The existing estimation methods for recovering height information from surface gradient are mainly divided into Modal and Zonal techniques. Since specular surfaces used in the industry always have complex and large areas, considerations must be given to both the improvement of measurement accuracy and the acceleration of on-line processing speed, which beyond the capacity of existing estimations. Incorporating the Modal and Zonal approaches into a unifying scheme, we introduce an improved 3D shape reconstruction version of specular surfaces based on Phase Measuring Deflectometry in this paper. The Modal estimation is firstly implemented to derive the coarse height information of the measured surface as initial iteration values. Then the real shape can be recovered utilizing a modified Zonal wave-front reconstruction algorithm. By combining the advantages of Modal and Zonal estimations, the proposed method simultaneously achieves consistently high accuracy and dramatically rapid convergence. Moreover, the iterative process based on an advanced successive overrelaxation technique shows a consistent rejection of measurement errors, guaranteeing the stability and robustness in practical applications. Both simulation and experimentally measurement demonstrate the validity and efficiency of the proposed improved method. According to the experimental result, the computation time decreases approximately 74.92% in contrast to the Zonal estimation and the surface error is about 6.68 μm with reconstruction points of 391×529 pixels of an experimentally measured sphere mirror. In general, this method can be conducted with fast convergence speed and high accuracy, providing an efficient, stable and real-time approach for the shape reconstruction of specular surfaces in practical situations.
This work proposes a point-specific self-calibration method to characterize film thickness distribution by exploiting the multiple detection capability of a home-built full-field ellipsometer. The self-calibration method offers a feasible route for retrieving calibration information from the actual real-time sample measurement in conjunction with the ellipsometric parameters, thus leading to error-free data after the elimination of systematic errors and addressing the problem of high time-consumption. With the help of the multiple detection capability of a full-field ellipsometer, we can further implement self-calibration for every point-specific pixel, termed as point-specific self-calibration to achieve a high-accuracy film thickness profile. The synthetic thickness distribution composed of structural-anisotropy pixels with tilted surface is utilized to demonstrate the potential of the proposed approach by retrieving the ellipsometric angles and the calibration parameters of every single pixel. A three orders-of-magnitude improvement in the accuracy of thickness determination was achieved in the simulation. To demonstrate the feasibility of the proposed approach, a SiO2 film deposited on the Si substrate is measured in this work. This approach could be easily extended to implement thickness distribution measurements accurately and rapidly in other rotating-element ellipsometer cases.
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