Characterisation of the long-term reproducibility of 2D coordinate photomask calibration at the PTB

Over the last decade the PTB has offered traceable pattern placement calibrations on two-dimensional measurement objects, like e.g. photomasks; by means of a modified optical mask measurement system. The measurement uncertainties achieved on high quality objects with measurement lengths of up to 150 mm are 30 nm for one-dimensional length measurements and 35 nm for the determination of coordinates of structures placed on plane substrates. We report on the long-term reproducibility of the calibration results, especially with respect to the disseminated length scale, as determined by means of recalibrations of customer masks.