Jianfeng Luo
Sponsored by NSF and UC SMART
Abstract- In this report, the with-in wafer non-uniformity (WIWNU) of
material removal rate and its optimization are discussed from both the
machine side and consumable side. At the machine side, the pressure
and velocity distribution are the major reasons for the non-uniform
material removal rate across the wafer. The velocity distributions for
the rotational type and linear type of machines are analyzed systematically.
The rotational part of the velocity is the contributor of the velocity
non-uniformity. The pressure non-uniformity in both cases of the solid-solid
contact and the solid-fluid-solid contact are discussed. Adding the
retaining ring is an effective way to reduce the pressure non-uniformity
at the edge of the wafer in the solid-solid contact mode. In the solid-fluid-solid
contact mode, the friction coefficient is identified as the major contributor
to the non-uniformity. A process window of pressure and velocity in
terms of small non-uniformity can be obtained by combining the model
proposed in this report and the Stribeck curve of the friction coefficients.
At the consumable side, a systematic method is proposed to optimize
the WIWNU in solid-solid contact mode, based on the material removal
model developed in previous works [5, 6, 7]. The basic idea is to reduce
the sensitivity of the material removal on pressure and velocity distribution.
Keywords: WIWNU, Velocity Distribution, Pressure Distribution, Solid-Solid
Contact, Solid-Fluid-Solid Contact, Friction Coefficients, Consumable
Effects, Modeling, Optimization.
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