Metal Inter-layer Via Keep-out-zone in M3D IC: A Critical Process-aware Design Consideration

Metal inter-layer via (MIV) in Monolithic three-dimensional integrated circuits (M3D-IC) is used to connect inter-layer devices and provide power and clock signals across multiple layers. The size of MIV is comparable to logic gates because of the significant reduction in substrate layers due to sequential integration. Despite MIV's small size, the impact of MIV on the performance of adjacent devices should be considered to implement IC designs in M3D-IC technology. In this work, we systematically study the changes in performance of transistors when they are placed near MIV to understand the effect of MIV on adjacent devices when MIV passes through the substrate. Simulation results suggest that the keep-out-zone (KOZ) for MIV should be considered to ensure the reliability of M3D-IC technology and this KOZ is highly dependent on the M3D-IC process. In this paper, we show that the transistor placed near MIV considering the M1 metal pitch as the separation will have up to $68,668\times$ increase in leakage current, when the channel doping is $10^{15} cm^{-3}$, source/drain doping of $10^{18}cm^{-3}$ and substrate layer height of $100\ nm$. We also show that, this increase in leakage current can also be reduced significantly by having KOZ around MIV, which is dependent on the process.