Atomic layer deposition of Co using N₂H₂ plasma as a reactant

Cobalt thin films were deposited by plasma-enhanced atomic layer deposition (PE-ALD) using CoCp₂ as a precursor and N₂H₂ plasma as a reactant. We systematically investigated the changes in Co film properties depending on N₂H₂ gas flow ratio to study the role of N during PE-ALD Co. With increasing N₂ flow ratio, the resistivity decreased reaching minimum value at f_N2H2 0.25 ∼ 0.33, which corresponds to the atomic ratio in NH₃ molecule, and then increased. With only N₂ or H₂ plasma, films with very high sheet resistance over 1 Msq were deposited. The chemical compositions of Co films were analyzed by x-ray photoelectron spectroscopy (XPS) and thickness and conformality were determined by x-ray reflectometry (XRR) and field emission scanning electron microscopy (FE-SEM), respectively. Then, the silicidation of PE-ALD Co films producing epitaxial CoSi₂ were investigated by x-ray diffraction (XRD) and high-resolution cross-sectional transmission electron microscopy (HR-XTEM).