Study of electromigration in integrated circuits at design level

Abstract

Electromigration damage in interconnects is a well-known bottleneck of integrated circuits, because it causes reliability problems. Operation at high temperatures and current densities accelerates the damage, increasing the interconnect resistance and, therefore, reducing the circuit lifetime. This issue has been accentuated with the technology downscaling. To guarantee the interconnect reliability and, as a consequence, the integrated circuit reliability, traditional methods based on the so-called Blech Effect and on the maximum allowed current density are implemented during interconnect design. These methods, however, do not take into account the impact of the electromigration on the circuit performance.In this work the traditional approach is extended and a method to evaluate the effect of the electromigration in an integrated circuit performance is developed. The method is implemented in a tool which identiĄes the critical interconnect lines of an integrated circuit and suggests the proper interconnect width based on different criteria to mitigate the electromigration damage and to increase the reliability. In addition, the variation of performance parameters of the circuit as an interconnect resistance changes is determined.The tool is incorporated into the design Ćow of the integrated circuit and uses the data from design kits and reports directly available from the design environment.An accurate analysis of the temperature distribution on the interconnect structure is essential to a better assessment of the interconnect reliability. Therefore, a model to compute the temperature on each metallization level of the interconnect structure is implemented.The temperature distribution on the metallization layers of different technologies is investigated. It is shown that the temperature in the Metal 1 of the Intel 10 nm can increase by 75 K, 12 K higher than in the Metal 2. As expected, the layers that are closer to the transistors undergo a more signiĄcant temperature increase.The tool is applied to evaluate the interconnects and the robustness of different circuits, namely a ring oscillator, a bandgap voltage reference circuit, and an operational ampliĄer, against electromigration. The operational ampliĄer, in particular, is thoroughly studied.The proposed methodology identiĄes critical interconnects which under electromigration cause large variations in the performance of the circuit. In a worst-case scenario, the cutoff frequency of the circuit varies by 65% in 5 years of operation. An interesting Ąnding is that the proposed methodology identiĄes critical interconnects which would not be identiĄed by the traditional criteria. These interconnects have current densities below the limit recommended by the design rules. Nevertheless, one of such an interconnect leads to a variation of 30% in the gain of the operational ampliĄer. In summary, the proposed tool veriĄed that from the 20% paths with a critical current density, only 3% degrades signiĄcantly the circuit performance.This work brings the study of the reli...