Effect of thin Mo2C layer on thermal stability of Si/SiO2/Ti/Cu system

The effect of introducing a thin Mo2C (30 nm) layer between Ti and Cu on the thermal stability of Si/SiO2/Ti/Cu system was studied using four-point probe (FPP), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDAX) and X-ray diffraction (XRD) techniques. The measured value of the sheet resistance in the bi-layered diffusion barrier structure does not show any change up to an annealing temperature of 750°C. The sheet resistance when measured after annealing at 800°C marginally increases but less than twice its value at room temperature. The XRD analysis indicated no copper diffusion and the formation of Cu3Si phase up to 800°C. The bi-layered barrier structure annealed at elevated temperature shows copper-depleted and agglomerated regions. The sheet resistance measurement, study of surface morphology and the XRD analysis confirm that the insertion of thin Mo2C layer increases the thermal stability of the system from 400°C to 750°C. The increased thermal stability of the system is ascribed to longer diffusion path length in the bi-layered system probably because of grain boundaries mismatch at Ti-Mo2C interface.