Study On Technology Of Thin Film Thickness Measurement Based On Space Carrier Frequency Interferometry

Modern interferometry and measurement for thin-film thickness has the advantages of noncontact, high accuracy and rich-field, etc. Many precision measuring rely on optical interferometry, for some test mission, interferometry even is the sole correct solution.In this article, interferometry of space carrier frequency is discussed based on the FFT method. This paper illustrates how to unwrap phase with single interferogram. Twyman-Green interferometer and CCD images receiving equipment are harnessed to acquire interferogram with thickness of the film. The relationship between interferogram and measured material object parameter can be determined by mathematical model, thus the thickness of measured material object is measured automatically with digital image processing technology. A set of algorism for interferogram processing is design, this includes:removing the noise, edge detection, region spreading, frequency domain transformation and phase unwrapping. Frequency domain transformation:2D-FFT is used to transfer interferogram from spatial domain to frequency domain. Appropriate filter is used to withdraw the first order spectrum. Then, we use 2D-FFT transfer the interferogram from frequency domain to spatial domain again. The distribution of wave surface wrapped phase with the measured thin film information can be derived by 2D-IFFT in frequency domain. Then, the wrapped phases must be unwrapped in the thin film and base area. They include a novel algorism namely "algorism of diamond phase unwrapping".The algorisms of the thesis are not only used to test the concrete thin film interferograms, but also used to test the gauge block interferograms for verifying the algorisms. Then, the results of data processing and the results of ZYGO interferometer are contrasted, it indicate that the height, PV and RMS values of the measured thin film, which is processed by the algorithm processing software are 113.8nm,0.4189λand 0.091λrespectively. The height, PV and RMS values are 113.0nm 0.430 and 0.093λrespectively by using the ZYGO interferometer to measure the same film. In this way, the algorisms of the thesis not only save time, but also reduce the complexity of unwrapping wave surface, thus the thickness of measured material object is measured automatically in the real-time case. It has important and practical significance on optimizing the preparation process of thin film.