Highly-conformal nanocrystalline molybdenum nitride thin films by atomic layer deposition as a diffusion barrier against Cu

Abstract

Molybdenum nitride (Mo2N) thin films were grown by atomic layer deposition (ALD) using a sequential supply of a newly synthesized Mo metalorgranic precursor, Mo((NBu)-Bu-t)(2)((SBu)-Bu-t)(2), and H-2 plasma at a substrate temperature of 300 degrees C. A newly proposed ALD system exhibited typical ALD characteristics, such as a self-limited film growth and a linear dependency of the film thickness on the number of ALD cycles, and showed a growth rate of 0.028 nm/cycle on a thermally grown SiO2 substrate. Such the ideal ALD growth characteristics enabled excellent step coverage of similar to 80% for the ALD-grown Mo2N film onto nano-trenches with a width of 25 nm and an aspect ratio similar to 4.5. The optimized film had a resistivity as low as similar to 350 mu Omega-cm. X-ray diffraction, Rutherford backscattering spectrometry, and X-ray photoelectron spectroscopy analyses confirmed that formation of N-rich cubic Mo2N (N/Mo = similar to 0.7) phase with carbon and sulfur impurities of 2.6 and 7.4 at.%, respectively. Plan-view transmission electron microscopy analysis showed that the film formed a nanocrystalline microstructure with 5-8-nm-sized grains embedded in an amorphous matrix. An ultrathin (only similar to 4 nm-thick) ALD-grown Mo2N film effectively prevented diffusion of Cu into Si after annealing at a temperature even up to 650 degrees C. (C) 2015 Elsevier B.V. All rights reserved.