Uncertainties in Nanometer-Scale Dimensional Metrology
John S. Villarrubia
These are slides used for an oral presentation made at the NIST "Workshop on Quantification of Uncertainties in Material Science." In nanometer-scale dimensional metrology, correction of probing errors, which are caused by the characteristic left/right symmetry of edges, have led to the adoption of model-based metrology in such measurement techniques as optical scatterometry, critical dimension small angle x-ray scattering (CD-SAXS), and model-based scanning electron microscopy. In these techniques the measurand is related to a measured signal via a model function or algorithm. Because the measured signal often has low information relative to needs, "hybrid" or combined metrology, wherein multiple techniques are combined, may be attempted. The presentation describes two unsolved uncertainty quantification issues that arise in this context: estimation of the uncertainty contributed by modeling error and, for combined metrology, from methods divergence (systematic differences between metrology methods).