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

Abstract

Tungsten nitride (WNx) thin films were grown by atomic layer deposition (ALD) within the temperature range of 200-350 degrees C from diborane (B2H6), tungsten hexafluoride (WF6), and ammonia (NH3) for application to a contact barrier layer in dynamic random access memory (DRAM). Herein, B2H6 was used as an additional reducing agent to produce a low-resistivity ALD-WNx film, and its resistivity was in the range of 300-410 mu Omega cm, depending on the deposition conditions for the similar to 10 nm thick film. An increase in the growth rate was observed with increasing deposition temperature, but an almost constant growth rate of similar to 0.28 nm/cycle was obtained in the temperature range from 275 to 300 degrees C. The properties of the as-deposited film, including the resistivity, W/N ratio, density, B and F impurity content, and phase, were affected by the deposition temperature and B2H6 flow rate during the process. As the deposition temperature and B2H6 flow rate increased, the W/N ratio and film density increased and the impurity content decreased, leading to a reduction in the resistivity of the film. An increased W/N ratio was found to be favorable to the formation of a face-centered-cubic beta-W2N phase. Excellent step coverage was obtained even on a 0.14 mu m diameter contact hole with an aspect ratio of 16:1. The ALD-WNx film in this study was thermally stable to annealing at 800 degrees C for 30 min, but after annealing at 900 degrees C, it converted to body-centered-cubic alpha-W with the accompanying release of N. The ALD-WNx 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-WNx showed lower contact resistance than metallorganic chemical vapor deposition TiN or TiCl4-based chemical vapor deposited TiN. (c) 2007 The Electrochemical Society.