As semiconductor manufacturing technology progresses and the dimensions of integrated circuit elements shrink, overlay budget is accordingly being reduced. Overlay budget closely approaches the scale of measurement inaccuracies due to both optical imperfections of the measurement system and the interaction of light with geometrical asymmetries of the measured targets. Measurement inaccuracies can no longer be ignored due to their significant effect on the resulting device yield. In this paper we investigate a new approach for imaging based overlay (IBO) measurements by optimizing accuracy rather than contrast precision, including its effect over the total target performance, using wavelength tunable overlay imaging metrology. We present new accuracy metrics based on theoretical development and present their quality in identifying the measurement accuracy when compared to CD-SEM overlay measurements. The paper presents the theoretical considerations and simulation work, as well as measurement data, for which tunability combined with the new accuracy metrics is shown to improve accuracy performance.
In this publication the authors have investigated both theoretically and experimentally the link between line edge roughness, target noise and overlay mark fidelity. Based on previous worki , a model is presented to explain how any given edge of a printed feature could have a mean position that varies stochastically (i.e., randomly, following a normal distribution) due to lithography stochastic variation. The amount of variation is a function of the magnitude of the LER (more accurately, all the statistical properties of the LER) and the length of the feature edge. These quantities have been analytically linked to provide an estimate for the minimum line length for both optical and e-beam based overlay metrology. The model results have been compared with experimental results from wafers manufactured at IMEC on both EUV and ArF lithographic processes developed for the 10 nm node, with extrapolation to the 5 nm node.