A novel material measure for characterising two-dimensional instrument transfer functions of areal surface topography measuring instruments

Abstract

A new material measure for characterising two-dimensional (2D) instrument transfer functions (ITF) of areal surface topography measuring instruments has been designed, manufactured, calibrated and applied. Several innovative ideas are implemented in its design. Firstly, the material measure is designed with circular structure patterns. Such rotational symmetric patterns are advantageous for characterising the ITF in different angular directions, thus for characterising angular-dependent asymmetries of instruments. Secondly, different types of patterns are designed: circular chirp (CC) pattern and circular discreate grating (CDG) pattern. They represent different kinds of spatial signals applicable for characterising ITFs. A material measure consists of 25 different circular patterns with radii from 30 μm to 300 μm, and wavelengths from 0.1 μm to 150 μm. These patterns can be applied complementary and combinedly, offering high application flexibility for calibrating a variety of instruments, e.g. with different optical objectives from 5× to 100× and with different sizes of field of view (FOV). Material measures with heights of 8 nm, 16 nm and 32 nm, respectively, have been manufactured using state-of-the-art e-beam lithography technique. The feature heights are far less than λ/4, thus they are suitable for characterising the ITF of optical tools which can be approximated as linear systems. A metrological large range atomic force microscope (AFM) has been applied in the calibration of the developed material measure, showing good feature quality. The calibrated material measure has been successfully applied in research and industry.