The Evolution Of Intergranular Microcracks In Copper Interconnects

With the rapid development of microelectronics technology, the major failure mode of Copper interconnect has drawn even more attentions. Based on the classical theory of surface diffusion and evaporation-condensation and its weak statement, a finite-element method is developed for simulating the shape instability of intergranular microcracks in copper interconnect due to surface diffusion induced by stress migration or electromigration. The main contents and conclusions of this paper are as follows.Based on the framework of the basic theory on dynamics about microstructure evolution, we derive the governing equations of the finite-element method about surface diffusion induced by stressmigration or electromigration. Then we develop the finite-element programs which are based on the model of an intergranular microcrack in Copper interconnect under the stress or the electric field, respectively, for simulating the microcrack evolution. The reliability and accuracy of the program is verified in details.Through the simulation under surface diffusion induced by stress migration, the paper arrives at the conclusions: there exist critical values of the stress and the aspect ratio for intergranular microcrack splitting. The splitting time of the intergranular microcrack decreases with increasing the stress or the aspect ratio. The splitting time and the critical values of the stress increase as the linewidth increases. The splitting time of the intergranular microcracks is less than that of the intragranular microcracks. The higher of the ratio between the grain-boundary energy and the surface energy, the shorter of the splitting time will be.After the simulation under surface diffusion induced by electromigration, this paper gets the results that there also exist critical values of the electric field and the aspect ratio for microcrack splitting. The increase of the electric field or the aspect ratio is beneficial to intergranular splitting and might accelerate microcrack splitting. The splitting time and the critical values of the electric field increase as the linewidth increases. The thermal field can increase critical values of the electric field. The splitting time of the intergranular microcracks is less than that of the intragranular microcracks. The existence of the grain boundary accelerates microcracks splitting.