Multistage chemical etching for high-precision frequency adjustment in ultrahigh-frequency fundamental quartz resonators.

Chemical etching to precisely adjust and to make uniform the thicknesses of vibrating areas of multiple resonators in a single wafer was applied to inverted-mesa quartz resonators exciting an ultrahigh-frequency fundamental thickness vibration. The process consisted of five stages, combining high-rate etching for high productivity and low-rate etching for high-precision adjustment. By using this process, the resonance frequencies of 41 resonators in the single wafer were adjusted to 620 +/- 1.5 MHz, which corresponds to vibrating area thicknesses of 2.2 microm +/- 6 nm. In the temperature-frequency characteristics of these resonators in the single wafer, the difference between the maximum first-order temperature coefficient and the minimum first-order temperature coefficient was equivalent to a cut angle change of two arcminutes. In addition, vibrating areas with an arithmetic mean surface roughness of 0.17 nm on the concave side were produced by this multistage etching.