Study of the low-pressure chemical-vapor-deposited tungsten-silicon interface: Interfacial fluorine

Abstract

Single-crystal silicon 〈100〉 substrates uniformly doped at ≳12 Ω cm with boron were deposited with ∼800 Å of low-pressure chemically vapor deposited W in a hot-quartz-walled (Anicon) system at a deposition temperature of 300 °C. The samples studied include an as-deposited sample and two others which were post-deposition annealed at 600 °C in Ar for 15 min each. X-ray photoelectron spectroscopy (XPS) coupled with an Ar+ ion sputter profiling technique was employed to investigate these structures as a function of depth. Particular emphasis was placed on the depth distribution, content, and chemical state of the fluorine present. Rutherford backscattering spectrometry and x-ray diffraction were used to corroborate the XPS data. Results show that, for the as-deposited and 600 °C annealed sample, the maximum concentration of fluorine (0.6–0.8 at. %) is observed, not at the W/Si interface, but rather at the W (H2 reduction)/W (Si displacement) interface. For the sample annealed at 850 °C, WSi2 is formed in the overlayer, and the peak in the F profile corresponds to the position of the WSi2/Si interface. The maximum concentration of fluorine is reduced by approximately 75% to 0.23 at. % in this sample. From the XPS spectra of the F 1s region, the chemical species of fluorine present in these samples have been identified as WF6, WF5, and WF4.