Silicide formation in metal/Si structures and diffusion barrier properties of CVD tungsten films

Tungsten films were deposited on Si substrates by the H 2 or Si reduction of WF 6 under various experimental conditions. The composition and structure of as-deposited samples as well as the interfacial reactions and interdiffusion of elements in annealed samples were characterized by nuclear reaction analyses, sheet resistance measurements, x-ray diffraction technique, and Rutherford backscattering spectroscopy. The amount of oxygen at W–Si interfaces was found to be dependent on the cleaning treatment of the Si surface used before WF 6 –Si interaction. The interfacial oxygen concentration was less than 1 ⊠ 10 14 at./cm 2 (detection limit of the nuclear reaction analysis) and (2–7) ⊠ 10 16 at./cm 2 using an HF cleaning and the RCA treatment, respectively. For W/Si samples, the formation temperature of WSi 2 was dependent on the dopant level in the Si substrates and the oxygen concentration at W–Si interfaces. The silicidation reaction occurred at 625 °C in “oxygen free” W/Si structures while for structures containing interfacial oxygen atoms, this reaction occurred above 800 °C. In Al/W/Si structures, the intermetallic compound, WAl 12 , was formed by annealing at 450 °C for 90 min. Furthermore, the formation of WSi 2 was observed in structures annealed at a temperature in the range of 550 °C–600 °C regardless of the oxygen concentration at the W–Si interface. A model to explain the effect of interfacial oxygen atoms on the silicidation reaction and the influence of the Al overlayer on the thermal stability of Al/W/Si structures is proposed and discussed in this paper.