Updated NIST photomask linewidth standard

NIST is preparing to issue the next generation in its line of binary photomask linewidth standards. Called SRM 2059, it was developed for calibrating microscopes used to measure linewidths on photomasks; and consists of antireflecting chrome line and space patterns on a 6 inch quartz substrate( 6 in. x 6 in.,x 0.25 in. for 15.2 cm x 15.2 cm x 0.635 cm). Certified line- and space-widths range from nominal 0.250 gm to 32 mum, and pitches from 0.5 mum to 250 mum, and are traceable to the definition of the meter. NIST's reference value, the definition of the meter, is well defined and unconditionally stable. Any replacement or duplicate NIST linewidth standard will be traceable to this same reference, and thus traceable to any other NIST length standard. Establishing such traceability requires evaluation of the effects of all error sources affecting the calibrations. While the meter (and the mum) are well-defined, the geometrical width of a chrome line with nonrectangular cross section is not, and so the "true value" linewidth must be carefully defined to best meet users' needs. The NIST linewidth measurement system and the optical imaging model used have both been updated for this SRM. Remeasurements of previous NIST SRMs 473 and 475 reveal discrepancies which are difficult to reconcile with previous international comparisons between NIST, NPL, and PTB.