CMOS-Compatible Wafer-Level Double-layer Silicon Nanograss through Reactive Ion Etching for Applications in Optics

The modulation of the surface of silicon stimulates its applications in optics (antireflection surface, solar cells, and photoelectric devices). In this work, an appropriate ratio of the O₂ to SF₆ plasma through reactive ion etching generated a double-layer Silicon nanograss (upper layer─flocculent SiO_xF_y passivation; lower layer─pointy silicon spike) on the surface of the silicon wafer. The height and density of Silicon nanograss can be controlled through process parameters (pressure, O₂/SF₆ ratio, and RF power), mask spacing, and a variety of assistant substrates. The underlying formation mechanisms of Silicon nanograss disclosed that the sputtering of Al substrate acts as a micromask, i.e., primarily responsible for the formation of Silicon nanograss. Considering an in-depth study, a simple, low-cost, and CMOS-compatible method for wafer-level preparation of Silicon nanograss is provided. Specifically, the Silicon nanograss exhibited excellent antireflection and enhanced absorption properties. This work contributes to micro-nano surface science accompanied by optical applications.