A Comparison of Thickness Values for Very Thin SiO2 Films by Using Ellipsometric, Capacitance-Voltage, and HRTEM Measurements

Abstract

A comparative study of very thin film thickness values obtained from the three dominant measurement techniques used in the integrated circuit industry, ellipsometry, capacitance-voltage (C-V) measurements, and transmission electron microscopy (TEM) has been completed. This work is directed at evaluating the metrology capabilities that might support the development of thickness reference materials for very thin dielectric films. We used a variety of models to analyze ellipsometry measurements and used three different quantum-mechanical-based algorithms to account for substrate quantized states and depletion effects in the polysilicon electrode to analyze the C-V results. TEM measurements were conducted by both phase contrast high resolution (HRTEM) and atomic number contrast high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). We found a range of thickness values with each of the methods, with an overlap of values among the three techniques. HRTEM and STEM values showed less consistency between wafers than did ellipsometry or C-V, and seemed to be influenced more by local variations such as interface nonuniformities. We present sources of variation and estimates of the primary components of uncertainty for the measurements employed and discuss the implications of these results for obtaining consistent and unified film thickness metrology and for possible reference standards.