Electromigration Failure Analysis And Numerical Simulation Of Metal Micro-interconnects Under The Multi-physical Field

As the electronic products continue to push for miniaturization and high performance, the current densities in IC metal interconnects increase dramatically, which may cause electromigration (EM) failure. This thesis studies the electromigration failure of metal micro-interconnects, and presents a coupled multi-physics model for simulating such a failure. The present model considers four driving forces including the electron wind force, stress gradient, temperature gradient, as well as atomic concentration gradient induced forces. The coupled multi-physics modeling is combined with electromigration test to investigate the electromigration induced failure mechanisms of metal interconnects, which will provide us a theoretical and numerical analysis foundation for guiding the design and reliability evaluation of metal micro-interconnects.Firstly, according to the basic EM theory, the driving mechanisms of EM are summarized. The improved Atomic Flux Divergence (AFD) method is introduced and the existed problems of AFD method are discussed.Secondly, the atomic concentration redistribution equation is derived from EM evolution equation by a weighted residual method with considering a variety of EM driving mechanisms which includes the electron wind force, stress gradient, temperature gradient and atomic concentration gradient. The electric-thermal-structural coupled analysis based on ANSYS multi-physical simulation platform is performed to obtain the current density, temperature and stress distribution of the studied model. An EM atomic concentration redistribution algorithm is developed using FORTRAN code to get atomic concentration distribution of different time. The dynamic simulation of EM void evolution is performed to get TTF (Time to Failure) based on the criterion of void/hillock incubation and propagation. The simulated results based on SWEAT and CSP structures show good agreement with experimental observations, which verify the correction of the present developed algorithm. The impact of atomic concentration gradient on EM is studied and it shows that the atomic concentration will be retarded by considering the atomic concentration gradient item in the time-dependent EM evolution equation. Without consideration of the atomic concentration gradient, the TTF will be underestimated. The sensitivity analysis equations with considering EM parameters and mechanical properties of material as design variables are derived for EM sensitivity analysis. The results show that the EM is very sensitive to the activation energy of material and the mechanical properties of material have the minimal impact on EM.The standard wafer-level electromigration accelerated test and package level electromigration test are performed for metal line and via interconnect structures by using 0.18μm power technology respectively. The TTFs are obtained from the tests, at the same time, the microstructure evolution and damage mechanism are examined by scanning electron microscope (SEM) observation. The above mentioned algorithm is used to simulate the failure of these test structures and the results show that the predicted TTFs and EM failure location are well agreement with the test results. Both EM test and modeling results disclose the significant influence of chemical-mechanical planarization and barrier metal thickness on the EM failure life.