Characterization of wafer-level XeF2 Gas-phase Isotropic Etching For MEMS Processing

This paper reports the characteristics of wafer-level XeF₂ gas-phase etching. Compared with chip-level XeF₂ etching, the silicon etch rate for wafer-level XeF₂ process is much smaller, which is mainly caused by the large exposed silicon area in wafer-level process. Additionally, the silicon etch rate drops off as etching time increased. The aperture size effect is apparent in wafer-level XeF₂ processing. However, for etching window with large size, the aperture size effect will be minimized. The vertical aperture size effect is direct proportion to the number of etch cycle, while the lateral aperture size effect is first increase then decrease with the number of etch cycle increasing. Slight anisotropy of wafer-level XeF₂ etching is also observed. Based on the characteristics of XeF₂ etching, layout design rule for MEMS device with XeF₂ releasing is developed and demonstrated.