On temperature planarization effect of copper dummy fills in deep nanometer technology

The continuous increase in interconnect joule heating and the advent of low-k ILD materials poses serious thermal challenges for multilevel interconnects in deep nanometer technologies. Vertical heat sinking paths are severely constrained by the limited via-density of the upper metal layers and poor thermal conductivity of the inter-layer dielectric. The lack of adequate vertical thermal conduction can lead to formation of `heat-traps` in the metal-layers affecting both performance and reliability of structures in the vicinity. We propose the usage of dummy metal-fills as horizontal thermal conduits to planarize hotspots generated in thermally isolated zones. The metal fills which are an integral part of the CMP planarization process can improve the effective thermal conductivity of the metal layers and can be used to carry out controlled heat re-direction. We have performed 3-D thermal simulations using an FEM solver and validated our scheme for different metal layers. With a pattern-density overhead of <=5%, the temperature differences across measurement points can be reduced by 50-70%. We have evaluated the efficacy of different metal shapes, sizes and orientation in terms of their heat-spreading capability.