Abstract
Although optical 3D topography measurement instruments are widespread, measured profiles suffer from systematic deviations occurring due to the wave characteristics of light. These deviations can be analyzed by numerical simulations. We present a 3D modeling of the image formation of confocal microscopes. For this, the light-surface interaction is simulated using two different rigorous methods, the finite element method and the rigorous coupled-wave analysis. The image formation in the confocal microscope is simulated using a Fourier optics approach. The model provides high accuracy and advantages with respect to the computational effort as a full 3D model is applied to 2D structures and the lateral scanning process of the confocal microscope is considered without repeating the time consuming rigorous simulation of the scattering process. The accuracy of the model is proved considering different deterministic surface structures, which usually cause strong systematic deviations in measurement results. Further, the influences of apodization and a finite pinhole size are demonstrated.
Highlights
Since the size of electrical and optical components is continuously decreasing, the demand for accurate measurement technology increases in order to ensure high quality
We present a 3D simulation model for confocal microscopy and use this model to study the transfer characteristics of confocal microscopes with regard to 2D surface structures including edges, curvature and steep slopes
Measurement results obtained at these types of deterministic surface structures and their theoretical replication are of high interest for manufacturers and users of confocal scanning microscopy (CSM) instruments
Summary
Since the size of electrical and optical components is continuously decreasing, the demand for accurate measurement technology increases in order to ensure high quality. CSM uses (partially) spatially coherent illumination, whereby interference effects in the scattering process of the incident beam with the measurement object are enhanced For these reasons a numerical model enabling a comparison of the accuracy of optical profilers with respect to certain surface profiles without the need for performing measurements is of high interest for manufactures, scientists and industry. In order to underline the reliability of our model, we show reconstructed surface topographies obtained by simulations and compare them to measurement results In this context, the influences of varying pupil functions and a finite pinhole size are discussed with respect to measurement objects providing large spatial frequencies. Aberrations could be applied in the model analogously to the work of Rahlves et al [14]
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