Microscopic stress analysis of nanoscratch induced sub-surface damage in a single-crystal silicon wafer

The existing stress criterion assumes the material to be isotropic and only distinguishes elastic, plastic and crack zones to explain the scratching-induced sub-surface damage (SSD) during the contact loading processes such as nanoindentation, nanoscratching and grinding. However, anisotropic single-crystal materials such as monocrystalline silicon and silicon carbide have more diverse defect characteristics and SSD in these materials cannot be well explained and predicted using the existing criterion. In this study, a thorough microscopic characterisation and complementary stress analysis were performed on a single-crystal silicon wafer during nanoscratching. A novel criterion based on mechanism of dislocation multiplication and propagation was proposed and validated, providing a better understanding of SSD prediction in silicon. Compared to conventional SSD models, this new shear stress-based criterion can accurately predict the position and extent of dislocations in silicon. The dislocations layout for scratching along any direction on the (100) surface of Si were further discussed to offer a comprehensive understanding of the effect of anisotropic structure of single-crystals on the SSD. The improved understanding of inelastic deformation in single-crystal silicon, which was revealed by this new model, will have a significant impact on the nanomanufacturing sector by guiding the contact mode experiments (grinding, indentation, machining) towards efficient machining.