Characterization of VLSI interconnect materials: Mechanical behavior, time-dependent plasticity, and electromigration

Abstract

Various thin film metallizations were tested in order to gain insight into their performance as VLSI interconnects. Biaxial stress-strain test results exhibited limited ductility, even for pure FCC metals such as copper and aluminum. This may be caused by the columnar structure which does not present the same resistance to crack propagation as a random polycrystalline structure. A Hall-Petch relationship determined for bulge testing of pure aluminum is comparable to another worker's results for films tested by the substrate curvature method. Al-Cu(2%) alloys are shown to have a response to precipitation hardening similar to that of bulk material of the same composition. Uniaxial tension testing of thin films is problematic because of wrinkles and edge defects associated with sample preparation. Electromigration damage in Al-Si(1%) is accelerated by the presence of a tensile stress. Activation energies for creep of aluminum and Al-Cu(2%) are nearly identical to those determined in long term electromigration testing of 5 $\mu$m interconnect stripes.