Experimental–numerical analysis of silicon micro-scratching

Abstract

The continuous decrease in feature size in the production of electronic chips has two major consequences for silicon wafers: (i) processing conditions for slicing and grinding operations need to be optimized and (ii) surface damage imposed by wafer handling and transport needs to be minimized. Cultivating a deeper understanding of the subsurface implications of contact, in particular during scratching, is necessary to achieve these goals. The active subsurface micro-deformation mechanisms, including phase transformations and crack formation, can only be measured post-scratch. On the other hand, numerical models are free of experimental constraints and can therefore serve an instrumental role in uncovering the active deformation mechanisms during scratching. However, model identification and validation with experimental data is essential for reliable simulation results. Therefore, in this paper, a numerical scratch model consisting of a continuum particle methodology combined with a large strain inelastic constitutive model is exploited, whereby the parameters are identified from indentation data. The numerical–experimental results are next compared for a range of micro-scratch tests. The experimental micro-scratch device was mounted inside a scanning electron microscope to perform in situ scratch experiments. The real-time observations at the scratched surface allowed to assess and exclude possible experimental artifacts. The simulations demonstrate the ability to investigate the evolution of the phase transformations underneath the scratched surface and relate this to the hydrostatic pressure. Notably, at the simulated subsurface phase boundary, hydrostatic tension was found which is expected to play an important role in median crack formation, as often reported in the literature. For the simulation and experiments, the steady-state segments are compared and it was found that the model accurately reproduces the substantial surface recovery due to the Si-II → Si-a phase transformation. Additionally, the simulated and experimental surface cross-sectional profiles for normal scratching loads of 30, 40 and 50 mN are in adequate agreement.