Controllable formation and optical characterization of silicon nanocone-forest using SF6/C4F8 in cyclic etching-passivation process

This paper reports a nanocone-forest silicon surface fabricated by an improved DRIE process using SF₆/C₄F₈ in cyclic etching-passivation process, which is maskless, controllable, effective and large-size. As well known, optical property of textured silicon surface is determined mainly by its surface structure, and surface structure is determined by process conditions. In this work, process conditions during the experiment, like etching process parameters, pretreatment, uniformity control and patterned silicon etching, are tested and discussed. Based on these controllable process conditions, nanocone-forest with an average height of 0.4~5μm, aspect ratio of 1~8 and density of 3~30 per 4μm² formed. By analyzing the influences of nanostructure parameters on optical property, it´s concluded that high aspect ratio, high density and small height of nanostructure could result in ultra-low reflectance. The optical reflectance of two samples has been reduced to below 0.22% and 0.16% of the solar spectrum, respectively.