggested that this decrease in BEV leads to a reduction of ion energy and ion flux, and then modifies the fabricated structures. Besides, it was found that the broad etching window area only had a maximum promotion of 20% to the scale of the BS, indicating this method was almost free of loading effect.