dc.description.abstract
Polymer materials are used in a vast range of applications. Aside from comparably trivial applications that are surrounding our daily lives, i.e., as construction or packaging materials, polymers are employed in highly demanding fields, where their properties must be thoroughly tuned and optimized to fulfill the intended purpose. Such an application field is the semiconductor industry, where polymer films are used as coating, insulation, or encapsulation materials. As semiconductor devices must be operable in ambient conditions, polymer coatings are utilized to protect sensitive components from environmental influences such as temperature, humidity, and corrosive gases (e.g., H2S, SO2). The development of such materials with enhanced properties requires testing equipment for exposure to controlled environmental conditions, as well as analysis techniques and methods for investigating the effects that the exposure causes on the investigated materials.This work aimed to develop a weathering setup for sample exposure to harsh environments at defined temperatures, relative humidity, and corrosive gas concentration, as well as suitable LA-ICP-MS and LIBS methods for advanced sample characterization. The weathering experiments result in the degradation of the tested polymers and the uptake of the gases present in the testing atmosphere. For a successful investigation of the effects of weathering experiments in different conditions on thin polymer films, several requirements must be accounted for in the development of the analytical methods. Weathering tests of polymers with corrosive gases in a ppm concentration range only lead to low concentration increases within the polymers over reasonable weathering durations. Since non-metals, such as sulfur, pose a challenging task in elemental analysis, a thorough optimization for maximum sensitivity is required for a comprehensive analysis. In addition, high depth resolution is required to reveal differences in the gas uptake within the uppermost few micrometers of polymer films and the impact of different environmental conditions. Thus, laser parameters must be fine-tuned to achieve a suitable compromise between the depth resolution and sensitivity of the method. The measurement of depth profiles from samples weathered with H2S or SO2 reflects the uptake characteristic and, thereby, the protection capability of the investigated materials. Further, since LA-ICP-MS signals are influenced by the sample matrix, a comparison between different materials is only possible when quantitative results are provided. Followingly, a suitable quantification approach for sulfur in polymer thin films via LA-ICP-MS must be developed and implemented. Finally, the effect of polymer aging on the behavior in weathering experiments should be investigated. To detect potential UV-induced polymer oxidation while allowing spatial correlation with sulfur results, a simultaneous LA-ICP-MS & LIBS measurement setup is needed, including optimizing the experiment-specific sensitivity and depth resolution requirements. Overall, experiments were performed on in-house prepared polymer films for representative model systems (e.g., polyimide, polystyrene, polyvinylpyrrolidone, polyvinylacetate), as well as state-of-the-art protection coatings from our industrial partners. This thesis contains three manuscripts, two published in peer-reviewed scientific journals and one submitted, tackling the challenges described above and enabling the comprehensive investigation of polymers weathered in harsh corrosive environments:• Development of a new quantification approach for LA-ICP-MS: To quantitatively determine the sulfur uptake of polymers resulting from weathering experiments with varying temperature, humidity, and H2S or SO2 concentration with LA-ICP-MS, a new calibration approach was developed based on standard addition via spray deposition of liquid standards. The developed approach was verified for sulfur via a reference determination and brings significant benefits compared to the more conventional Dried Droplet approach in terms of analysis time and reusability of prepared standards for multiple analyses. In feasibility experiments, it was further demonstrated that the approach is versatile and has the potential for multielement analysis for other material types and elements.•Simultaneous LA-ICP-MS & LIBS for determining UV-induced polymer oxidation and the influence on weathering effects: Polymer aging was simulated by UV exposure in the ambient atmosphere. A combined LA-ICP-MS & LIBS setup was developed and separately optimized for mapping and depth profiling applications to investigate the influence on the gas uptake characteristics and polymer oxidation. LA-ICP-MS signals were evaluated for the sensitive determination of sulfur. LIBS was employed to analyze degradation-specific changes of the polymers since aside from non-metals (H, O, N, C), molecular fragments (C2, CN) can be measured with this technique. Thereby, it could be shown that polymer films exposed to a UV treatment show an increase of measured oxygen signals in surface near regions, indicating oxidation, which significantly impacts the H2S / SO2 uptake characteristic of respective materials in weathering experiments. Compared to state-of-the-art literature, the achieved spatial resolution (40 μm for laterally resolved polymer discrimination, 150 – 360 nm for depth-resolved sulfur and oxygen determination) could be significantly improved.•Implementation of a procedure for testing polymers in harsh corrosive environments: This work describes the developed weathering setup combined with quantitative LA-ICP-MS analysis of sulfur as a testing procedure for polymer interaction in harsh environments. Systematically, the influence of the gas type (H2S / SO2), the temperature (20 – 80 °C), and relative humidity (0 – 80 %) are investigated in repeated weathering experiments for four polymer types (polyimide, polyvinylpyrrolidone, polystyrene, polyvinylacetate). Quantitative sulfur bulk results and depth profiles with 120 – 360 nm depth resolution reveal significant differences between the polymer types and the effect of temperature and humidity. The demonstrated testing and analysis approach is a perfect tool for the corresponding material development of barrier coatings since it allows testing the impact of changing material composition on the barrier performance.The tools and methods developed in the scope of this thesis represent an extension to the currently published literature regarding polymer analysis, bringing some specific advantages compared to the state-of-the-art. The methodologic approaches proven in this thesis can be adapted and applied to other materials and questions and thus can benefit other researchers in the future.
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