Two-dimensional photomask standards calibration

In a joint project with LEICA LMW, the PTB has developed a standard comparator based on the LMS 2000 mask measuring machine. The properties of the machine and the objects (mask standards) were investigated. Means for error corrections were derived and the traceability to the unit of length is achieved. 7 inch photomask standards consisting of two dimensional arrays of crossed lines are calibrated with respect to x/y locations, length, straigthness orthogonality. The positions of each cross is certified with an uncertainty better than 50 nm x 50 nm. Thus, for the first time a calibrated two dimensional mask standard with appropriate uncertainty has become available.