Tantalum nitride based thin films have been deposited on p-Si (100) and SiO 2 /Si by thermal Atomic Layer Deposition (ALD) using either the Ta(=N t Bu)(NEt 2 ) 3 or a derivative, in which one dialkylamido ligand is substituted by a η 5 -cyclopentadienyl (η 5 -Cp), as metal organic precursors with ammonia as reducing agent. TaN x C y self-limiting temperature dependent ALD growth was achieved for the TaCp(=N t Bu)(NEt 2 ) 2 /NH 3 process with a growth rate of 0.51–0.91Å cycle −1 in the 400–425°C temperature range while between 240 and 280°C, the growth of TaN based films from the Ta(=N t Bu)(NEt 2 ) 3 was accompanied by a partial decomposition of the precursor. The η 5 -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(=N t Bu)(NEt 2 ) 2 tends more likely to form tantalum carbide compared to Ta(=N t Bu)(NEt 2 ) 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 1nm.