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Quartz Crystal Microbalance Measurement Instruments
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Quartz Crystal Microbalance (QCM) Measurement Instruments have been used in thin film vacuum deposition since the 1960`s and have proven to be very useful for almost all thin film deposition and etching processes including physical and chemical vapor deposition from thermal sources, e-beam guns, sputter guns, magnetrons, ion guns and laser sources. QCM systems themselves range from simple manually controlled single film monitors to fully automated, multi-layer controllers that control the entire thin film vacuum deposition process. INFICON provides a complete line of QCM thin film vacuum deposition equipment to meet all of these needs.
What equipment is required?
A complete QCM system requires a measurement instrument, a sensor head to hold the crystal, a feedthrough to pass the water and electrical connection through the chamber wall, an oscillator and a few cables to connect everything together. For simple applications, deposition monitors are used to provide continuous rate and thickness data and automatic source shutter control. More advanced applications require thin film vacuum deposition controllers which provide enough capability to completely automate the entire deposition process.
How QCMs are used?
As mentioned above, QCMs can be used to monitor almost all vacuum deposition and etching processes including physical and chemical vapor deposition from many types of sources. However, some processes may not require QCM monitoring because they are very repeatable or only require post run adjustments to maintain the desired level of accuracy. Other processes may only require use of a QCM during the setup and calibration stages of the development. In the majority of applications, the QCM is used during the deposition for every layer of every process.
There are some important considerations that must be made when determining the applicability of the QCM. First, remember that the QCM only measures the rate and thickness changes on the sensor crystal not the substrates. Therefore, a successful application of the QCM must include a consistent relationship between the deposition rate on the crystal versus the rate on the substrates. Second, the life of the sensor crystal is material limited meaning it will fail once a sufficient amount of material has been deposited. Although periodic sampling techniques can extend the range of the crystal, some processes involve so much material that the QCM simply is not a practical solution. For that reason, QCMs are not normally used in roll coaters.
A typical deposition system requires one or more sensor head and feedthrough combinations connected to the measurement instrument. Sensor head placement is critical because as mentioned above, the accuracy of the QCM is primarily defined by the consistency between the deposition rate on the sensor versus the rate on the substrates. Typically, the sensor head is installed near the center of the chamber in the same plane as the substrates and is orientated so the sensor crystal has a direct line of sight view of the source.
The sensor head and feedthroughs are connected to either a deposition monitor or controller depending on the required level of automation. Typically, the instrument provides the user interface which includes a display of deposition rate and thickness. Most deposition controllers also display source power, process time and other process data as well as real time graphs to aid in the fine tuning of the process. Some instruments also include computer interfaces and PC based software, which provides the ability for complete computer control including data logging, process archiving and many other features.
Once installed, the QCM will require some programming and calibration runs to determine the source conditioning parameters and material tooling factors. With the programming completed, the QCM should provide years of service with very little sensor head maintenance except for the routine changing of the sensor crystal.
Learn more about our QCM products:
Thin Film Deposition Controllers, Monitors and QCM Instruments
Sensors and Feedthroughs
Pocket Indexer
Quartz Crystals
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Sensor and Feedthrough Packages
Precisely the right sensor or feedthrough for your process.
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