Improvement of side-wall roughness in deep glass etched MEMS vibratory sensors

In this paper we report an optimized post-fabrication annealing process for improvement of sidewall roughness in deep glass etched resonant MEMS devices. The method utilizes thermal-reflow behavior of glass and does not require chemical or mechanical treatment. Experiments were conducted to explore the trade-off space between roughness improvement and structural deformation by varying temperature from 300 °C to 900 °c and duration from 2 to 240 minutes. The optimal results were obtained at 700 °C for 30 minutes, resulting in an 10x improvement in roughness from 900 nm Ra to 85 nm Ra and low feature deformation of <;10%. The method was successfully utilized in deep glass etching of micro-glassblown wineglass resonators, which resulted in very low side wall roughness and sub-hz frequency symmetry.