Comparison of Optical and Stylus Methods for Measurement of Surface Texture

T.V. Vorburger, H.-G. Rhee, T.B. Renegar, J.-F. Song, L. Ma, E. Whitenton, A. Zheng
National Institute of Standards and Technology, Gaithersburg, MD 20899 USA

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 we describe a classification scheme for them. We then highlight optical methods and describe some of their characteristics. We compare surface profiling results obtained with several optical methods with those obtained with the stylus method. For moderately rough surfaces (Ra ~ 500 nm) roughness measurements obtained with white light interferometric microscopy (IM), confocal microscopy, and the stylus method seem to provide close agreement on the same roughness samples. For surface roughness measurements in the 50 nm to 300 nm range of Ra, discrepancies between white-light interferometry and the stylus method are observed. In some cases the discrepancy is as large as 80 % of the value obtained with the stylus method. Reasons for this are suggested. By contrast, the results for phase shifting interferometry over its expected range of application (Ra  about 150 nm) are essentially in good agreement with those of the stylus technique.

Keywords

surface, metrology, stylus, interferometric, microscopy, confocal, white light, optical, texture, finish