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Abstract

A method for improving non-uniformity of chemical mechanical polishing by over coating layer is disclosed. The essential point of the invention is that an over coating layer is formed over a surface before the surface is planarized by a chemical mechanical polishing process. Note that polishing rate of the over coating layer must be less than the polishing rate of the surface, where the ratio of polishing rate is called as selectivity. Because the topography of the surface is not uniform, the topography of the over coating layer also is non-uniform and then the polishing probability in different parts of the over coating layer is different. Obviously, when the over coating layer on the higher area part of the surface is totally consumed, these are residual over coating layer on the lower area part of the surface. Thus, over polishing in the lower area part is prevented by residual over coating layer. Before total over coating layer is polished, the polished account of the surface is higher in the high area part and is lower in the lower area part. Thus, uniformity of the surface is enhanced. Moreover, enhancement of uniformity is direct proportional to product of selectivity and depth of over coating layer.

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First Claim