Material Removal Regions in Chemical Mechanical Polishing: Coupling Effects of Slurry Chemicals, Abrasive Size Distribution and Wafer-Pad Contact Area, Part 1

A material removal rate (MRR) model as a function of abrasive weight concentration has been proposed by extending a material removal model developed earlier [1-2]. With an increase of the weight concentration of abrasives/MRR, three regions of material removal exist: first, a chemically dominant and rapid increasing region, whose range is determined by the generation/passivation rate and hardness of the surface passivation layer, second, a mechanically dominant linear region, where the material removal is proportional to the weight concentration, and third, a mechanical dominant saturation region, where the material removal saturates because the total contact area is fully occupied by the abrasives. The passive layer of the wafer surface is proposed to be a bi-layer structure. In the first part of this paper, a detailed model is proposed to explain that the transition from the first to the second region is due to a transition from a wafer surface covered with a single soft material to a surface covered with both soft and hard materials. The chemicals contribute to the material removal through the generation rate of the upper softer layer of the passive films. The slope of the linear region is a function of abrasive size distribution, and the saturation removal rate is a function of abrasive size distribution and wafer-pad contact area. These are supported by experimental results to be discussed in the second part of this paper [39]. The model can help to clarify the roles of chemicals, wafer-pad contact area and abrasive size distribution in chemical mechanical polishing