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Limitations and innovations in scanning white light interferometry.

Lobera, J*; Gao, F*; Coupland, J*; Leach, R K (2008) Limitations and innovations in scanning white light interferometry. In: euspen 2008, 18-22 May 2008, Zurich.

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Abstract

Scanning white light interferometry (SWLI) is fast becoming one of the most popular methods for measuring surface topography in industry. When interpreting SWLI measurements, however, one must take due care as fundamental limitations of the methods used to reconstruct surface profile can, in certain circumstances, lead to unexpected results. Step height and grating artefacts have been used to investigate a number of commercial SWLI instruments and our findings form the basis of a good practice guide that will address the use of SWLI instrumentation and the interpretation of data. In this paper we will discuss our measurements and the mechanisms that are responsible for the observed errors. We show that systematic errors are prevalent in areas of large surface gradient and at step continuities and these typically correspond to misclassifications of fringe order. It is well known that dispersion in the objective lens is a major factor in precipitating errors of this kind. In this paper however, we also consider the effects of multiple scattering and show that this is often responsible for spurious artefacts in measured data. We show how errors due to multiple scattering can be identified and trapped in SWLI data and how they can be explained by a model of the scattering process. Finally we will describe how inverse modelling can be used to correct these errors and in some cases identify surface characteristics that would be overlooked by current SWLI instrumentation. For example, it will be shown that some information concerning features such as the vertical sidewalls of step artefacts and even undercut structures is present in SWLI data and can be retrieved in certain circumstances.

Item Type: Conference or Workshop Item (UNSPECIFIED)
Subjects: Engineering Measurements
Engineering Measurements > Dimensional
Last Modified: 02 Feb 2018 13:15
URI: http://eprintspublications.npl.co.uk/id/eprint/4149

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