Bilateral comparison of 25 nm pitch nanometric lateral scales for metrological scanning probe microscopes

One-dimensional (1D) and two-dimensional (2D) gratings are some of the most important transfer standards for the calibration of nanometrological instruments. National Metrology Institutes (NMIs) demonstrate their calibration capability through international comparisons among themselves and provide pitch calibration services for their customers. In the past, international comparisons were performed three times for gratings with large pitches such as 4000 nm, 1000 nm, 700 nm and 300 nm. Additionally, a bilateral comparison was conducted for 100 nm and 50 nm between the Japanese National Metrology Institute (NMIJ) and the German National Metrology Institute (PTB). The industry, however, requires calibration services for increasingly smaller pitches. In a previous study, NMIJ developed a nanometric lateral scale, a special 1D grating with 25 nm pitch consisting of Si/SiO2 multilayer thin-film structures, and calibrated the pitch of this scale by using the NMIJ's atomic force microscope equipped with differential laser interferometers (DLI-AFM). In this paper, we will report results of an informal bilateral comparison for the nanometric lateral scale between NMIJ and PTB.