Micro-machined substrates for high-throughput characterization of stress in thin films

Lars Banko, Ruhr-Universität Bochum, Bochum, Germany
Dario Grochla, Ruhr-Universität Bochum, Bochum, Germany
Alfred Ludwig, Ruhr-Universität Bochum, Bochum, Germany

Combinatorial material science enables fast innovation cycles in the search for new functional materials and the optimization of existing material systems. The success of combinatorial investigations grounds on efficient screening methods for the desired materials properties that are applied to compositional spread materials libraries. Mechanical stress measurement are subject to many publications in a variety of materials classes as the residual stress can be linked to several materials and system properties (e.g. mechanical, optical, structural, tribological). The control of the residual stress during synthesis provides opportunities to optimize materials for their designated application. Stress measurements can be challenging since different boundary conditions limit the choice of methods. A versatile method to determine the stress during and after film growth is the curvature method, which allows for a calculation of the stress by measuring the curvature of a film-substrate-combination. Available standard substrates like Si-wafers are geometrically limited in shape and thickness which prohibits spatial resolved measurements. In order to overcome these challenges micro-machined Si-based substrates were developed that can be applied to perform stress measurements on combinatorial materials libraries. In combination with automated high-throughput test stands efficient screenings of stresses can be realized in situ during film growth and processing. The development of different substrates resulted in a versatile applicable stress sensor that can be easily applied in material science and industrial quality control of thin coatings.

In this work several application cases are demonstrated including in situ stress measurements during the growth of quasi-binary Al-Cr-N materials libraries, the measurement of reversible phase transformations and stress measurements of thin (<100 nm) and ultra-thin coatings (<10 nm).

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