For a diffusion barrier against Cu, tantalum nitride (TaN) films have been successfully deposited by both conventional thermal atomic layer deposition (ALD) and plasma assisted atomic layer deposition (PAALD), using pentakis (ethylmethlyamino) tantalum (PEMAT) and ammonia (NH3) as precursors. The growth rate of PAALD TaN at substrate temperature 250° was slightly higher than that of ALD TaN (0.80 Å/cycle for PAALD and 0.75 Å/cycle for ALD). Density of TaN films deposited by PAALD was as high as 11.0 g/cm3, considerably higher compared to the value of 8.3 g/cm3 obtained by ALD. The N: Ta ratio for ALD TaN was 44: 37 in composition and the film contained approximately 8∼10 atomic % carbon and 11 atomic % oxygen impurities. On the other hand, the ratio for PAALD TaN layers was 47: 44 and the respective carbon and oxygen contents of TaN layers decreased to 3 atomic % and 4 atomic %. The stability of 10 nm-thick TaN films as a Cu diffusion barrier was tested through thermal annealing for 30 minutes in N2 ambient and characterized by XRD, which proves the PAALD deposited TaN film to maintain better barrier properties against Cu below 800°.