Results of a round robin measurement on a new CD mask standard

We report on the results of a recent round robin comparison on new linewidth or CD photomask standards in which several partners from different companies and institutes in Germany were involved. The round robin activity is at the end of a joint project targeting at the development of a new CD mask standard and it was intended to show the performance of the CD mask standard and to test its application in cross-calibration processes. Different type of CD metrology instrumentation was used, namely optical transmission microscopy including water immersion CD microscopes with NA of 1.2 and scanning electron microscopy, supported by additional scanning probe microscopy (SPM/AFM) characterizations. A set of differently processed CD mask standards with smallest line and space structures down to 0.1 μm and based on different mask blanks was produced with identical layout. At the PTB this set of CD standards was calibrated by UV transmission microscopy and by CD-SEM as well. For the round robin an unknown CD mask of the same design as the standards was used and the participants were asked to provide measurement data with their CD metrology tools, referred to their respective PTB calibration standards. It will be shown, that the agreement of measurement data between different CD metrology tools can be significantly improved if proper definitions of the measurand and a metrologically sound approach to signal modelling and interpretation of CD measurement values is applied. The outcome of this comparison provides a valuable source of information for cross calibration issues which are discussed in mask industry today and, moreover, it proves the performance of the newly developed CD mask standard, which now is available to other interested parties, too.