Improvement of the Thickness Distribution of AT Cut Quartz Crystal Wafer by Open-air Type Plasma Chemical Vaporization Machining

We developed an open-air type atmospheric pressure plasma machining system for fabricating the ultra-precision optical components or for finishing the functional materials. In the case of the atmospheric pressure plasma, high density plasma region is localized in the vicinity of the electrode because of its small mean free path. Therefore, free figuring without mask pattern is realized by scanning the localized reactive area. And the plasma process is insensitive to the external vibration compared with the conventional mechanical machining process, because the plasma process is a non-contact process. Furthermore, expensive utilities, such as a process chamber or a vacuum pump, are not necessary, so that a cost-effective ultra-precision machining system can be constructed. We applied this system for finishing the thin AT cut quartz crystal wafer which was manufactured by conventional mechanical cutting, lapping and polishing. As a result of the correction machining of the thickness distribution, we achieved thickness uniformity of 50 nm level by one application of the proposed process.