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In order to characterize and model the pitch dependency of the step-height decay in a typical oxide CMP process, we measured surface profiles for line-space patterns at 50% density but different pitches. The profiles are analyzed in the spatial frequency domain. For long polishing times, we find a linear dependency between the exponential decay rate and the spatial frequency. From this observation, we derive a simple mathematical model to calculate the post-CMP topography based on the layout density. Application to a typical DRAM metalization layer shows remarkably good qualitative agreement with an error in the predicted heights of plusmn15 nm.