In-situ monitoring of thickness of quartz membrane during batch chemical etching using a novel micromachined acoustic wave sensor

This work presents a novel method based on the surface acoustic wave (SAW) device for monitoring in-situ the thickness of quartz membrane during batch chemical etching. Similar to oscillators and resonators, some SAW devices require the thickness of quartz membranes to be known precisely. Precisely controlling the thickness of a quartz membrane during batch chemical etching is important, because it strongly influences post-processing and frequency control. Furthermore, the proposed micromachined acoustic wave sensor, allows the thickness of a quartz membrane from a few μm to hundreds of μm to be monitored in-situ. In particular, the proposed method is highly appropriate for monitoring in-situ a few μm thick quartz membranes, because the thickness of a quartz membrane is proportional to the phase velocity. In summary, the proposed method for measuring the thickness of quartz membrane in real time, has high accuracy, is simple to set up and can be mass produced. Also described herein are the principles of the method used, the detailed process flows, the measurement set-up and the simulation and experimental results. The theoretical and measured values differ by an error of less than 2 μm, so the results agreed with each other closely.