Wire sizing and spacing for lithographic printability optimization
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As the VLSI feature size has already decreased below lithographic wavelength, the printability problem due to strong diffraction effects poses a serious threat to the progress of VLSI technology. A circuit layout with poor printability implies that it is difficult to make the printed features on wafers follow designed shapes without distortions. The development of Resolution Enhancement Techniques (RET) can alleviate the printability problem but cannot reverse the trend of deterioration. Moreover, over-usage of RET may dramatically increase photo-mask cost and increase the cycle time for volume production. Thus, there is a strong demand to consider the sub-wavelength printability problem in circuit layout designs. However, layout printability optimization should not degrade circuit timing performance. In this paper, we introduce a wire sizing and spacing method to improve wire printability with minimal adverse impact on interconnect timing performance. A new printability model is proposed to handle partially coherent illuminations. The difficult problem of printability optimization due to its multimodal nature is handled with a sensitivity based heuristic in timing aware fashion. Lithographic simulation results show that our approach can improve the printability in term of EPE (Edge Placement Error) by 20% - 40% without violating timing, wire width and spacing constraints.
author list (cited authors)
Cao, K. e., Hu, J., & Cheng, M.