Atomic layer deposited self-forming Ru-Mn diffusion barrier for seedless Cu interconnects

Abstract

Ru-based alloy thin films were prepared by atomic layer deposition (ALD) at a deposition temperature of 225 degrees C for use as a diffusion barrier for seedless Cu interconnects. Ru-Mn alloy thin films were grown by a repetition of super-cycles consisting of multiple Ru and Mn ALD sub-cycles. Ru and Mn ALD was performed using a sequential supply of a Ru precursor [1-Isopropyl-4-methylbenzene (cyclohexa-1,3-diene) Ru (0)] and NH3 plasma, and a Mn precursor [bis(1,4-di-isopropyl-1,3-diazabutadienyl) Mn(II)] and H-2 plasma, respectively. Secondary ion mass spectrometry (SIMS) indicated that Mn had been incorporated successfully into the Ru film by the periodic addition of Mn ALD sub-cycles during the ALD-Ru process. Plan-view transmission electron microscopy (TEM) showed that the grain size was reduced obviously from similar to 15 nm (pristine Ru) to similar to 8 nm (Ru-Mn alloy) and continuous columnar grain growth of the ALD-Ru film was prevented by the addition of the periodic Mn ALD sub-cycles. After annealing at 500 degrees C, the formation of a MnSiOx diffusion barrier was observed between the Ru-Mn film and underlying SiO2 surface by both cross-sectional view TEM and energy dispersive spectroscopy analysis and confirmed by SIMS depth profile. X-ray diffraction showed that the ultrathin ALD Ru-Mn thin film (similar to 5 nm) prevented Cu diffusion up to an annealing temperature of 600 degrees C, whereas the ALD-Ru thin film with the same thickness failed to prevent Cu diffusion only after annealing at 500 degrees C. Finally, the capability of the direct plating of Cu was demonstrated on the annealed ALD Ru-Mn film. (C) 2016 Elsevier B.V. All rights reserved.