Measurement of the roughness of supersmooth surfaces using a stylus instrument

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Abstract
Developments in a number of (engineering) industries have led to a requirement for supersmooth surfaces and for the ability to measure such surfaces. A number of different methods can be applied to measuring these surfaces, and a recent European Commission sponsored project has sought to provide a set of calibrated artefacts for the comparative assessment of different methods in measuring surfaces down to the order of 0.1 nm RMS roughness. The authors' involvement in this project was to develop a stylus instrument, using an inductive transducer, to measure the artefacts produced. The requirements were to produce an instrument having the attributes of fine resolution, low noise, and good repeatability. This paper outlines the architecture of the instrument (a prototype of the Nanostep 2), and the performance achieved. Some comparisons are given between the measurement of artefacts made with this instrument and other instrument types, notably an optical heterodyne profilometer (OHP). The results demonstrate that the instrument shows good agreement with the OHP, good repeatability, low noise (of the order of 0.2 nm RMS), and a resolution of the order of 0.3 nm.