@misc{oai:niigata-u.repo.nii.ac.jp:00033901,
 author = {Luo, Songjie},
 month = {2020-07-02, 2020-07-02},
 note = {The white-light scanning interferometry is a kind of the three-dimensional measurement technology for surface profile and thickness of thin film. Because of the features of large measurement range, fast measurement speed, non-invasive and high precision, the white-light scanning interferometry becomes a preferable technology to measure the surface profile and the thickness of thin film. However the dispersion phase caused by the changing refractive index of optical components with different wavelengths in white-light scanning interferometers makes the measured optical path difference (OPD) of zero imprecise. The random noise generated by the vibration also makes the OPD instable. In order to eliminate these disturbances, a serial of research are proposed to improve the measurement accuracy in this dissertation. Main research and innovations of this dissertation are as follows: (1) Utilization of complex-valued interference signal (CVIS) in white-light scanning interferometer (WLSI). Fourier transform and inverse Fourier transform are performed on the white-light scanning interference signal to obtain the complex-valued interference signal. The zero phase position Z_p nearest the maximum amplitude position Z_a obtained from the complex-valued interference signal is proposed as the new measurement value. (2) Dispersion phase elimination by using spectral analyzer. The dispersion phase in WLSI is obtained from the real-valued interference signal detected by spectral resolved interferometer (SRI) through the Fourier transform. The dispersion phase in the SRI is subtracted from the spectral phase in Fourier transform of the CVIS of the WLSI. Through inverse Fourier transform of this spectral distribution, a dispersion-free CVIS is obtained, and the position Z_p provides a surface profile with an error less than 4 nm. The repeatability of three measurements in an interval of about 10 min is 1.2 nm. (3) Dispersion phase elimination by using a least square line in spectral phase distribution. Since the capture and process of the interference signal from SRI before the measurement of surface profile makes the experiment complicated, a new signal processing is proposed to eliminate the dispersion phase simply. After Fourier transform of interference signal in the WLSI, the spectral phase of interference signal is obtained in wavenumber domain. The linear and bias components in the spectral phase distribution are used to calculate the complex-valued interference signal (CVIS) by inverse Fourier transform. This signal processing without using a measured dispersion phase provide a surface profile with an error less than 4 nm. The repeatability is 1.3 nm (4) Interference signal correction by detection of scanning position. In order to obtain the surface profile with higher accuracy than the result obtained from research (3), it is necessary to eliminate the random vibration of optical components and non-linear movement of PZT in the experiment. The actual OPD is detected with an additional interferometer in the WLSI by using an optical band-pass filter. The interference signal of the WLSI is corrected with the real OPD values or the real scanning position values. By this correction method, a surface profile with a step shape of 3-μm height is measured accurately with an error less than 2 nm. The repeatability is about 0.5 nm. (5) Compensation of dispersion effect in shape measurement of thin glass plate. In shape measurement of a thin glass plate the rear surface profile cannot be measured by the method of the research (3) because the dispersion effect exists in the glass plate. The position Z_p of amplitude maximum in the CVIS is not equal to the position of the rear surface. From simulation results it is made clear that the positions Z_a and Z_p are proportional to the rear surface position or the thickness of the glass plate. The proportional coefficients for Z_a and Z_p are determined to C_a=1.53612 and C_p=1.51506, respectively, by the simulations. By using the C_a and C_p, the errors of measured front and rear surface profile are less than 4 nm, and the measured thickness has an error less than 4 nm and the repeatability is 2.4 nm., 新大院博(工)甲第498号},
 title = {Research on advanced signal processing in a white-light scanning interferometer for exact measurements of surface profile and film thickness},
 year = {}
}