Towards a continuous frequency band chirp material measure for surface topography measuring instrument calibration
To experimentally determine the transfer behavior and the resolution limits of areal surface topography measuring instruments, numerous approaches have been suggested with the two most common ones being based on either rectangular (type ASG material measure) or sinusoidal (chirp material measure) test geometries, imaging various spatial frequencies. Each of the methods carries individual advantages and disadvantages. Here, we describe the design of a varied chirp material measure which provides sufficient amplitudes throughout a broad range of spatial frequencies. For its evaluation, two different approaches based on either geometrical fitting or a direct analysis in the frequency domain are described and compared with each other. The material measure provides a steady spectrum in the spatial frequency domain that can be evaluated with both approaches. Their advantages and disadvantages are composed to derive information for a reliable implementation that leads to a standardized evaluation routine with small uncertainty. The examination of the two methods results in an evaluation with a high statistical reliability that allows an unambiguous determination of the spatial transfer behavior.