The simulated grating for absolute measuring the transfer function of large-aperture Fizeau interferometer is proposed, combining with the surface and homogeneity absolute measurement data, the simulated grating absolute surface data without aberration can be obtained more accurately to achieve the full aperture transfer function absolute measurement at all spatial frequency. A 300mm aperture Fizeau interferometer experimental results show that the absolute surface errors of the three flats are less than λ/20(PV) and λ/100(RMS), and the homogeneity measurement is better than 1*10-6. The optimized transfer function is better than 0.86 at 1 mm-1 spatial frequency, which is a 10% improvement.
Optical testing is constantly evolving, necessitating higher lateral resolution in interferometry. Achieving high resolution leads to longer processing times, significantly impacting testing efficiency. The unwrapping phase algorithm is crucial in interferometry, but its complex calculations can impede efficiency improvements. There are two types of algorithms for the unwrapping phase: path-dependent and path-independent. Path-dependent algorithms tend to be more efficient, and thus, we have chosen to utilize the accelerated path-dependent algorithm. Among these algorithms, Goldstein's algorithm is widely applied. This study uses CPU-GPU heterogeneous computing to parallelize and accelerate the Goldstein phase unwrapping algorithm while maintaining acceptable numerical error limits. Our proposal focuses on optimizing the serial Goldstein algorithm for GPU architectures by parallelizing and enhancing three key steps: residue identification, branch cutting, and integration. Specifically, our optimization approach leverages GPU shared memory and SIMD functionality. To assess the efficiency of our proposed method, we conducted tests on the unwrapped phase image with varying pixel sizes. The results demonstrate that as the pixel size increases, the performance gain from GPU computation becomes more pronounced compared to CPU computation. Using a 4096×4096 phase diagram on the RTX3070 laptop hardware, we achieved a 60x speed increase in the overall process compared to the CPU version. Therefore, employing this algorithm with the GPU can significantly expedite the phase unwrapping process and enhance the efficiency of interferometry.
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.
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.
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.
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