The most direct coating control method is the quartz crystal micro balance method (QCM), which can be directly driven by the evaporation source, through the PID control loop drive baffle, keep the evaporation rate. As long as the instrument is connected with the system control software, it can control the whole process of the coating. But the accuracy of (QCM) is limited, in part because it monitors the quality of the coating rather than the thickness of the film.
In addition, although QCM is very stable at low temperature, but the temperature is high, it will become very sensitive to temperature. In the long process of heating, it is difficult to prevent the sensor from falling into the sensitive area, thus causing significant errors.
Optical monitoring is the preferred method of monitoring for high precision coating, because it can accurately control the thickness of the film (if used properly). The improvement of accuracy is due to many factors, but the most fundamental reason is the monitoring of optical thickness.
Theoptimal SWA-I-05 single wavelength optical monitoring system, using indirect control, according to Dr. Wang developed advanced optical monitoring software, effectively improve the optical response of film thickness sensitivity of theory and methods to reduce the ultimate error provides feedback and transmission mode selection, and a wide range of wavelength monitoring. Especially suitable for all kinds of thick film coating monitoring including non regular film monitoring.