(RR) = -C1 {c U+ 21 1-1 3/2 PV (2.42)
v zC pA, El ) B B) R
As Eq. 2.23 indicates, the overall removal rate, (RR), is the thickness removal rate which
is the volumetric removal rate divided by the nominal wafer area Ao. We may recall that
C is a constant whose value is about 0.35 when h/o is between 0.5 and 3.0 [Joh85]. The
overall removal rate given above is reminiscent of Preston's equation in that the material
removal rate is proportional to the down-pressure, P, and the relative velocity, V. It
should be noted that the Preston's coefficient Kp, whose value relies on empiricism, is
now given as a function of various processing variables and material properties.
The model predicts the removal rate as a function of pressure and velocity product (PV)
very well [72]. The removal rate is usually only considered as a function of PV in many
modeling efforts, ignoring other processing parameters. But the PERC I model considers
the particle size effect, which is crucial for any CMP system.
Equation 2.41 indicates that the overall removal rate is independent of the particle size R
whereas Eq. 2.42 indicates a decrease in (RR) with increasing particle size. When the
indentation-depth is smaller than the surface layer thickness (i.e., 0)