Mechanical stress evolution in metal interconnects for various line aspect ratios and passivation dielectrics
Both X-ray diffraction and finite element analyses were used to investigate the effects of various passivation dielectrics and metal line aspect ratios on the mechanical stress in AlCu interconnect lines. Volume-averaged stresses were measured and calculated by considering not only residual stresses and mechanical properties of passivation dielectrics but also their characteristic deposition shapes. Interconnect stress increased with increasing passivation stiffness and line aspect ratio due to the normal constraint by passivation dielectrics, while it was relaxed in narrow lines passivated with voided or air-gapped dielectrics. A reasonable correlation between the measured and calculated stresses was found when void or gap in dielectric between metal lines was taken into account in numerical analysis.
metal interconnect aspect ratio passivation dielectrics thermal stress keyholes