Jianfeng
Luo
Sponsored
By: NSF and UC SMART
Abstract
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.
Keywords:
abrasive weight concentration, abrasive size distribution, chemical-mechanical
polishing, hardness, material removal rate, pad, passivation, wafer.
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