Accurate and traceable calibration of one-dimensional gratings

TLDR

Accurate and traceable calibration of lateral standards (1D and 2D gratings) is essential for nano‑ and microtechnology, yet optical diffractometers can only measure mean pitch and not uniformity. The study aims to calibrate 1D gratings with a large‑range scanning probe microscope and to demonstrate their use for calibrating a typical SPM. The authors employ the microscope with optimized strategies, using gravity‑centre and Fourier‑transform data‑evaluation methods, correcting cosine error, and calibrating several 1D gratings. The calibrated mean pitch values agree excellently with optical diffractometry, while irregularities are revealed only through the SPM measurements.

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.