Fabrication of silicon nanostructures with large taper angle by reactive ion etching

Abstract

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

Surface Nanostructures Formed by Phase Separation of Metal Salt–Polymer Nanocomposite Film for Anti-reflection and Super-hydrophobic Applications

“…Hence, we modified the etching process to fabricate such cone-shaped pillars. Previously, we have reported inductively coupled plasma reactive ion etching (ICP-RIE) of silicon to give a broadly tunable tapered profile or even a negatively tapered profile (inverse cone shape) [ 28 , 29 ]. Using the reported etching recipe, resulted structures are shown in Fig.…”

Batch fabrication of AFM probes with direct positioning capability

“…Therefore, here, we employed a nonswitching pseudo-Bosch process that can give a smooth sidewall with a tunable sidewall taper angle by adjusting the ratio of SF 6 and C 4 F 8 gas. 8 With the optimal ratio of SF 6 /C 4 F 8 ¼22:38, a smooth vertical etching profile can be obtained, with a silicon etching rate of 390 nm/min and a high etching selectivity between Si and Al of 100:1. 9 Next, the probes were dipped into 1:20 diluted hydrofluoric (HF) acid for 2 min to remove the remaining Al layer.…”

Hut-Like Pillar Si Solar Cells

“…A lift-off process was used to create a regular array of 10-nm-thick chrome discs for use as an etch mask in plasma etch process. An SF6/C4F8 plasma was used to create the tapered Si rods using the following parameters: 20 W RIE, 1200 W ICP, 5/55 sccm gas ratio, pressure 10 mTorr [8]. These parameters gave an etch rate of ~50 nm/min with a DC bias of ~100 V. We will report further experimental results of the hut-like pattern and compare them with simulations.…”