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| The Evolution of Intergranular Microcracks due to Surface Diffusion Induced by Electromigration |
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Abstract With the rapid development of microelectronics technology, more attention has been paid to the major failure mode of Copper interconnects. 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 caused by the electromigration-induced surface diffusion. A detailed discussion has been given about the impacts of the electric field , the aspect ratio , and the ratio of grain boundary energy to surface energy on the shape instability of intergranular microcracks. The results show that the evolution of the intergranular microcracks has two trends when they migrate along the electric field direction and the grain boundary: being a cylinder or splitting into two small intergranular microcracks (one is relatively larger than the other). There exist critical values of the aspect ratio and the electric field . When or , the intergranular microcrack will split into two smaller intergranular microcracks. The splitting time of the intergranular microcrack decreases with an increase in the electric field or the aspect ratio, indicating that the increase of electric field or aspect ratio accelerates microcrack splitting. The critical electric field decreases as the aspect ratio increases, and the critical aspect ratio decreases as the electric field increases. In other words, the increase of the electric field or the aspect ratio is beneficial to microcrack splitting. In addition, the splitting time of the intergranular microcracks is less than that of the intragranular microcracks. The existence of grain boundary accelerates microcrack splitting.
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Received: 14 April 2016
Published: 15 February 2017
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2017, Vol. 38 
