Advancing the micromechanical characterization of silicon with a focus on high temperatures

Silicon is one of the defining materials of the current age. The deformation of silicon under load is of interest in several applications and processing techniques. Exemplarily, the room temperature deformation behavior is important in abrasive machining processes. The deformability at high temperatures is especially relevant for annealing processes where undesired plastification must be avoided to ensure device reliability and lithographic mask alignment. Additionally, silicon is readily available in high-quality single crystals and is therefore well-suited as a model material to study deformation mechanisms. An abundance of such mechanisms is triggered in silicon depending on the loading conditions. Studied here were pressure-driven phase transformations, twinning, and different types of dislocation plasticity. Accordingly, this thesis addresses several topics of academic and industrial interest. Indentation studies at room temperature delve into the low-temperature plasticity of silicon, which is dominated by a high-pressure phase transformation. They can lead to the formation of different metastable crystalline silicon phases or amorphous silicon. A better understanding of these transformations enables tailoring the unloading parameters to obtain transformed crystalline silicon of good quality and quantity, which can be further transformed to hexagonal silicon ¿ a promising substrate for integrating direct band gap semiconductors on silicon. The high temperature studies significantly expand the previously accessible temperature range for such small-scale experiments on silicon up to 950 °C. Three methods of assessing the high-temperature plasticity were applied: Nanoindentation with self-similar Berkovich tips, spherical nanoindentation, and uniaxial compression of micropillars. The spherical indentation experiments were applied to polycrystalline silicon thin films as the most suitable test to measure the flow behavior of such a structure. The self-similar indentation and uniaxial compression were used on monocrystalline substrates in a fashion where the experiments complement each other. Even at high temperatures, Berkovich indentation provides a reliable test that can be performed on a flat surface without elaborate sample preparation. Furthermore, it is comparably robust considering alignment and other contact deviations. However, the multiaxial loading makes the interpretation of the deformation behavior challenging. Here, uniaxial micropillar compression comes into play. The lithographically produced pillars are much more elaborate to produce, but provide the ability for more insightful interpretation and post-deformation microscopy. In total, the understanding of the deformation of microscopic volumes of silicon from ambient conditions up to 950 °C has been advanced by different micromechanical approaches.