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

Abstract

Micro-optical gyroscopes (MOGs) place a range of components of the fiber-optic gyroscope (FOG) onto a silicon substrate, enabling miniaturization, low cost, and batch processing. MOGs require high-precision waveguide trenches fabricated on silicon instead of the ultra-long interference ring of conventional F OGs. In our study, the Bosch process, pseudo-Bosch process, and cryogenic etching process were investigated to fabricate silicon deep trenches with vertical and smooth sidewalls. Different process parameters and mask layer materials were explored for their effect on etching. The effect of charges in the Al mask layer was found to cause undercut below the mask, which can be suppressed by selecting proper mask materials such as SiO2. Finally, ultra-long spiral trenches with a depth of 18.1 μm, a verticality of 89.23°, and an average roughness of trench sidewalls less than 3 nm were obtained using a cryogenic process at −100 °C.

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.…”