Improvement of thickness uniformity of quartz crystal wafer by numerically controlled plasma CVM

Abstract

To improve the thickness uniformity of thin quartz crystal wafer, new machining process which utilizing an atmospheric pressure plasma was developed. In an atmospheric pressure plasma process, since the kinetic energy of ions which impinge to the wafer surface is small and the density of reactive species is large, high efficiency machining without damage is realized. In this process, thickness distribution of the quartz crystal wafer is corrected by numerically controlled machining which consists of two steps. First, long spatial wavelength component of thickness error is corrected by using a cylindrical rotary electrode. And next, short wavelength component is corrected by using small size pipe electrode. By using our two step correcting process, thickness distribution of an AT cut wafer was improved from 108 nm (p-v : peak to valley) to 14 nm (p-v). And spurious mode in the resonance curve was reduced by improving the parallelism of the quartz crystal wafer.