Některé faktory, které ovlivňují přesnost měření povrchů interferenčním mikroskopem s nízkou koherencí

Some factors that affect the surface measurement accuracy of a low-coherence interference microscope

conference paper

en

Low-coherence interference microscopy (LCIM) is a powerful imaging high-accuracy technique for surface inspection and profiling. The principle of this technique is based on the interference of two waves with the use of incoherent light, usually of halogen lamp or superluminescent diode. One of its principal advantages is that both the image intensity and the image phase may be extracted from the output signal. The image phase may be converted subsequently into the surface height data. The image intensity is depth discriminated in a similar way as in the confocal microscopy. A limited lateral resolving power of the microscope significantly influences the accuracy of profiling with LCIM. This factor affects not only the image intensity of the reconstructed signal, but also behaviour of the image phase. It could result in an error in surface-height data measurement, especially if the structure contains details, the size of which is comparable with the resolving power of the microscope. This paper deals with the deviation of measurement of one-dimensional and two-dimensional periodic surface structures in relation to the numerical aperture of the objective lens and to the spectral composition of the illumination. The calculations are based on the polychromatic coherent transfer function, which describes the influence of temporal and spatial coherence of illumination on the imaging characteristics of the LCIM. Experiments were done with the reflected-light low-coherence holographic microscope

Interferenční mikroskop s nízkou koherencí (LCIM) je účinná zobrazovací technika pro inspekci a měření povrchů s vysokou přesností. Principem této techniky je interference dvou vln a použití nekoherentního světla, obvykle halogenové lampy či superluminiscenční diody. Principiální výhodou je fakt, že z výstupního signálu lze extrahovat jak obrazovou intenzitu, tak obrazovou fázi. Obraziovou fázi lze následně konvertovat na výškové údaje o povrchu vzorku. Obrazová intenzita je hloubkově diskriminována podobně, jako v konfokálním mikroskopu. Omezená příčná rozlišovací schopnost mikroskopu podstatně ovlivňuje přesnost měření povrchů pomocí LCIM. Tento faktor ovlivňuje nejen obrazovou intenzitu, ale také obrazovou fázi. Výsledkem může být chyba měření profilu výšky povrchu, zvláště v případě, kdy povrch obsahuje detaily, jejichž velikost je srovnatelná s rozlišovací schopností mikroskopu. Tento článek se zabývá odchylkou měření 1D a 2D periodických povrchových struktur vzhledem k numerické apertuře objektivu a spektrálnímu průběhu osvětlení. Výpočty jsou založeny na polychromatické koherentní funkci přenosu, která popisuje vliv časové i prostorové koherence osvětlení na obrazové charakteristiky LCIM. Experimenty byly provedeny na LCIM v konfiguraci pro odražené světlo.

Low-coherence interference microscopy (LCIM) is a powerful imaging high-accuracy technique for surface inspection and profiling. The principle of this technique is based on the interference of two waves with the use of incoherent light, usually of halogen lamp or superluminescent diode. One of its principal advantages is that both the image intensity and the image phase may be extracted from the output signal. The image phase may be converted subsequently into the surface height data. The image intensity is depth discriminated in a similar way as in the confocal microscopy. A limited lateral resolving power of the microscope significantly influences the accuracy of profiling with LCIM. This factor affects not only the image intensity of the reconstructed signal, but also behaviour of the image phase. It could result in an error in surface-height data measurement, especially if the structure contains details, the size of which is comparable with the resolving power of the microscope. This paper deals with the deviation of measurement of one-dimensional and two-dimensional periodic surface structures in relation to the numerical aperture of the objective lens and to the spectral composition of the illumination. The calculations are based on the polychromatic coherent transfer function, which describes the influence of temporal and spatial coherence of illumination on the imaging characteristics of the LCIM. Experiments were done with the reflected-light low-coherence holographic microscope

low-coherence interference microscopy, holographic microscopy, optical sectioning, spectral composition, lateral resolving power

12.04.2007

SPIE-The International Society for Optical Engineering

Bellingham, USA

978-08-1946-748-5

15th Czech-Polish-Slovak Conference on Wave and Quantum Aspects of Contemporary Optics

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