Fundamental aspects of resolution and precision in vertical scanning white-light interferometry. (4th March 2016)

• Record Type: Journal Article
• Authors: Lehmann, Peter; Tereschenko, Stanislav; Xie, Weichang
• Is Part Of: Surface topography. Volume 4:Number 2(2016:Apr./Jun.)
• Publication Date: 2016-03-04
• Subjects: height and lateral resolution in SWLI -- batwing effect -- scanning white-light interferometry (SWLI) -- phase-shifting interferometry (SPI) -- interferometric slope effect -- envelope and phase evaluation -- nonlinear envelope filtering; Surfaces (Physics) -- Periodicals; Surfaces (Physics) -- Measurement -- Periodicals; 530.417
• DOI: 10.1088/2051-672X/4/2/024004
• Languages: English
• ISSNs: 2051-672X

Abstract

Abstract: We discuss the height and lateral resolution that can be achieved in vertical scanning white-light interferometry (SWLI). With respect to interferometric height resolution, phase-shifting interferometry (PSI) is assumed to provide the highest accuracy. However, if the noise dependence of SWLI phase evaluation and PSI algorithms is considered, SWLI measurements can be shown to be more precise. With respect to lateral resolution, the determination of the coherence peak position of SWLI signals seems to lead to better results compared to phase based-interferometric measurements. This can be attributed to the well-known batwing effect. Since batwing is a nonlinear effect applying nonlinear filters, e.g. a median filter, it reduces them significantly. If filtering is applied prior to the fringe order determination and phase evaluation, the number of artefacts known as ghost steps can be eliminated without changing the modulus of the phase. Finally, we discuss the dependence of measured height values on surface slope. We show that in interference microscopy there are additional limitations which are more rigid compared to the maximum surface slope angle resulting from the numerical aperture of the objective lens. As a consequence, the measurement precision breaks down at slope changes of steeper flanks even if the modulation depth of the interference signals is still good enough for signal analysis.