Analysis of thermal stresses in metal interconnects with multilevel structures

The evolution of thermal stresses in aluminum interconnects was analyzed numerically. Particular attention was devoted to the effects of multilevel arrangement, which have been largely ignored in past studies. Two-dimensional models based on long metal lines with different aspect ratios and cross-sectional arrangements were employed. The metallization, taken to include thin refractory layers sandwiching the aluminum conductor, was embedded within silicon oxide dielectric on top of the silicon substrate. A thermal cooling process was simulated by recourse to the finite element method. It was found that the incorporation of refractory layers increases the stress in aluminum lines. The line aspect ratio, rather than the multilevel nature, plays the most important role in affecting the thermal stress. Issues related to interconnect stress modeling and reliability implications are discussed.