Contrast Enhancement for Topographic Imaging in Confocal Laser Scanning Microscopy

Lena Schnitzler,Markus Finkeldey,Martin R Hofmann,Nils C Gerhardt

doi:10.3390/app9153086

Lena Schnitzler, Markus Finkeldey + Show 2 more

Open Access

https://doi.org/10.3390/app9153086

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Journal: Applied sciences	Publication Date: Jul 31, 2019
Citations: 3	License type: CC BY 4.0

Affiliation: Ruhr University Bochum

Abstract

The influence of the axial pinhole position in a confocal microscope in terms of the contrast of the image is analyzed. The pinhole displacement method is introduced which allows to increase the contrast for topographic imaging. To demonstrate this approach, the simulated data of a confocal setup as well as experimental data is shown. The simulated data is verified experimentally by a custom stage scanning reflective microscopy setup using a semiconductor test target with low contrast structures of sizes between 200 nm and 500 nm. With the introduced technique, we are able to achieve a contrast enhancement of up to 80% without loosing diffraction limited resolution. We do not add additional components to the setup, thus our concept is applicable for all types of confocal microscopes. Furthermore, we show the application of the contrast enhancement in imaging integrated circuits.

Highlights

The patent by Minsky in 1961 was the first step in the development of confocal laser scanning microscopy (CLSM) [1]
We show the effects of the contrast enhancement for two cases, a confocal system with ideal lenses and with a real lens
We presented a contrast enhancement method to improve the visualization of topographic structures in a confocal laser scanning microscope

Summary

Introduction

The patent by Minsky in 1961 was the first step in the development of confocal laser scanning microscopy (CLSM) [1]. One crucial part of the confocal microscope is the pinhole It enables optical sectioning, enhances the contrast and improves the lateral resolution [4,12]. In DCM the sample is defocused in such a way that its axial plane corresponds to a position on the linear slope of the axial intensity distribution This results in a high sensitivity to height changes and, after a calibration, an increase in measurement accuracy for these [25,26]. We show an easy to integrate method of contrast enhancement in reflection CLSM for topographic structures with low height differences and low contrast For this purpose, we apply an axial shift of the pinhole or the associated lens. Due to the contrast enhancement, even structures with low height variance can be observed and the flatness of a layer can be verified

Technique

Simulation

Test Chart and Application

Experiment

Findings

Discussion

Conclusions