Comparison of optical and stylus methods for measurement of surface texture

Optical methods are increasingly used for measurement of surface texture, particularly for areal measurements where the optical methods are generally faster. A new Working Group under Technical Committee (TC) 213 in the International Organization for Standardization is addressing standardization issues for areal surface texture measurement and characterization and has formed a project team to address issues posed by the optical methods. In this paper, we review the different methods of measuring surface texture and describe a classification scheme for them. We highlight optical methods and describe some of their characteristics as well as compare surface-profiling results obtained from three optical methods with those obtained from stylus profiler instruments. For moderately rough surfaces (Ra ≈ 500 nm), roughness measurements obtained with white light interferometric (WLI) microscopy, confocal microscopy, and the stylus method seem to provide close agreement on the same roughness samples. For surface roughness measurements in the 50 to 300 nm range of Ra, discrepancies between WLI and the stylus method are observed. In some cases the discrepancy is as large as about 75% of the value obtained with the stylus method. By contrast, the results for phase shifting interferometry over its expected range of application are in moderately good agreement with those of the stylus method.