Karl M. Robinson

Modeling of Chemical Mechanical Polishing Processes Using a Discretized Geometry Approach

A transport-based, three-dimensional numerical modeling approach has been developed to simulate chemical mechanical polishing processes occurring in microelectronic materials processing. A unique aspect of this model is that the detailed morphology of the slurry flow domain between the wafer and polishing pad is approximated with a regularly updated sequence of geometries evenly positioned along the polishing orbit. Additionally, the modeling approach allows the use of any constitutive relationship for the rheological behavior of the polishing slurry. The local polishing rate is taken to be proportional to the local hydrodyanmic shear stress generated on the to-be-polished wafer surface. To illustrate the modeling approach, the development of planarity during polishing of a prototypical 3 X 3 array of square roughness elements was simulated. The rheology of the polishing medium was described as a power-law fluid with a Newtonian plateau, which is appropriate for an aqueous slurry of colloidal silica. Two modes of pad-to-wafer tracking during polishing are discussed. Modeling results show good agreement with typical experimental data.

The Influence of Feature‐Scale Surface Geometry on CMP Processes

The influence of feature-scale surface pattern dimensions on chemical mechanical polishing (CMP) processes has been studied through numerical simulations using a discretized geometry approach. The development of planarity for a symmetrical 3 X 3 array of square roughness elements with various lateral dimensions and spacing was simulated. Geometrical shielding of roughness elements by neighboring elements was found to cause asymmetrical surface polishing during the CMP processes. Given a specified trench spacing, a stronger doming effect was predicted for smaller sized protrusions. For a fixed feature size, the most significant doming effect was found to occur when the trench width is comparable to the gap size between the pad and the protrusion. These effects can be associated with variations in the flow pattern of the polishing slurry in the vicinity of the roughness elements.