The Research And Achiecement Of Real-time Monitoring System Of Optical Thin Film Thickness

Accuracy of the monitoring of opcitcal thin film determines the accuracy of film thickness, with the development of industry, the thickness accuracy of film gets higher, especially in communications, the bandwidth of narrow band filters are usually less than 1nm, and which need dozens of layers with high and low refractive index material deposited. The optical monitoring of optical thin film thickness has automatic compensation function, so the opcial monitor is used for depositing narrow band filters, and which is the background of this paper. To the optical monitoring, There are a lot key technical difficulties te be fixed, which are the light source instability,the stray light in the coating machine, the process of distorted data of signal which is acquired, and ultimately, high-precision judgment of extreme points.The thesis carried out as follows: First, the software simulation using MATLAB during the deposition process of film coating materials, and then using LabVIEW simulated the transmission or reflection change over time, using phase Lock-In Amplifier for noise suppression and signal demodulation, using NI PCI-6281 data acquisition card acquire coating machine's main signal and reference signal, through Savitzky-Golay smoothing filter processing the signal acquired, removal of high frequency noise, and then get the relatively stable signal. This paper also discussed optical transmittance or reflectance curve hanges over time, through comparing found that fitting modle of Fourier series function has the minimum error. Eventually normalized film system monitoring methods used to determine extreme points, respectively, by the mere use of the main signal, every second request as a means of monitoring the voltage at this time, and then obtained by fitting the extreme point, this monitoring the final accuracy of 2nm, another kind of monitoring is to use the main signal and reference signal for phase-locked amplification, followed by the same curve fitting, the final monitoring accuracy is 1nm, achieved the desired target.