Appeal No. 2005-1220
Application No. 09/270,606 Page 8
Further testing has demonstrated that addition of a
modifier to ceria slurry, in particular ethylene
glycol, causes the polishing characteristics
illustrated in FIGS. 4, 5 and 6 to become more
conventional, as illustrated in FIGS. 2 and 3. This
characteristic is shown generally at 80 in FIG. 7,
which illustrates the effect of addition of 10% (FIG.
7a) and 20% (FIG. 7b) ethylene glycol, and a down
pressure of 6 psi.. A high area rate 82 is
approximately the same as blanket rate 20, while a low
area rate 84 remains close to zero. Characteristics
82a, 84a, represent a feature size scale of 2x2 :m;
characteristics 82b, 84b, represent a feature size
scale of 4x4 :m; characteristics 82c, 84c, represent a
feature size scale of 8x8 :m; and characteristics 82d,
84d, represent a feature size scale of 16x16 :m. A
convergence point 86 is depicted, but not really
achieved in the depicted results. Longer polishing
times result in the desired convergence and
planarization.
A 10%, by volume, addition of ethylene glycol results
in the polishing rate of high areas and the blanket
polishing rate to be nearly equal. In comparison, for
addition of 20% ethylene glycol by volume, the removal
rate has fallen below the blanket polish rate. This is
similar to conventional behavior. As expected, control
wafers polished in slurry with no ethylene glycol
modifier show the usual behavior. Ethylene glycol
concentrations up to 50% may be used.
The effect of the modifier can be offset by increasing
down force. The effect of a 50% increase in down force,
to 9 psi, for a 20% by volume addition of ethylene
glycol to ceria slurry is shown in FIG. 8, at 90. A
high area rate 92, low area rate 94 and convergence
point 96 are depicted, with the characteristics being
as described in connection with FIG. 7. The preferred
modifier is ethylene glycol, however, other modifiers
may work as well provided that they alter physical
properties of the slurry in the desired way. The
modifier may either be pre-mixed in the slurry
feedstock or introduced directly to the polishing table
to be mixed with slurry during processing. Ideally, the
modifier does not participate in the slurry chemistry,
but, only affects slurry physical characteristics,
i.e., viscosity, surface tension, etc. or
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