Indirect geometry measurement method based on confocal microscopy and fluorescent microparticles

Abstract

The precise production of micro- or micro-structured components of increasingly different materials requires ever more precise and flexibly adjustable geometry measurement methods. Today’s optical metrology offers various innovative approaches for this purpose. A major shortcoming is, however, that not all surfaces and structures to be measured are optically cooperative and return too little light or information to the measurement system for the signal analysis. Therefore, indirect optical geometry measurements are introduced as a new approach: Instead of directly detecting the outer boundary layer of the measuring object, the shape of the object’s imprint in the surrounding medium is examined. For this purpose, the surrounding medium is enriched with fluorescent substances and a confocal microscope scans the space surrounding the measured object. The spanned area above which the fluorescence signal disappears is then determined as the boundary layer between the measurement object and the surrounding medium. As a result, the object geometry is obtained completely independently of the optical response behavior of the object. While first realizations studied measurements in a liquid environment, this work demonstrates for the first time the feasibility of indirect optical geometry measurements in air environments with the aid of fluorescent microparticles. In order to maximize the measurement accuracy, different model-based signal evaluation approaches for determining the interface geometry from the fluorescence signals are investigated and compared, taking both cases (liquid and air environment) into account. Finally, indirect optical measurements are performed on a step geometry, reconstructing the height profiles using the theoretically derived model function.