Electron-enhanced atomic layer deposition of Ru thin films using Ru(DMBD)(CO)₃ and effect of forming gas anneal

Ruthenium (Ru) thin films were deposited utilizing electron-enhanced atomic layer deposition (EE-ALD). Sequential exposures of Ru(DMBD)(CO)₃ (DMBD = 2,3-dimethylbutadiene) and low-energy electrons at ∼125 eV were used to grow the Ru films at temperatures ≤160 °C. The electrons were obtained from a hollow cathode plasma electron source that provided an electron current of ∼200 mA over a surface area of ∼4 cm². Low-energy electrons can desorb surface ligands derived from Ru(DMBD)(CO)₃, such as CO, through electron-stimulated desorption. The desorbed surface ligands leave chemically reactive sites for subsequent Ru(DMBD)(CO)₃ precursor absorption. Ru EE-ALD film growth was monitored utilizing in situ spectroscopic ellipsometry (SE). The electron exposures resulted in rapid Ru film nucleation and growth. Under saturation conditions at 160 °C, the growth rate for Ru EE-ALD was 0.2 Å/cycle. The electron efficiency factor for Ru EE-ALD was ∼21 500 electrons/deposited Ru atom. There was no film growth without electron exposures. Ru growth was observed on various substrates including silicon with native oxide and titanium. Ru growth was also obtained on insulating substrates such as 400 nm thick thermal SiO₂ substrates. XPS analysis measured <1 at. % oxygen in the deposited Ru films. XRD, x-ray reflectivity, and SE were used to characterize the Ru films before and after forming gas anneal (FGA). FGA successfully removed carbon impurities from the as-deposited Ru films. The resistivity of the Ru EE-ALD films after FGA was determined to be as low as 17 μΩ cm for a film thickness of 6.7 nm. SE measurements of the imaginary part of the pseudodielectric function, 〈ɛ₂〉, were utilized to characterize the as-deposited Ru films and the high purity Ru films after FGA. The low resistivity of the Ru films after FGA was consistent with a prominent Drude absorption in the $⟨ ε 2⟩$ spectrum at ≤1 eV. Various reactive background gases such as H₂, NH₃, and H₂O were utilized during EE-ALD to attempt to remove the carbon from the as-deposited Ru EE-ALD films.