Study on Grain Structures and Residual Stresses of Al and Cu Interconnects

Grain structures and stress states were observed and measured by using the x-ray diffractometer and the atomic force microscope for Cu and Al interconnect lines fabricated by damascene processing and reactive ion etching processing, respectively.Due to the influence of the mechanical stress on the Cu line in the damascene trench, the grain size of Cu lines (45~65nm) was smaller than that of Al lines (200~300nm) ;the strength of (111) texture of Cu lines (2.56) become weaker than that of Al lines (15.35) ;and the stress across the lines σ₂₂ increased with the decrease in Cu line width, i.e., for deposited and annealed Cu lines, σ₂₂ increased from ~ 73 and ~ 250MPa (4μm-line width) to ~ 104 and 301MPa (0.5μm-line width) , respectively.The hydrostatic stress σ was tensile for Cu and Al lines.Stresses, σ₁₁、σ₂₂ and σ₃₃ of Al lines increased with decrease in Al film thickness.Stresses, σ₁₁、σ₂₂ and σ₃₃ of Al lines decreased after annealing, indicated that thermal stress was the main contributor to residual stress in Al lines.