Highly Conductive Ultrathin Niobium Carbide Thin Films as Next-Generation Diffusion Barriers for Cu and Ru Interconnects Prepared by Plasma-Enhanced Atomic Layer Deposition

Abstract

Precise control over thin film thickness and noncorrosive byproducts is crucial for semiconductor-device barrier layers. While atomic layer deposition (ALD) is widely used for conformal films, its application to niobium carbide (NbC) remains underdeveloped. This study presents highly conductive NbCx thin films deposited using a novel liquid metal-organic precursor [bis(cyclopentadienyl)(tert-butylimido)(methyl)niobium(V)] and H2 plasma as the reactant. The films were grown by plasma-enhanced ALD (PEALD) on SiO2 substrates at 100-400 °C, achieving a self-limiting growth rate of 0.19 Å/cycle at 350 °C. The as-grown NbCx film was crystalline with significant oxygen incorporation, which decreased (∼5 at. %) with higher deposition temperature and plasma power, leading to metal-rich NbCx with resistivity below 100 μΩ·cm about 100% coverage on 3D trench structure with an aspect ratio of ∼1.5. Density functional theory (DFT) calculations show that oxygen in deposited films results from the reaction of adsorbed precursors with O2 and H2O residues in the chamber. Besides, DFT results demonstrate that high plasma power and temperature conditions are required to sufficiently reduce strong Nb-O bonds and generate carbon sources, thereby leading to C-rich films. The diffusion barrier properties of the ultrathin NbCx (2.6 nm) film were investigated against Cu and Ru, withstanding diffusion barrier performance for Ru interconnects up to 900 °C. There is a 10-fold enhancement in the interfacial adhesion energy (17.77 ± 5.95 J/m2) with NbCx films, particularly for the Ru (40 nm)/NbCx (2.6 nm)/SiO2 (100 nm) structure compared to Ru (40 nm)/SiO2 (100 nm), demonstrating ultrathin NbCx sufficient to prevent delamination during chemical-mechanical polishing in the back-end-of-line process as advanced adhesion-promoting layers. © 2025 American Chemical Society.