Effect of oxygen plasma cleaning on nonswitching pseudo-Bosch etching of high aspect ratio silicon pillars

Abstract

In dry plasma silicon etching, it is desired to have a high etching rate, a high etching selectivity to mask material, a vertical or controllable sidewall profile, and a smooth sidewall. Since the standard Bosch process (switching between SF6 and C4F8 gases) leads to a wavy/rough sidewall profile, the nonswitching pseudo-Bosch process is developed to give a smooth sidewall needed for nanostructure fabrication. In the process, SF6 and C4F8 gases are introduced to the chamber simultaneously. Here, the authors show that by introducing a periodic oxygen (O2) plasma cleaning step, that is, switching between SF6/C4F8 etching and O2 cleaning, the silicon etching rate can be significantly improved (by up to ∼55%, from 139 to 216 nm/min) without any adverse effect. This is mainly because O2 plasma can remove the fluorocarbon polymer passivation layer at the surface. The etching and cleaning step durations were varied from 5 s to 40 min and from 0 to 60 s, respectively. The fastest etching rates were obtained when the cleaning step takes roughly 10% of the total etching time.

Fabrication of Large-Area Silicon Spherical Microlens Arrays by Thermal Reflow and ICP Etching

“…During ICP etching, selected gases entering the etchi chamber generate high density plasma via glow discharge under the effect of the elect field, and the plasma density is affected by the power of the coil (ICP power). Then, t ionized plasma is accelerated by the bias voltage generated by the CCP generator to bo bard the wafer downward, thereby removing the surface material physically and chem cally [43][44][45][46][47]. We chose SF6, C4F8, and O2 to be injected simultaneously as process gas where SF6 and O2 were mainly used for etching silicon and the photoresist, respective The addition of C4F8 increased the anisotropy of the etching process, which incidenta slowed down the etching rate.…”

Inductively Coupled Plasma Dry Etching of Silicon Deep Trenches with Extremely Vertical Smooth Sidewalls Used in Micro-Optical Gyroscopes

“…As the cycles continue, the trench depth increases, while the sidewalls remain vertical, thanks to the presence of the passivation film. In the pseudo-Bosch process, SF 6 and C 4 F 8 are injected simultaneously; therefore, etching and passivation are performed together [40,41]. The cryogenic process operates below −100 • C and adopts O 2 as the passivation gas, working concurrently with SF 6 .…”