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Molecular dynamics simulations of the nanometric cutting of single-crystal copper were performed with the embedded atom method. The nature of material removal, chip formation, material defects and frictional forces were simulated. Nanometric cutting was found to comprise two steps: material removal as the tool machines the top surface, followed by relaxation of the work material to a low defect configuration, after the tool or abrasive particle has passed over the machined region. During nanometric cutting there is a local region of higher temperature and stress below the tool, for large cutting speeds. Relaxation anneals this excess energy and leads to lower dislocation work material. At high cutting speeds (180 m s −1 ), the machined surface is rough but the work material is dislocation free after the large excess energy has annealed the work material. At lower cutting speeds (1.8-18 m s −1 ), the machined surface is smooth, with dislocations remaining in the substrate, and there is only a small excess temperature in the work material after machining. The size of the chip grows with increasing cutting speed.

INTRODUCTIONAmong the newly developed planarization technologies for ultra-large-scale integration metallization, chemical-mechanical planarization (CMP) has emerged to be most promising because it can provide better local and global planarization of the wafer surface. 3 In recent years, CMP has emerged as an enabling technology for the next generation of chip manufacturing and has become the second fastest growing area of semiconductor-equipment manufacturing. Beside interlayer-dielectric planarization, CMP has also found applications in shallow-trench isolation, damascene technologies, 4,5 and other novel processing techniques, such as polishing of Si 3 N 4 balls for bearing applications. 6 In CMP, however, the manufacturing technique has outdistanced its underlying science. Current CMP practices focus more on empirical developments of polishing "recipes" for each specific application. This makes the CMP process design a trialand-error procedure. Moreover, valuable insights gained in one application cannot be readily used under a modified set of circumstances. Such lack of scalability and migratability of experimental data hinders the CMP process design efforts. The lack of physical understanding also makes the process difficult to control and results in suboptimal process performance. Accordingly, the present work aims at developing a mechanistic model of material removal during a CMP process by addressing the role of the employed porous pad.There exist several material-removal models for the CMP process. The oldest and most commonly used is Preston's model: 7 Ḣ ϭ C и P o и u, where Ḣ is the average thickness removal rate, P o is the applied pressure, u is the relative velocity between the pad and the wafer, and C is Preston's coefficient. Preston's equation is based on the observation in glass polishing and is an empirical model; however, it gives a good estimate of the material-removal rate (MRR) in CMP.Expressing the removal rate as a linear function of both normal and shear stresses, Wang et al. 8 and Tseng et al. 9 proposed a modification to the assumption of linearity inherent in Preston's equation. Using the analogy of the removal process to a traveling indenter problem and the principles of elasticity and fluid mechanics, they derived a feature-scale model with and u 1/2 dependence on the removal rate. Recently, Zhao and Shi 10 proposed a model of CMP based on elastic contact and soft-pad response. They proposed a dependence of for MRR and in-P 2/3 o P 5/6 o The role of a porous pad in controlling material-removal rate (MRR) during the chemical-mechanical planarization (CMP) process has been studied numerically. The numerical results are used to develop a phenomenological model that correlates the forces on each individual abrasive particle to the applied nominal pressure. The model provides a physical explanation for the experimentally observed domains of pressure-dependent MRR, where the pad deformation controls the load sharing between active-abrasive particles and direct pad-wafer contact. The pr...

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