A Model of Chemical Mechanical Polishing

Abstract

A model of chemical mechanical polishing is presented which quantitatively correlates the polishing rate with the slurry concentrations of both chemicals and abrasives. The model predicts that as the concentration of either chemicals or abrasives is increased, an initial steep rise in the polishing rate is followed by an asymptotic approach to a maximum rate. The causes and implications of this behavior are discussed.Chemical mechanical polishing ͑CMP͒ has been described qualitatively as an alternation of chemical reaction and mechanical abrasion processes. 1 Although the removal rate for different systems has been characterized 2 experimentally in terms of the applied pad pressure and velocity, changes in concentrations of slurry chemicals and abrasive, and the composition of the pads and abrasives, 3-6 fundamental modeling of the system has been lacking. This paper provides a generic, semiquantitative description for both chemical and mechanical processes, and links these descriptions to form an overall model which predicts the removal rate as a function of the concentrations of chemicals and abrasives in the slurry.In conventional polishing, abrasive particles span a gap between the workpiece and the polishing pad. These particles support the externally applied load, which pushes the abrasive into the moving workpiece forming furrows and removing material. In conventional polishing, the removal rate is independent of both abrasive size and concentration, while the root mean square ͑rms͒ surface roughness increases with increasing abrasive size. 7 By contrast, in CMP, the polishing rate depends on abrasive concentration while the rms surface roughness is independent of abrasive size. 7 Understanding these differences involves a focus on the surface material that is removed.In conventional polishing, the removed material is identical to the bulk workpiece. In CMP, reactions between the workpiece and slurry chemicals produce a surface film. Material is removed by the abrasive separation of this film from the workpiece surface. Modeling this process involves describing the nature of the surface material formed, the chemical/workpiece reactions, and the abrasive/film interactions. Chemical Reaction ProcessIn the chemical process, the workpiece material reacts with chemical components of the slurry to form a thin reaction film. For a given workpiece surface, reactions with different chemicals can form different films, or can form similar films at different rates. Once formed, the surface films may decompose, or, they may dissolve or dissociate into the slurry at different rates. These chemical processes are independent of polishing and can be investigated under lab conditions without polishing abrasive present. Their reaction rates should provide insight into choosing practical CMP slurry components.The surface film formed in CMP is the result of a reaction between the workpiece material M and some chemical component C of the solution. This reversible surface reaction is subject to the laws of chemical equilibrium, ...

Modeling the effects of cohesive energy for single particle on the material removal in chemical mechanical polishing at atomic scale

“…(13), which generates opposite effects to this of value b on the removal rate. The relation MRR with b at high value of j shows similar trend with the results of the experimental data [27,28].…”

A Material Removal Rate Model for Aluminum Gate Chemical Mechanical Planarization

“…The equilibrium coverage of the surface complex is largely dependent on the concentration of chemicals and the relative rates of the formation and decomposition reactions. 21,22 The combination of chemical formation of the aluminum gate surface layer and its destruction by both chemical and mechanical processes leads to a steady state balance. In building the present model, the aluminum surface is modeled with the unreacted fresh surface [Al] and the reacted surface [Al(III)].…”

Material Removal Mechanisms in Lapping and Polishing

“…At low abrasive concentrations, this surface density increases with abrasive concentration because there is space on the lap for additional abrasives to stick. At high abrasive concentrations the lap becomes saturated and the surface density is constant because there is no more space for additional abrasives [69,70].…”