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.
Wafer, the primary material used to make semiconductor chips, are found in almost every type of electronic device used in everyday life. As the quality of wafer used in large-scale integrated circuits has improved considerably, the diameter of wafer has continued to increase, and the thickness of silicon wafer has become increasingly thin. Wafer manufacturers and device manufacturers are increasingly focusing on wafer thickness variation. In the past few years, the usual capacitive tools for wafer inspection have been replaced by interferometric tools for higher sensitivity and resolution. We, therefore, describe a method that uses two Fizeau-type phase-shift interferometers to simultaneously measure the front and back surfaces of a vertically placed wafer and calculate the thickness variation of the wafer based on the resulting morphologies. The reliability of the method was verified by comparing the wafer thickness variation obtained from experimental measurements with that obtained from optical glass bonding. Over three days, five consecutive measurements were performed daily on 50mm wafer using this method, and the experimental results showed that the average values of RMS (Root Mean Square) of the thickness variation calculated for each day were 41.843nm, 40.751nm, and 40.490nm, and the average values of PV (Peak to Veally) were and 206.761nm, 205.252nm, and 209.800nm, and the measurements proved to be highly reproducible. The method has good stability and reliability to meet the measurement of wafer thickness variation.
An illumination system for coherent noise suppression is envisioned. The principle of coherent noise suppression is introduced, and this illumination system is designed this way. The illumination system is simulated, and the hybrid sequence model of Zemax analyzes the irradiance. To verify the noise suppression effect of this illumination system, it is used as the illumination part of the Fizeau interferometer. The interference process is simulated under the nonsequential model of Zemax to obtain an off-axis light source with a ring radius of 0.32 mm and a numerical aperture of 0.14. The Fizeau interferometer with a conventional light source is also simulated. A comparison experiment is set up to generate the same noise point in the two interferometers using different illumination modes to trace and produce the same four interference fringes with the same interferometric cavity length of 20 mm and the same tilt angle of the measured surface of 0.057°. Compared with the interferograms in the conventional illumination mode, the interference fringes formed by the illumination of this study are almost undamaged, and the near-complete interference information can be retained. The interferometer system with this light source was built and the test results were verified, and it was found that it could achieve the measurement accuracy of 1/20 wavelength and the measurement stability of 1.219 nm, and it also had a good contrast of interference fringe.
Ring elements are of great significance in the field of precision machining, and their performance is crucial for the functionality of the whole system. However, the present frequent inspection of such components lacks effective means and is prone to causing damage to the component. In view of this, this article on the basis of comprehensive research, combined with the principle of optical interference detection, puts forward a measuring method for such components, the method by introducing a pyramid to realize high precision optical path, and according to the inner surface in the shape of different components, it can be divided into cylinder and circular arc surfaces, respectively, measuring scheme is designed. Then, according to the designed inspection scheme, the system is built separately for inspection. After the system is stable, the shape information of the tested part is obtained. After the system is stabilized, the shape information of the inspected part is obtained. The shape information of the inner surface of the ring element can be obtained after only one inspection.
KEYWORDS: Interferometry, Control systems design, Calibration, Interferometers, Control systems, Switching, Switches, Interfaces, Microsoft Foundation Class Library, Channel projecting optics
The traditional interferometry method of large aperture optical elements relies on changing the beam expansion lens and optical path structure artificially according to different test samples, which inevitably introduces some systematic errors. Therefore, this paper proposes a corresponding dual-wire control scheme according to the functional requirements and simulation experiments of dual-optical path interferometer. This scheme is based on serial communication protocol and Zigbee communication protocol. Through the coordination of Zigbee wireless control, serial software control and mechanical structure, the optical path can be folded and calibrated for many times, so that the changing position of the optical element after each switch of measurement aperture is fixed. The real-time status is displayed in the interactive interface developed based on MFC (Microsoft Foundation Classes). Finally, the whole system is tested and verified. The results show that the system can basically complete the real-time debugging of the optical path, which provides a practical design idea for the automatic control of the hybrid interferometer in the future.
Digital interferometer is widely used for evaluating optical surfaces due to its outstanding sub-nanometer accuracy and precision. In this paper, we will summarize its advantages and then describe its applications in industry, especially in both absolute flat and cylindrical surface and measurements. Transmission flat has normally 1/20 wavelength PV. However, when a flat surface under test is better or much better than the transmission flat, we need the absolute flat measurement. We developed a method to be easily able to achieve the accuracy of 1/100 wavelength PV. Two different measurement methods are proposed for the surface shape measurement of the inner surface and the outer surface of the cylinder, and the circular data is converted into rectangular data. For off-axis aspheric surfaces, we also propose a new measurement method. We have dedicated our efforts to do so. The theoretical analysis and experimental validation are presented in the paper.
Interferometry repeatability is an important indicator for measuring instrumentation and test results. The precondition of improving the detection accuracy is to ensure high-precision repeatability, so high-precision repeatability is one of the most important indicators in precision detection. In the Fizeau interferometer, common light paths are used for the distances from the laser light source to the reference surface, from the reference surface to the detector CCD, and the reference beam and the test beam. However, the strict sense of the co-beam does not exist, and it is not absolute ideal that reference plane has high-precision surface. The test beam reflects from the measured surface will have a certain angular deviation from the reference beam. If so, it may make the reference beam and the test beam reach the CCD detector along different optical paths and generate return error accordingly. And finally it makes effects in sampling and wave surface reproduction. Therefore, using the Zygo GPI system, the 4D system and the H and L system to make research on the same optical platform for relative interferometry repeatability comparison, ensuring that the cavity length is the same, and the standard reference mirror and the tested mirror is the same. Measurements were repeated 50 times for zero-stripes, five-stripes, and ten-stripes. The PV values and RMS values of the 50 measurements make mean processing to reflect the measurement repeatability. Further repeatability error analysis is performed on the phase shift algorithm and PZT phase shifter.
Digital interferometer is widely used for evaluating optical surfaces due to its outstanding sub-nanometer accuracy and precision. In this paper, we will summarize its advantages and then describe its applications in industry, especially in both absolute flat and cylindrical surface and measurements. Inner surfaces measurement of cylindrical ring can be achieved without map stitching, by a Fizeau interferometer with a 90° conical mirror. The alignment of this arrangement, however, is very crucial to the accomplishment. Any small misplacement of 90° cone or hollow cylinder from their ideal settings may result in large measurement errors. These errors are not intuitive and hard to be removed if their origins are not well understood. In other words, it is very important to know how these measurement errors are generated from the optical misalignment in order to eliminate them. Transmission flat has normally 1/20 wavelength PV. However, when a flat surface under test is better or much better than the transmission flat, we need the absolute flat measurement. We developed a new method to be easily able to achieve the accuracy of 1/100 wavelength PV. We have dedicated our efforts to do so. The theoretical analysis, computer simulations, and experimental validation are presented in the paper.
Higher accuracy of optical surface measurement is needed with the rapid development of optical industry and technology, especially in the field of optical manufacture and optical metrology. Fizeau interferometery is widely recognized as one of the most important measurement techniques currently in use. Results of the Fizeau interferometeric testing contain the reference surface errors and test surface errors. The test accuracy is restricted by the error of reference surface. As a result, so-called absolute flatness testing technology must be used to eliminate the system error such as reference surface error and higher accuracy of the surface profile testing. In this paper, the theory formula of even and odd functions is deduced, and the method are programmed for simulation. Based on HOOL phase-shifting interferometer, experiments are done to achieve high accuracy flatness measurement. The experiment shows that with high-accuracy interferometer, absolute flatness testing technology can effectively calibrate reference surface and improve the accuracy of flatness surface testing. An important result of this experiment is that the accuracy of the test surface can be reached λ/50.
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