The Evolution Of Microcracks In Interconnects Induced By Stress Migration

With the rapid development of the microelectronics technology,the failure of interconnects in the integrated circuit raises wide attention.In this dissertation,based on the basic framework of the thermal kinetics theory of the mass transportation in materials,a finite element method is developed for simulating the evolution of intragranular and intergranular microcracks in interconnect induced by stress migration.The main contents and conclusions are as follows.Based on the classical theories and the weak statements of the interface migration and surface diffusion,the models of two-dimensional intragranular and intergranular microcracks are established.Then,we derive the governing equations of the finite-element method of the microstructural evolution caused by interface migration induced by stress migration and develop the corresponding finite-element program.The reliability of the program is also verified.The evolutions of intragranular and intergranular microcracks under the tensile stress due to the interface migration are simulated.And we systematically study the effects of the applied stress,the linewidth,the aspect ratio and the difference of chemical potential.The results show that: there exist two evolution trends of the shape instability for both of intragranular and intergranular microcracks,namely,propagation and shrinkage.And there exist critical values of the applied stress,the linewidth and the aspect ratio.The intragranular and intergranular microcracks will propagate more easily with the larger stress,the smaller linewidth or the bigger aspect ratio and the area of cavities will increase faster.Otherwise,the microcracks will shrink more easily and the area of cavities will reduce faster.Besides,the intergranular microcracks are more likely to expand along the grain boundary and the effect of grain boundary is more significant when the line width,the shape ratio or the stress are larger.Based on the classical theory of the interface migration and surface diffusion,a finite element method is developed for the simulation due to the two mechanisms induced by stress migration.The following conclusions are drawn: under two mechanisms,the intergranular microcrack will split into three small cracks when it propagate along the grain boundary.The ratio,that measures the competitive strength of two mechanisms,has great influence on the evolution of the microcracks.The microcracks will split faster with the larger ratio or the bigger aspect ratio.