Electromigration Reliability Of Ultra-fine Interconnection In Integrated Circuit

As the IC package is developing towards high-density, high speed and miniaturization, the ideal IC package is supposed to have the characteristics of high integration and high clock frequency and low energy consumption. The reliability of IC package is becoming increasingly significant. There are many problems to be solved urgently in application of traditional Al interconnection, among which the electromigration problem is particularly prominent.In this paper, a series of chips with Al interconnection were designed and fabricated. The morphology and physical properties of metallization interconnection were tested respectively. The resistance to electromigration and their thermal stress at high temperature were studied with experiments and FEA method. The relationship between structural feature of metal interconnection and the resistance to electromigration was put forward.The results showed that the shape, width and thickness of Al interconnection was precisely controlled. Profiler showed the surface roughness was small. Four-probe resistance analysis showed that the resistivity of Al film was 4.699×10-/Ω·m and it could fit the basic electrical properties requirements. The surface of electromigration cavities was very smooth without any deformation or necking phenomenon.Simulation on current distribution showed that chips with Al interconnection need a higher voltage, however, stress simulation showed that the structures of standard blech Cu interconnects would produce a greater thermal stress compared to Al interconnect. It was confirmed that the spots located in the joint of interconnections with different cross sectional areas and located inside the interconnection with a crack on surface endured both greater current density and thermal stress. The first main stress reached the maximum value inside the via, and reached the minimum value above and underneath the via inside the interconnection. The simulation results indicated that the first main stress increased as the via angle increasing and the first main stress reached its peak value when the via diameter was 350nm.Under the condition of constant current the longer electrical connections last, the more significant the migration-voids and interconnection deformation were, and even a interconnection collapse phenomenon was found. The growth rate of voids increased when the current density grows. Compared with AC modes, it was easier for voids to nucleate under a DC mode. The resistance of metal interconnection increased while electrical connections lasted, and its growth rate increased when a higher current density was loaded. Observation into structures with 50% more resistance growth showed that the electromigration had began. The interconnections reached its electromigration failure point faster at higher temperatures. According to the experiments and simulation results, a formula of failure time prediction was given.