Characteristics of ALD tungsten nitride using B₂H₆, WF₆, and NH₃ and application to contact barrier layer for DRAM

Tungsten nitride (W Nx) thin films were grown by atomic layer deposition (ALD) within the temperature range of 200-350°C from diborane (B2 H6), tungsten hexafluoride (W F6), and ammonia (N H3) for application to a contact barrier layer in dynamic random access memory (DRAM). Herein, B2 H6 was used as an additional reducing agent to produce a low-resistivity ALD-W Nx film, and its resistivity was in the range of 300-410 μ cm, depending on the deposition conditions for the ∼10 nm thick film. An increase in the growth rate was observed with increasing deposition temperature, but an almost constant growth rate of ∼0.28 nmcycle was obtained in the temperature range from 275 to 300°C. The properties of the as-deposited film, including the resistivity, WN ratio, density, B and F impurity content, and phase, were affected by the deposition temperature and B2 H6 flow rate during the process. As the deposition temperature and B2 H6 flow rate increased, the WN ratio and film density increased and the impurity content decreased, leading to a reduction in the resistivity of the film. An increased WN ratio was found to be favorable to the formation of a face-centered-cubic Β- W2 N phase. Excellent step coverage was obtained even on a 0.14 μm diameter contact hole with an aspect ratio of 16:1. The ALD-W Nx film in this study was thermally stable to annealing at 800°C for 30 min, but after annealing at 900°C, it converted to body-centered-cubic α-W with the accompanying release of N. The ALD-W Nx film was evaluated as a barrier layer for W-plug deposition for 70 nm design-rule DRAM. The results showed that the integration scheme with ALD-W Nx showed lower contact resistance than metallorganic chemical vapor deposition TiN or Ti Cl4 -based chemical vapor deposited TiN.