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THE PURPOSE
In the race to produce integrated circuits of ever increasing complexity and decreasing size, the wavelengths used to write these circuits are becoming smaller and smaller. The mirrors used in next generation of Extreme UV Lithography (EUVL) projection systems must have a shape of unprecedented accuracy - this poses a significant challenge to metrologists. Complicated mirror shapes and low shape error tolerances require novel measurement techniques. Since scanning type profilometers and interferometers relying on reference- or auxiliary- optics generally carry unacceptable intrinsic errors, novel measurement devices must be developed.
This project constitutes the development of a 2D absolute interferometer, providing absolute optical path difference (OPD) measurements over a range of several mm, with an unprecedented accuracy of 0.1nm (Atomic Scale!).
EUV Mirror Substrate of the type to be measured with the interferometer
THE METHOD
The work is divided into two sections, Practical and Theoretical. The practical aspect of the thesis is the design, construction and testing of the interferometric setup, while the theoretical challenge is the development of an inverse propagation algorithm sufficiently stable to handle the desired accuracy as well as taking into account all relevant physical effects occurring at these scales.
The type of equipment being used includes stabilised as well as tuneable Lasers, Acousto-optic modulators, Fiber optics, CMOS optical sensors, piezo- and motor-driven nanopositioning devices, Counters, Synthesisers, Custom electronics, Vacuum chambers, vibration isolation, temperature stabilization, as well as the full range of passive optical devices found in a standard optics laboratory.
Photograph of the current setup located in the basement of the TN building.