Real-time spectrum measurement in thin-film thickness wideband monitoring system

In a thin-film thickness wideband monitoring system, a grating spectrometer is utilized to disperse spectrum and the linear CCD is used to quickly finish spectrum scanning to control the thin-film thickness, which satisfies the requirements of the real-time monitoring. However, the accuracy of spectrum scanning directly affects the availability of the thin-film thickness real-time monitoring. In order to obtain precise spectrum information, the corresponding relationship between CCD pixel and spectral wavelength was determined. Based on the discrete relationship between characteristic spectral lines and pixels, the spectrum calibration function was established using the least-square fitting method, and the root-mean-square error of calibrated wavelength was 0.037 nm by experiment. Then aiming at the spectral monitoring signal from CCD output in real-time, the wavelet threshold filtering optimization algorithm was applied to suppress the random noise and the spectrum signal details were well reserved, the maximums of peak error and peak location error were 1.0% and 0.3% respectively, which satisfied the spectral resolution requirements.