Thickness measurements and uncertainty evaluation of a multilayer thin-film sample using auxiliary single-layer samples

Abstract

Multilayer thin-film structures are widely used for many different types of devices in the semiconductor, display, and battery manufacturing industries. In such devices, the thickness of each layer should be strictly controlled to meet desired performance requirements. Various measurement techniques have been utilized to take thickness measurements, but verification of these measurements continues to rely on simple comparisons. In this study, for an uncertainty evaluation of a multilayer thin-film structure, a four-layer multilayer sample (SiO2-SiN-SiON-SiO2) with each layer having a nominal thickness of 100 nm was fabricated together with auxiliary single-layer thin-film samples fabricated at the time of each deposition step for each layer. The multilayer sample and auxiliary samples (ASs) were measured using a calibrated spectral reflectometer, after which their interference spectra were analyzed to determine their thicknesses through a model-based analysis. Based on the measurement results, the uncertainty of the multilayer sample was evaluated by considering two components: the uncertainty of the AS, which included the thickness analysis resolution, measurement repeatability, and thickness uniformity; and the thickness offset between the four-layer multilayer sample and the ASs. Finally, the measurement uncertainties of the thin-film thicknesses in the multilayer sample were evaluated and found to be 10.8 nm at the first layer, 9.8 nm at the second layer, 7.8 nm at the third layer, and 3.3 nm at the fourth layer.