Achievement of Highly Flat Edge with Double-Layered Polishing Pad (Improvement of Edge Flatness with Softening Upper Layer)

概要

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As the substrates of semiconductor devices, silicon wafers are required to be highly flat in order to increase the integration density and the productivity of devices. Especially edge roll off, which is generated in polishing process as the final stage of the wafer manufacturing, is strongly demanded to be diminished. While various countermeasures are proposed and used practically, they cannot meet the demand. In the previous study, to meet the demand, a double-layered polishing pad having thin soft upper layer and hard lower layer was developed and the pad achieved the high surface flatness near the edge. On the basis of finite element structural analysis of a polishing model, the double-layered polishing pad with softer upper layer was expected to be more effective in diminishing edge roll off and, however, it is difficult to estimate the hardness of thin soft layer in actual. In this study, the indentation method based on the theory of elasticity was introduced to estimate the modulus of the above-mentioned upper layer. Modulus measurements on the polishing pads and polishing experiments on silicon wafers confirmed that the softer the thin upper layer is, the flatter the obtained wafer edge shape is and the newly developed double-layered polishing pad with softer upper layer improved surface flatness near the edge.