Development of Tomographic Imaging and Fitting Methods for Critical Dimension Measurement of TFT-LCD

Abstract

In this paper, two methods are introduced to enhance the repeatability of critical dimension measurement on certain micro pattern by using White-light Phase Shifting Interferometry (WLPSI). Since WLPSI collects the coherence signal by vertically scanning the sample, the repeatability of WLPSI is often affected by external noise like mechanical vibrations. The external interference to the machine causes numerical error on the measured data. Profile Fitting method is introduced to enhance the repeatability. The fitting parameters are calculated by using iterative non-linear fitting process, Levenberg-Marquarts nonlinear fitting algorithm. Once the fitting parameters are determined, the sampled cross sectioned profile of the mirco-pattern can be interpolated smoothly by fitting process which eventually eliminate possible error factors at the source data. During the Profile Fitting method, the critical dimension data from tomographic image is utilized. Based on the reason, the repeatability of tomographic CD measurement should be stable to achieve for better repeatability. Gaussian Fitting method is suggested for the tomographic image acquisition process to eliminate possible noise properties on the modulus function. In order to evaluate the performance of suggested methods, multiple measurements of pattern samples are conducted.