Characteristics of ALD Tungsten Nitride Using B2H6, WF6, and NH3 and Application to Contact Barrier Layer for DRAM

Abstract

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