Accurate and traceable calibration of two-dimensional gratings

TLDR

Accurate, traceable calibration of 1D and 2D gratings is essential for nano‑ and microtechnology, yet optical diffractometers can measure mean pitch but not uniformity. The study aims to quantitatively measure both mean pitch and uniformity of gratings using a large‑range scanning probe microscope. The authors used a large‑range scanning probe microscope, applying gravity‑centre and Fourier‑transform data‑evaluation methods, correcting cosine error, and calibrated multiple 1D gratings. The calibrated mean pitch values agree excellently with optical diffractometry, while SPM data revealed grating irregularities and demonstrated the gratings’ utility for calibrating a typical SPM.

Abstract

Accurate and traceable calibration of lateral standards (1D and 2D gratings) is a basic metrological task for nano- and microtechnology. Both the mean pitch and the uniformity of the gratings should be measured quantitatively. Although optical diffractometers are effective for measuring the mean pitch, they are not able to measure the uniformity of gratings. In this study, the calibration of gratings is performed using a metrological large range scanning probe microscope with optimized measurement strategies. Two different kinds of data evaluation methods, a gravity centre method and a Fourier transform method, have been developed and investigated. Cosine error, a significant error source of the measurement, is analysed and corrected. Calibrations on several 1D gratings have been carried out. The calibrated mean pitch values have an excellent agreement with those measured by optical diffractometry. Nevertheless, irregularities of the gratings were only deduced from the SPM results. Finally, the usage of the 1D/2D gratings for the calibration of a typical SPM is illustrated.