CuTi as Potential Liner- and Barrier-Free Interconnect Conductor

CuTi layers are co-sputter deposited on 20-nm SiO2/Si(001) wafers at 350 °C to quantify their stability in direct contact with a dielectric and to explore the potential of CuTi as barrier- and liner-free interconnect metal. X-ray diffraction (XRD) pole figures indicate a preferred 001 out-of-plane crystalline orientation. Rutherford backscattering confirms a stoichiometric composition. Vacuum annealing tests at 450 °C of CuTi layers indicate considerably higher thermal stability than for pure Cu layers, including negligible dewetting observed by scanning electron microscopy (SEM) and negligible intermixing with the oxide substrate quantified by photoelectron spectroscopy. Four-point bend tests show a 25% higher interfacial toughness for CuTi/SiO2 than Cu/SiO2 interfaces. CuTi/SiO2 samples also exhibit a 300-times longer failure time than Cu/SiO2 during time-dependent dielectric breakdown (TDDB) tests using an externally applied 3-MV/cm electric field. The higher stability of CuTi in comparison to Cu is attributed to a higher cohesive energy in combination with an atomically thin self-limiting Ti oxide layer at the CuTi/SiO2 interface.