Some Practical Issues of Curvature and Thermal Stress in Realistic Multilevel Metal Interconnect Structures

This paper presents the results of a systematic study of curvature and stress evolution during thermal loading in single- and multilevel interconnect line structures which have been deposited on a much thicker substrate. Effects of line aspect ratio, passivation geometry, and metal density within a metal-ization level on thermal stress evolution in the lines are addressed. The cur-rent analytical stress model enables us to predict that interaction between lines on the same level, i.e., in the lateral direction, is so strong that it cannot be neglected. A two-dimensional (2-D) finite element method has been used to verify the accuracy of the current model, while available experimental data have been compared with theory. In order to capture the exact variation of the thermal stresses at different metalization levels, and to investigate the effect of the upper level line arrangements on the stress states at the lower level, a three-dimensional (3-D) finite element analysis was employed. It can be seen that the interaction between levels in the vertical direction is quite weak when the thickness of the interlevel dielectric (ILD) layer becomes comparable to that of the metal layer. Key words: Copper, curvature, multilevel metalization, thermal stress, thin-film structur