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

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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.