When it comes down to instrument specifications for 3D metrology, very few really contribute to the ultimate goal of measuring a component with the highest quality and accuracy possible.  Two key specifications are vertical and lateral resolution as they say how shallow and narrow a feature one can measure.  Vertical resolution can typically be measured through examining the noise floor from multiple measurements.  For lateral resolution, the Instrument Transfer Function (ITF) is a metric used to represent the fidelity of measurement quality over different period structures. This ability to measure the surface height variation of a test sample as a function of the feature size is a critical metric of an interferometer, and has become a popular way to compare interferometers on the market.  But how are each measured in practice and how do they affect the results?

This presentation will answer the above questions and provide examples of how results differ as resolution changes.  It will also discuss why it is important to qualify 3D optical systems with known methods and standards, and some practical considerations when doing such measurements.  It will also include actual examples of where lack of resolution leads to very different views of the acceptability of a test piece and the implications in accepting a poorly-measured component.