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The use of quartz crystals (often called quartz crystal microbalances, or QCMs) to monitor the deposition of thin films by vacuum processes has been an industry norm since the late 1960's. By measuring the resonance frequency of an oscillating crystal, one can determine the thickness of a metal or dielectric coating to within 1 Angstrom. This has proven to be an invaluable tool for process control and manufacture of optical and solid state electronic devices.
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Due to its frequency-temperature behavior, however, quartz is limited to operating temperatures of 100 º C or less, and in most cases, must be water cooled to insure accurate and reproducible readings. Unfortunately, many advanced thin film coating processes operate in significantly hotter environments, including chemical vapor deposition (CVD), Atomic Layer Deposition (ALD) and Electron Beam Epitaxy (MBE). In such cases, the performance of the existing quartz crystals has been simply inadequate.
With the invention of single crystal gallium orthophosphate, or GaPO4 , this temperature limit had been significantly raised, to a practical operating ceiling of 800ºC. This opens up new possibilities for thin film research and process control. An immediate application is the real-time monitoring of low temperature CVD of oxide materials using a precursor material such as tetraethylorthosilicate (TEOS), for example. A GaPO4 microbalance crystal can be heated, in a suitable sensor holder, to the decomposition temperature of TEOS. As the TEOS breaks apart, leaving a thin film of silicon oxide, the crystal frequency changes and is monitored by a commercial film thickness monitor.
About the co-operation
Piezocryst Advanced Sensorics GmbH and Virginia Beach Sensors LLC. entered into a broad collaboration arrangement on thin film monitoring equipment on February 2007. This co-operation combines the strengths of both companies to one center of excellence developing superior solutions to the surface coating community. As first products new thin film sensors for high temperature coating processes are offered, that enable monitoring of layer thicknesses at temperature levels that could hardly be addressed in the past. This new technology will help cutting production costs and increase process efficiency in almost any high temperature coating process including molecular beam epitaxy, chemical vapor deposition and atomic layer deposition.
Piezocryst contributes its unique gallium phosphate crystal technology and its know-how in high temperature sensors, whereas Virginia Beach Sensors adds its specific application know-how and the marketing expertise to this partnership. The companies partner in a way that Piezocryst develops and manufactures high temperature resonators and sensors while Virginia Beach Sensors takes the exclusive responsibility for the worldwide marketing of the sensing devices.
For more information please visit: www.virginiabeachsensors.com
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