Investigation of cosputtered W–C thin films as diffusion barriers

Polycrystalline thin films of W–C were deposited on single-crystal <111>Si or SiO2 substrates by rf planar magnetron cosputtering of graphite (C) and W targets. The performance of cosputtered W75C25 thin films as diffusion barriers between a <111>Si substrate and metallic overlayers of Ag, Au, or Al was investigated. Backscattering spectrometry and x-ray diffraction are used to detect metallurgical interactions. Four-point probe measurement of resistance is employed to monitor the electrical stability of the metallization schemes upon thermal annealing in a vacuum for 30 min in temperature ranges from 500 to 700 °C. The electrical resistivity of W75C25 films is 140 µOmega cm. A W75C25 layer 1100 Å thick prevents metallurgical interdiffusion and reaction between Au or Ag overlayers and the <111>Si substrates up to 700 °C, and between an Al overlayer and the <111>Si substrate up to 450 °C.