Modeling of chemical mechanical polishing at multiple scales

Chemical Mechanical Polishing (CMP) has grown rapidly during the past decade as part of mainstream processing method in submicron integrated circuit manufacturing because of its global or near-global planarization ability. However, CMP process is influenced by many factors and is poorly understood. It makes process control and optimization very difficult. This study focuses on the modeling and simulation to facilitate better understanding and better control of the CMP process. The thesis outlines the modeling of CMP process in three scales: particle scale for material removal mechanism, wafer scale for within wafer nonuniformity issues and feature scale for dishing and erosion in metal CMP.; At the particle scale, material removal mechanism is assumed to be due to local plastic deformation of wafer surface at the abrasive - wafer interface. Pad is assumed to deform like a beam to obtain an approximate force partition between abrasives and direct wafer-pad contact. A mechanistic material removal model is derived that delineates the influence of abrasive (shape, size and concentration), pad (rigidity) and process parameters (pressure and relative velocity) on the material removal rate (MRR).; Wafer scale model is based on the solution of indentation of elastic half space by a rigid frictionless polynomial punch. The elastic solution is derived through potential theory and complex analysis method. It is valid for any polynomial punch with integer power or non-integer power. The load-displacement relationship is also derived and the conditions for unbonded or bonded contact are obtained from the boundary condition at punch edge. The corresponding viscoelastic solution is obtained through Laplace transform and elastic-viscoelastic analogy. The elastic solution is used to explain the edge effect. The elastic analytical solution is first verified against numerical results from Finite Element Method (FEM) simulation. It shows wafer curvature, indentation depth and load will influence the interface pressure distribution throughout the wafer surface and it introduces parameters control as a potential avenue for completely eliminating the within wafer nonumiformity. Viscoelastic solution is used to explain within wafer nonuniformity, i.e., edge effect and wafer to wafer nonuniformity, i.e., removal rate decay for unconditioned pad. The relationships among wafer-pad interface pressure, wafer shape and wafer loading condition are also investigated.; Feature scale model for dishing and erosion is based on Preston's relationship for material removal and constant downforce. It shows dishing will reach a limit and is governed by polishing conditions (overpolishing, pressure, velocity), slurry (selectivity), pad character istics (pad stiffness and bending ability), as well as wafer surface feature topography (pattern density, linewidth and pitch). This model is also valid for step height reduction when the same surface material is polished.; Due to process complexity and coupling of various parameters, more fundamental research needs to be carried out and carefully designed experiments need to be done to verify the models. Recommendations for future research work is presented at the end.