Most optical results, such as composition/concentration, etc., are based on indirect measurements extracted using a model-based approach. Although the metrological performance of such measurements is satisfactory for most cases, they become inadequate as the semiconductor industry moves toward ultrathin layers and complex multi-stacks. In those circumstances, x-ray metrology solutions are becoming popular not only as lab solutions, but also as inline metrology solutions. High-resolution x-ray diffraction (HRXRD), x-ray fluorescence (XRF), x-ray reflectance (XRR), and x-ray photoelectron spectroscopy (XPS) are some of the techniques that are being developed for use (at various level of maturity) in inline metrology. Table 7.1 is a high-level summary of these four techniques, along with application use-cases and their strengths/challenges.
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