Improved full-field rotating analyzer ellipsometry method for ultrathin film characterization

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 Psi and Delta, are less than 0.045 deg, with a lateral resolution of 4.65 mu m. 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. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)