Fig. 1. Schematic diagram of the overall structure of the optical control system

Fig. 2. Optical control hardware device

Fig. 3. Schematic diagram of signal conversion

Fig. 4. Functional structure of optical film thickness monitoring system

Fig. 5. Logic flow chart of film thickness monitoring system in optical control software

Fig. 6. Comparison chart of brightness value curves

Fig. 7. Non-linear fit test software program

Fig. 8. Comparison of fitting curves for film thickness monitoring. (a) Polynomial film thickness monitoring fitting curve; (b) fitting curve of film thickness monitoring with absorption

Fig. 9. Filtering algorithm test software program

Fig. 10. Comparison of original and filtered signals. (a) Raw signal; (b) signal after median filtering; (c) S-G filtered signal

Fig. 11. Filtering algorithm order test software program

Fig. 12. Comparison plot of S-G filtered signals with different orders. (a) Third-order signal; (b) fourth-order signal; (c) fifth-order signal

Fig. 13. Optical monitoring design curve

Fig. 14. Difference between actual film thickness and design film thickness

Fig. 15. Comparison of actual test light control spectral curve