Calibration of a 2D reference mirror system of a photomask measuring instrument

Felix Meli; Nicolas Jeanmonod; Christian Thiess; Rudolf Thalmann

doi:10.1117/12.445625

22 October 2001 Calibration of a 2D reference mirror system of a photomask measuring instrument

Felix Meli, Nicolas Jeanmonod, Christian Thiess, Rudolf Thalmann

Proceedings Volume 4401, Recent Developments in Traceable Dimensional Measurements; (2001) https://doi.org/10.1117/12.445625
Event: Lasers in Metrology and Art Conservation, 2001, Munich, Germany

Abstract

A photomask measuring instrument was developed and built at METAS. The instrument consists of an air bearing x-y stage for the positioning of the mask with a range of 400 mm by 300 mm, a digital video microscope system for the localization of the structures and a differential two axis plane mirror interferometer. The interferometric measurements are made with respect to an x-y reference mirror system made out of Zerodur. The uncertainty for 2D measurements is directly influenced by the shape of the reference system i.e. by the straightness and orthogonality of the mirrors. Through a precise characterization of the reference system its imperfections can be corrected numerically. An initial determination of the mirror shape was performed on a straightness measurement instrument consisting of a granite beam with an air bearing carriage and an inductive touch probe system. The method delivered initial flatness data with a high positional resolution but with some low order distortion due to a circular bending of the used granite beam which was induced by small temperature gradients. An in-situ calibration of the reference system on the photomask measuring instrument itself was used to improve these initial measurements. This second calibration was made by measurements of a 400 mm quartz line scale in axial and in two diagonal directions. By numerical simulation of these measurements of the x- and y- mirror shapes and the angle between the mirrors were determined. Circular and sinusoidal functions were used for the additional mirror form corrections, which were up to 40 nm for the y-axis and up to 140 nm for the x-axis. A final verification measurement showed that the agreement between the axial and the diagonal line scale measurements is now better than 10 nm.

Citation Download Citation

Felix Meli, Nicolas Jeanmonod, Christian Thiess, and Rudolf Thalmann "Calibration of a 2D reference mirror system of a photomask measuring instrument", Proc. SPIE 4401, Recent Developments in Traceable Dimensional Measurements, (22 October 2001); https://doi.org/10.1117/12.445625

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