Atomic layer deposition of tantalum nitride based thin films from cyclopentadienyl type precursor

Tantalum nitride based thin films have been deposited on p-Si (100) and SiO2/Si by thermal Atomic Layer Deposition (ALD) using either the Ta(= NtBu)(NEt2)3 or a derivative, in which one dialkylamido ligand is substituted by a η5-cyclopentadienyl (η5-Cp), as metal organic precursors with ammonia as reducing agent. TaNxCy self-limiting temperature dependent ALD growth was achieved for the TaCp(= NtBu)(NEt2)2/NH3 process with a growth rate of 0.51–0.91 Å cycle−1 in the 400–425 °C temperature range while between 240 and 280 °C, the growth of TaN based films from the Ta(= NtBu)(NEt2)3 was accompanied by a partial decomposition of the precursor. The η5-cyclopentadienyl type compound allows lower nitrogen content in the precursor and thereafter in the deposited film. Although N/Ta ratio is close to one at temperatures of 390 and 400 °C, as analyzed by Rutherford Back Scattering and Nuclear Reaction Analysis, films were amorphous independently of the deposition temperature. Since Ta–C bonds are present in the Cp derivative, the TaCp(= NtBu)(NEt2)2 tends more likely to form tantalum carbide compared to Ta(= NtBu)(NEt2)3, which leads to lower thin film resistivity. For both precursors, employed in their respective ALD window, films were smooth with a root-mean-square roughness close to 1 nm.