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 A cycle-1 in the 400-425 oC temperature range while between 240 and 280 oC, 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 oC, 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.