Edge chipping minimisation strategy for milling of monocrystalline silicon: A molecular dynamics study

Direct patterning of functional microstructures on monocrystalline silicon by mechanical micro milling has drawn intense interests as an alternative to the conventional lithography techniques in microelectronics fabrication. Despite mechanical micro milling offering advantages such as high versatility and low operating cost, machining-induced defects such as edge chipping occur on the surface edges of a finished product, and it may affect its functionality. To address this challenge, a novel hybrid technique that combines mechanical machining and the deposition of a layered sacrificial structure on the silicon surface has been proposed to minimise the machining-induced edge chipping. In this paper, the feasibility and cutting mechanism of silicon under the proposed hybrid technique has been studied by molecular dynamics simulation. Underlying mechanisms such as material deformation, chip formation and stress behaviour are analysed. Reduction of the stress intensity and cutting forces were observed when silicon was machined under the proposed hybrid conditions. The effect is due to thermal softening, which resulted from the high cutting temperature and the interfacial stress between the copper and the silicon layers. Also, machining monocrystalline silicon by the proposed hybrid technique also showed desirable properties which include low subsurface damages, large material removal rate and better surface finishing (R_q < 0.1 nm).