Huang-Yu Chen
ABSTRACT
In the nanometer IC design, dummy fill is often performed to improve layout pattern uniformity and the post-CMP quality. However, filling dummies might greatly increase interconnect coupling capacitance and thus circuit delay, and might also lead to explosion of mask data due to the extra layout patterns. Traditional dummy-fill algorithms try to make each tile (window) density satisfy foundry's density upper and lower bounds under the coupling constraint. As technology advances, however, it is not sufficient to just keep the pattern density variation of each layer within density bounds. The density gradient, besides the density variation, plays a pivotal role in determining the post-CMP thickness of modern circuit designs. In this paper, we present the first gradient-driven dummy-fill algorithm to address the density gradient and other classical objectives (such as density variation, coupling constraints, dummy count) as well. Our dummy-fill algorithm has the two distinguished features: (1) Gaussian smoothing based gradient-driven multilevel dummy density analysis to minimize density gradient level by level, and (2) ILP-based fill synthesis to insert the fewest dummies within the coupling-violation-free feasible regions while satisfying the density constraints. Experimental results show that our algorithm can achieve promising results by inserting minimal dummies to reduce the density gradient and variation under the coupling constraints with a reasonable runtime overhead.
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Digital Library
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Index Terms
- Density gradient minimization with coupling-constrained dummy fill for CMP control
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