Wet Etched High Aspect Ratio Microstructures on Quartz for MEMS Applications

Abstract

Z cut α-quartz wafers were etched in saturated ammonium bifluoride solution at 87 degrees C. The side wall profiles were observed using the scanning electron microscopy (SEM) and plotted dependent on the polar direction. This research focused on investigating high aspect ratio trench and through-hole, which were dependent on the polar direction to the crystal axis. Aspect ratio in dependence on polar direction was also plotted and microchannels with aspect ratio > 3 could be achieved at the polar angle between 30° to 60°. The possibility of application for microcapillary was discussed, and the trench at 45° was considered best. Double-sided etching technique was used for manufacturing through-hole structures. Through-hole at 0° was demonstrated effective for fabrication of capacitive MEMS tilt sensor. Through-holes at 15° and 105° were proposed for fabrication of 90°-arranged two axis capactive tilt sensor, taking advantage of the twofold symmetry property around X axis and threefold symmetry property around Z axis.

Evolutionary continuous cellular automaton for the simulation of wet etching of quartz

“…The selected etchant is saturated NH 4 HF 2 at 85 • C. The etch rate distribution for this etchant has been obtained by modifying the etch rate data of the same etchant at 80 • C [11], based on the overall reactivity and anisotropy of the main planes at 85 • C, as extracted from Ref. [15]. After the evolutionary calibration For a more quantitative comparison, we perform an extensive computational study that resembles the actual experiment presented in section 3.1 of Ref.…”

“…After the evolutionary calibration For a more quantitative comparison, we perform an extensive computational study that resembles the actual experiment presented in section 3.1 of Ref. [15]. The experiment consists in the etching of a set of 24 grooves, each rotated 5 degrees with respect to the previous one ( figure 8(a)), covering a total range of 120 • (3-fold symmetry).…”

“…The angles and rates have been used traditionally to characterize the quartz etch rate distribution, providing complete information about the etch profiles for differently oriented grooves. Figure 9 shows a comparison of the sidewall angles and rates for the calibrated CCA model and the experiment [15]. Although the overall match is excellent, some small differences can be pointed out, including: (i) V 1 and V 2 are slightly faster in the simulations (roughly 10%), (ii) for grooves oriented in the range 30 • ≤ β ≤ 90 • the facets 2 and 3 are distinguished in the experiment as slightly different sidewalls (in orientation and etch rate) while they are merged into the same facet in the simulations, and (iii) for grooves oriented in the range 100 • ≤ β ≤ 115 • the angle α 2 and etch rate V 2 show a discontinuity at 105 • in the experimental results while a smooth behavior is found in the simulations.…”

“…The structures require long etch times and, thus, the prolonged competition between various slow planes that must be calibrated accurately. Figure 10 compares the simulated groove profiles and the experiment [15]. The mask opening is 5 µm and each groove is rotated 5 degrees with respect to the previous one.…”

“…Although the complex anisotropy of the process has been analyzed in multiple studies [11,12,13,14,15], only limited efforts have been made in order to obtain reliable models that properly describe the quartz etch anisotropy [11,13]. Based on geometric methods, the already existing models show a limited accuracy, resulting specially problematic in certain situations, such as the intersection of planes or wafer perforation.…”