Deep Wet Etching of a Z-Cut α-Quartz Wafer by Fluorine-Based Solutions: Experiment, Mechanism, and Application

Quartz is an indispensable material in microelectromechanical system (MEMS) technology to manufacture miniaturized oscillators and sensors. The fabrication process of quartz, however, encumbers its development for extensive applications, as it is difficult to ideally control processed dimensions. Although dry etching or other special machining techniques have been profoundly researched, wet etching is still the most practical and cost-effective method to obtain desired structures. In this study, z-cut $\alpha $ -quartz wafers were etched by ammonium bifluoride solutions of different concentrations at various temperatures, and the etched results including depth, roughness, and morphology were measured, calculated and analyzed. Subsequently, the tendency of the etched results with respect to temperature and concentration reflected the correlation of conditional parameters on the etched results, and suggested that the distinction of roughness at a specific etched depth was insignificant despite the variation in etchant concentration. Additionally, the etched results were analyzed further to reveal the etching mechanism of different fluorine-based solutions. At last, the pendulum of quartz resonant accelerometer was fabricated by different etchants, and their mechanical and thermal performances were compared, indicating that smoother etched surface is beneficial to realize appropriate sensitivity and optimize thermal stability. These investigations provide quantitative data and qualitative analyses to improve the deep wet etching process in terms of design, manufacture, and performance for quartz MEMS devices. [2025-0007]