PhD Thesis – Information and Computer Engineering

In September 2018 I finished my doctoral thesis in Information and Computer Engineering at the Institute of Technical Informatics of the TU Graz. I put the abstract here onto that page, so anyone might get an imagination what my thesis and work [1] was about.

Within that thesis several scientific contributions at conferences and journals were made.


Optical high-precision measurement devices are recommended for processes which require precise and automatic handling or measuring of touch-sensitive parts or assemblies. Contact-less measurement systems are particularly suitable for in-situ integration because in contrast to other measurement techniques, the measurement object itself is not influenced by the measurement process. Optical measurement systems are used in many different applications nowadays, like for example at the wafer production process in the semiconductor industry, where the identification of few micro-meter sized wafer-edge defects, as well as a highly precise wafer-handling is necessary.

The central research topic of this thesis is the determination of an object edge position in a 2D measurement plane. This should be done with sub-micrometer accuracy and high measurement rate at the same time. To satisfy the requirements the necessary system components like light sources, sensors, analog and digital signal processing as well as the modelling of the optical path, are considered within the scope of this work.

The used measurement principle relies on multiple exposure of the object edge onto a light sensitive detector. The exposure data is analyzed in order to find the position of the projection edges on the sensor. Furthermore, the projected edges are used for the fusion of the redundant measuring data information to infer an 2D edge position (X/Y) in the measurement plane. This edge position information can be used to measure geometrical object quantities like e.g. diameter or thickness, or as well qualify one objects edge condition. In an envisaged application, broken or chipped wafer edges could be detected as well as qualitatively assessed in their size.

To assess the measurement accuracy qualitatively, it is necessary to understand all the different sorts of error sources and occurring effects in this measurement setup. Thereby not just only the light source type, its imaging properties and the resulting modelling of the optical path play an important role. Moreover, it is necessary that possible sources of error are considered in the design and development phase of the complete measurement device.

Altogether, this thesis can be seen as a highly interdisciplinary research project, where through the period of several years, continuous research and ongoing development lead to a functional measurement system, which actually nearly satisfies all requirements. At the time when finishing this thesis, one measurement device is being integrated by one semiconductor manufacturer for testing purposes.

[1] Christian Mentin,  Development and Evaluation of Novel Techniques Enabling Accurate Edge Position Prediction in a High Precision 2D Laser Measurement System, Graz University of Technology, 2018.

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