Black silicon morphologies using conventional RIE processing

We report on the use of conventional non-Bosch, non-cryogenic Reactive Ion Etching (RIE) processing to produce a range of low optical reflection morphologies on silicon wafer. Tapered structures and nano dendritic-pillars are patterned into silicon over a pressure range of 550 - 700 mTorr at various run times. Low pressure RIE conditions yield tapered profiles while at higher pressures nano-pillars are produced. The optimized condition of 650 mTorr for 20-30 minutes yields uniform distribution of nano dendritic pillars resulting in a low average reflectance of 4.2% – without an additional antireflective coating. A simple kinetic Monte-Carlo model shows that nano-dendritic structures can be formed due to low etching rate of side walls and evolve into tapered structures over a longer run time. Refractive index profiles built from our simulated patterns and surface morphology of the samples yield calculated reflectance curves that correlate well with experimental results.