Atomic layer deposited Mo2N thin films using Mo(CO)(6) and NH3 plasma as a Cu diffusion barrier

Abstract

Thin films of molybdenum nitride (Mo2N) are prepared using sequential exposure of molybdenum hexacarbonyl [Mo(CO)(6)] and NH3 plasma in a plasma-enhanced atomic layer deposition (PEALD) reactor. Several process parameters such as the deposition temperature, plasma power, and post-annealing conditions are systematically investigated to achieve the best quality films. The superior growth kinetics is evident with a significantly higher growth per cycle (GPC) value with lower incubation period for this PEALD process (similar to 1.1 angstrom, similar to 36 cycles) when compared to thermal ALD (similar to 0.3 angstrom, similar to 63 cycles), both carried out at 200 degrees C. The growth rate of the Mo2N film reveals a significant jump above 215 degrees C, indicating a severe decomposition of Mo(CO)(6), however, polycrystalline gamma-Mo2N films with face-centered-cubic structure are evident within the deposition temperature range of 200-230 degrees C. The sharp decrease in the resistivity of the as-grown Mo2N films is observed with increasing deposition temperature, film thickness, and plasma power. The resistivity could be further lowered by a post-annealing process and the lowest resistivity of similar to 395 mu Omega cm is achieved for the thin film deposited with 300 watt plasma power and annealed at 700 degrees C. Finally, the Cu-diffusion barrier capability of an extremely thin film (similar to 7 nm) of as-deposited Mo2N is evaluated in Cu/PEALD-Mo2N/Si structure. The X-ray diffractometry analysis confirms that such a thin layer can successfully prevent the diffusion of Cu up to 500 degrees C and significant Cu3Si formation was observed only at 600 degrees C and above. The gradual failure of the diffusion barrier upon annealing is further investigated using electrical impedance (EI) analyses in two different modes. In-plane EI measurements directly indicate the change in the Cu layer at the top, and the formation of Cu3Si can be inferred from the through-plane mode. A comparison with PEALD and thermal-ALD-grown MoNx from EI analyses further reflects the superiority of plasma-enhanced process towards fabricating diffusion barrier layer. (C) 2020 Elsevier B.V. All rights reserved.