The positions of the traditional three-position spherical absolute measurement are the cat's eye position, the confocal position, and the confocal position rotated 180°. Rotational operation can introduce misalignment errors that affect the measurement results. In this paper, it is shown that only two measurements of cat's eye position and confocal position are necessary to obtain the absolute surface of the measured sphere through Zernike polynomial fitting. When solving the three-position spherical absolute measurement with Zernike polynomials, the number of unknowns is greater than the number of equations, resulting in the inability to solve. By analyzing the equation, the relationship between the Zernike coefficients before and after rotation can be found, resulting in a solvable system of equations.
In the phase-shifting interferometry, the surface phase diagram is corrected by spectral analysis of the ‘intensity-phase pattern’ (the relationship between the interference intensity and the measured phase) of each phase-shifting image to achieve the purpose of reducing the vibration effect. This spectrum analysis algorithm is different from the previous methods. It does not determine the phase diagram, but corrects the phase diagram obtained by PSI measurement. It has few restrictions on the surface shape, and unlike the spatial Fourier method, it does not require high-density spatial carrier fringes, although at least a fringe of phase departure is recommended. The error between the influence of the simulated vibration signal on the phase and the influence of the actual measurement signal on the phase is less than 5 %.
A dual-beam Fizeau interferometry with both small and large aperture two measurement modes is proposed. The two modes of the interferometer were measured and analyzed using three-flat four-step absolute measurement and three-flat simulated sinusoidal phase grating. An integrated 4″-18″ aperture dual-beam Fizeau interferometer was used to perform experiments on large and small aperture by the above two measurement methods. The experimental results show that the absolute surface errors of the three flats are less than λ/20(PV) and λ/100(RMS), and the transfer function is better than 0.78 at the 1 mm-1 spatial frequency, which satisfies the specification.
The vibration of wafers can significantly impact the accuracy and efficiency of wafer inspection, especially when the wafer is placed vertically. And the larger the wafer size, the thinner the thickness, the more obvious its vibration. To improve the efficiency and accuracy of wafer inspection, and also to make wafer inspection more adaptable to the complex inspection environment and reduce the cost of inspection, this study through a large number of experiments to find out the main factors that lead to vibration of the vertically placed wafers, such as temperature changes, mechanical vibration, environmental disturbance, airflow disturbance, and fluid-solid coupling. The main method is to analyze the vibration law of the wafer through the vibration of the interference fringes produced when the wafer is affected by different disturbing factors during the interferometry process. After effectively controlling the above interference factors in the wafer inspection process, the practical data of wafer surface shape can be measured continuously and stably.
KEYWORDS: Fizeau interferometers, Wavefronts, Control systems design, Control systems, Switching, Optical transmission, Equipment, Wavefront errors, Visualization, Signal detection
To address the problem that the traditional multi-wavelength wavefront detection requires manual adjustment of mechanical devices and low automation, this paper proposes a multi-wavelength laser interferometer control system with the Fizeau-type interferometer principle as the background, using Visual Studio to establish the upper computer control interface on the computer and sending signals to the microcontroller through the serial port to control the interferometer. Among them, the main controls are the switching of fluorescence alignment plate in 1064nm laser, the translation drive of collimating lens within 2mm of Z-axis, the automatic adjustment of variable diaphragm and the variable adjustment of CCD. The system realizes the automatic switching of five wavelengths of the multi-wavelength laser interferometer by controlling the precision motor, which reduces the error caused by manual adjustment and improves the measurement accuracy and efficiency of the interferometer.
In this paper, we mainly use the basic principle of Fizeau interferometer, because Fizeau type interferometer has the advantage of common optical path, which can reduce the influence of some system errors to a certain extent, and the requirements for environmental changes are relatively low, and then use zemax optical simulation software to simulate the cat's eye position, confocal position and confocal rotation 180 degree position in the three position absolute detection method, and establish the absolute measurement model . Through the combination of simulation and simulation, it is concluded that the measurement error mainly includes tilt error, translation error and defocus error. Among them, the tilt error and translation error have negligible impact on the system measurement results, and the defocus error has a greater impact on the measurement results. Finally, the defocus error is removed by a new higher-order defocus removal method.
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