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.
We describe an improved approach for accurately characterizing the thickness distribution of ultrathin films by using full-field rotating analyzer ellipsometry. The significant improvements originate from the combination of angle optimization and error compensation. Angle optimization is achieved by fixing the polarizer and the quarter wave plate (QWP) at the averaged values of a series of optimal angles, which correspond to a certain thickness range of the sample. At the same time, error compensation further improves the accuracy by determining and removing the nonuniform impact of the QWP. To verify the applicability of the proposed method, experiments based on varied ultrathin films are implemented and compared with the results of two conventional methods. The results from the proposed method are in accord with those obtained using commercial instrument and the design value in thermal evaporation system. Further investigation shows that the uncertainties of the ellipsometric angles, both Ψ and Δ, are less than 0.045 deg, with a lateral resolution of 4.65 μm. Because of its improved accuracy, this method offers a feasible route for characterizing film thickness, especially in the case of monitoring the growth of thin layers from a bare substrate or following changes in the sample parameters during a kinetic process.
A 2-dimensional thickness measurement ellipsometer based on the liquid crystal variable retarder (LCVR) is proposed and setup in order to provide precise, real-time measurement in a manufacturing environment. Images are collected sequentially by CCD camera with respect to pre-determined polarization state of incident light derived by the LCVR attached with compensator. A phase-shifting algorithm and a Fourier series approach algorithm are used to obtain full-field distributions of the ellipsometric parameters, and then a polarization model (ambient-film-substract) is used to calculate the thickness of a thin film in two dimensions precisely and quickly. Theoretically, the speed and precision of this method benefit from applying voltage on the LCVR to produce polarization modulation that is able to avoid mechanical vibrations that could affect the accuracy of the measurements. The experimental results verify the ability and performance of the 2-dimensional thickness measurement ellipsometer.