Comparison of optical surface roughness measured by stylus profiler, AFM, and white light interferometer using power spectral density

Surface roughness measurements were performed on fused-silica, silicon wafer, and glass-ceramic (Zerodur) by mechanical stylus profiler, atomic force microscope (AFM), and white light interferometer (WLI). Because of the differences of spatial frequency bandwidth of the measurement instruments surface roughnesses are actually not directly comparable. In this study, a novel method has been developed to directly compare the roughnesses measured with different instruments using power spectral density (PSD) function which can be calculated from the measurement data. The RMS roughnesses were obtained by integrating areas in the overlapping regions of two or more instruments so that roughnesses measured with different instruments could be directly compared. The agreement among RMS roughnesses measured with the different techniques improved considerably, and the remaining differences could be explained as being caused by surface features to which the instruments responded differently. This fruitful work also provides a great guidance for the selection of surface roughness measurement instruments.