Development of a sinusoidal chirp material measure for the characterization of optical surface topography measuring instruments

Optical surface topography measuring instruments are used more and more widely for surface quality control in industry by enabling fast, areal and non-destructive surface topography measurements. However, due to the complexity of the interaction between the surface properties to be measured and the measuring system, their capability to accurately reproduce topographical features of a surface under test is quite often questionable. To understand and investigate the topographic measurement accuracy of different optical surface topography measuring instruments, a physical measurement standard has been developed at PTB which is intended to be used to determine the metrological characteristics of surface topography measuring instruments such as topographic spatial resolution and topography fidelity. The physical standard, fabricated by a diamond turning process, containing nine sinusoidal structures with different amplitudes from 50 nm to 10 mu m and varying spatial wavelengths from 2.6 mu m to 82.8 mu m, is suitable for the characterization of optical instruments with different magnification and numerical apertures. The design of the chirp structures, including the wavelength series, the smallest wavelength for different amplitudes, the slope distribution and the layout are detailed in this paper. The tool path for accurately positioning the cutting tool in fabrication is also described. First measurement results of the instruments response in terms of the features' aspect ratio, slopes and curvatures, the homogeneity of the field of view of a confocal microscope are presented.