Micro-and nanostructures with a tapered sidewall profile are important for antireflection and light trapping applications in solar cell, light emitting diode, and photodetector/imager. Here, the authors will show two etching processes that offer a large taper angle. The first process involved a maskless etching of pre-etched silicon structures having a vertical profile, using a recipe that would give a vertical profile when masked. The authors obtained a moderate taper angle of 14 using CF 4 /O 2 etching gas. The second process involved a one-step etching step with Cr as mask using a recipe that was drastically modified from a nonswitching pseudo-Bosch process that gives a vertical profile. The gas flow ratio of C 4 F 8 /SF 6 was greatly increased from 38/22 to 59/1 to result in a taper angle of 22. Further reduction of the RF bias power led to an unprecedented large taper angle of 39 (at the cost of greatly reduced etching rate), which is even higher than the angle obtained by anisotropic wet etching of silicon. V
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