Laboratory for Manufacturing and Sustainability

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.