Atomic layer deposition of TaSix thin films on SiO2 using TaF5 and Si2H6

The atomic layer deposition (ALD) of TaSix thin films was achieved on SiO2 at 500 K through the repetition of separate, alternating exposures to TaF5 and Si2H6. Films were deposited and in situ analyzed by X-ray photoelectron spectroscopy (XPS) to evaluate growth kinetics, interfacial chemistry with the substrate, and film composition. The first 25 exposure cycles resulted in an average film thickness of only 0.3 nm. Afterward, film thickness increased linearly at a rate of ∼0.1 nm/cycle, and films deposited using 50 ALD cycles were about 2.5 nm thick. The formation of a Ta oxyfluoride interfacial compound was observed and attributed to the reaction of TaF5 with SiO2, based upon previous surface chemistry studies. After 150 cycles, films were thick enough to suppress photoelectrons from the substrate and substrate film interface. Based on XPS data, the surface composition of these as-grown films, which were cooled in Si2H6, was in atomic percent: 26.6% Ta, 51.3% Si, 17.9% F, 1.6% O and 2.6% C. After 30 s of sputtering with 5 keV Ar ions, the F XPS signal was at the noise level indicating negligible fluorine incorporation in the films. The Ta 4f and Si 2p XP spectra are consistent with zero-valent Ta and Si, most likely as a non-stoichiometric tantalum silicide-like phase.