Lens aberration compensation in interference microscopy

Su, Rong; Thomas, Melanie; Li, Mingyu; Drs, Jakub; Bellouard, Yves; Pruß, Christof; Coupland, John N.; Leach, Richard

doi:10.1016/j.optlaseng.2020.106015

Cited by 40 publications

(29 citation statements)

References 33 publications

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“…This is confirmed by the experimentally measured 3-D surface transfer function of the same instrument configuration seen in Ref. 31. Due to the design of the objective lens, the polarization of illumination incident on the surface is nominally circular, with a small radial component resulting from the high NA of the objective lens.…”

Section: Methodssupporting

confidence: 72%

“…In addition, this effect is partially caused by the imperfect transfer function of the instrument due to optical aberration and apodization due to the reference mirror in its Mirau objective. 29,31 In Figs. 7 and 8, comparison is made using a sinusoidal grating with higher amplitude and longer wavelength, as specified in Table 1.…”

Section: Resultsmentioning

confidence: 98%

“…25,26 The foil model can provide the CSI signal from a surface so long as the Kirchhoff approximation is satisfied, and the model is currently being used to predict the effects of reference mirror defocus, 27 provide new methods of instrument calibration, 28 characterize resolution from measurements of microspheres, 29 correct measured transfer characteristics, 30 and allow for lens aberration compensation in CSI. 31 The foil model also assumes that multiple scattering is negligible. 26 Despite the mitigating effect of a finite spatial frequency bandwidth, the effect of multiple scattering and loss of diffraction orders cannot be neglected and remains a problem for surfaces that are rough at the optical scale, or when coherent features such as vee-grooves or sharp edges are present.…”

Section: Introductionmentioning

confidence: 99%

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Modeling of interference microscopy beyond the linear regime

Thomas

Nikolaev

et al. 2020

Opt. Eng.

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Coherence scanning interferometry (CSI), a type of interference microscopy, has found broad applications in the advanced manufacturing industry, providing high-accuracy surface topography measurement. Enhancement of the metrological capability of CSI for complex surfaces, such as those featuring high slopes and spatial frequencies and high aspect-ratio structures, requires advances in modeling of CSI. However, current linear CSI models relying on approximate surface scattering models cannot accurately predict the instrument response for surfaces with complex geometries that cause multiple scattering. A boundary elements method is used as a rigorous scattering model to calculate the scattered field at a distant boundary. Then, the CSI signal is calculated by considering the holographic recording and reconstruction of the scattered field. Through this approach, the optical response of a CSI system can be predicted for almost any arbitrary surface geometry. © The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

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Section: Methodssupporting

confidence: 72%

Section: Resultsmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

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Modeling of interference microscopy beyond the linear regime

Thomas

Nikolaev

et al. 2020

Opt. Eng.

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“…From the 0° results shown in Figure 5(a), the grating's blazed profile is shown, however, the PV heights across the profile are approximately 0.12 µm, below the 0.2 µm PV height measured by the AFM instrument. This reduction in height is expected and occurs due to the spatial frequency transfer characteristics of the CSI instrument [27][28][29]23 , with a transmission magnitude at 0.3 µm -1 of approximately 70% 24 . Further reductions to the transmittance are expected as the instrument will have had some reference mirror defocus present while the measurements were taken 30 .…”

Section: Resultsmentioning

confidence: 87%

“…We use a Zygo Nexview™ NX2 CSI instrument with objective lenses outlined in Table 1 for the measurements presented in this paper. A detailed description of the working principle of CSI 22 and recent studies on its 3D transfer function can be found elsewhere 23,24 .…”

Section: Csi Instrumentmentioning

confidence: 99%

Optical topography measurement of steeply-sloped surfaces beyond the specular numerical aperture limit

Thomas

Su²,

Groot³

et al. 2020

Optics and Photonics for Advanced Dimensional Metrology

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Engineered functional surfaces often feature varying slopes on macro-and micro-scales. When surfaces are mirror-like, the highest surface slope that can be measured by a far-field 3D imaging optical surface measuring instrument is the arcsine of the numerical aperture (NA) of the objective lens, i.e. the acceptance angle of the lens. However, progress in instrument design has allowed for measurement of non-specular surfaces with slopes steeper than this "traditional" NA limit. Nonetheless, there is currently a lack of understanding about the instrument response to surfaces with steep slopes beyond this limit. It is unclear over what surface spatial frequencies we can expect to accurately report fine surface-feature details.Here we present results demonstrating the capability of a commercial coherence scanning interferometer for measuring surface topography of a roughened flat and a blazed grating with tilt angles greater than the NA slope limit. We show that the surface form, i.e. the tilted plane, can be measured correctly. But, while surface texture information that can appear useful is also obtained, tilting significantly influences the measurement accuracy of micro-scale texture, and for asymmetric gratings, can depend on the tilting direction. A simplified surface scattering model suggests that the loss of scattered power captured by the instrument and a low signal-to-noise ratio causes the reduction of measurement accuracy. However, a rigorous three-dimensional instrument model is needed for a full understanding; we will develop this in our future work.

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Gaussian process regression‐based detection and correction of disturbances in surface topography measurements

Maculotti

Genta

Quagliotti

et al. 2021

Quality & Reliability Eng

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Modern smart and intelligent manufacturing is characterised by an increasing use of highly engineered surfaces and quasi‐free form geometries, for example, by additive manufacturing, and the requirement for fast and informative measurement tools for quality controls in production. These have lately pulled towards the adoption of optical surface topography measuring instruments to qualify technological surfaces, which are core to being assessed to characterise the product and optimise the manufacturing process. Surface topography measurements performed by optical instruments are known to suffer from disturbances, such as non‐measured points and spikes. These are due to complex interactions between the measurand and the instrument and may result in poor measurement quality and biased characterisation results. Currently, the correction of measurement disturbances is carried out by empirical approaches which mostly involve thresholding and interpolations, whose sensitivity is often devolved to the operator. In this work, a Gaussian process regression‐based approach is outlined to identify and correct measurement disturbances exploiting spatial correlation properties of the measurements to provide a formal, robust, and univocally defined approach to manage measurement disturbances. The proposed approach, differently from currently available alternatives, is capable of managing at once the different type of disturbances by means of a supervised machine learning technique. The formal and practical advantages of the proposed method are discussed exploiting case studies of industrial interest applied on quasi‐flat surfaces to stress the disturbances effect.

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Lens aberration compensation in interference microscopy

Cited by 40 publications

References 33 publications

Modeling of interference microscopy beyond the linear regime

Modeling of interference microscopy beyond the linear regime

Optical topography measurement of steeply-sloped surfaces beyond the specular numerical aperture limit

Gaussian process regression‐based detection and correction of disturbances in surface topography measurements

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