Research Of Multi-Wavelength Coating Monitoring System Based On Vacuum

Optical thin-film has been widely used in research and in our life. Manufacturing high-performance thin-film requires not only advanced coating technology, but also excellent film monitoring technique. This paper introduced several commonly used methods in the current for preparing films and methods for film deposition monitoring. Among the optical thickness monitoring methods, the turning point monitoring approach of photo-electricity is a method that was studied early and appled maturely. With the purpose of practical application, this paper developed a multi-wavelength vacuum coating monitoring system based on optical extreme value method. The monitoring system includes two parts:hardware and software.Hardware consists of multi-wavelength selection circuit and the main circuit board. The multi-wavelength selection circuit section is designed to place the electromagnetic-mechanical optical switches that receiving high and low control signals to switch laser source. The main circuit board includes peripheral circuits centered the AN2131SC which possesses an8051microcontroller core and an USB core. According to the function of the hardware, hardware circuit is devided into three modules:Multi-wavelength selection module, signal acquisition and processing module, control and transmission module.Software system contains microcontroller firmware and PC applications software. The firmware is responsible for management of single-chip microcontroller, transmitting control signals to each peripheral circuit to switch laser source and complete A/D conversion. Besides, hardmware uploads digital monitoring data and reference data alternately by adding different logos. PC applications software achieved human-computer interaction. As a source of various control commands, PC sends control commands to start or stop monitoring system, helps single-chip system to work. Most importantly, the PC application software receives digital data uploaded from microcontroller. After analysis and processing, PC maps out the film thickness changes in real time curve on the human-computer interactive interface.The differential curve of the real-time monitoring signal curve can help to find when the extreme value will turn up. The differential curve has the same horizontal axis with the monitoring signal and the vertical axis represents the difference between two adjacent monitoring signal points. The amount of the difference component means the thin-fime growth speed, the positive and negative sign mean the transmittance of the source increases amd decreases. Besides, adjusting the maximum on the image can improve the observability of the curve.