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

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 NbC x thin films deposited using a novel liquid metal–organic precursor [bis(cyclopentadienyl)( tert -butylimido)(methyl)niobium(V)] and H 2 plasma as the reactant. The films were grown by plasma-enhanced ALD (PEALD) on SiO 2 substrates at 100–400 °C, achieving a self-limiting growth rate of 0.19 Å/cycle at 350 °C. The as-grown NbC x film was crystalline with significant oxygen incorporation, which decreased (∼5 at. %) with higher deposition temperature and plasma power, leading to metal-rich NbC x 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 O 2 and H 2 O 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 NbC x (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/m 2 ) with NbC x films, particularly for the Ru (40 nm)/NbC x (2.6 nm)/SiO 2 (100 nm) structure compared to Ru (40 nm)/SiO 2 (100 nm), demonstrating ultrathin NbC x sufficient to prevent delamination during chemical–mechanical polishing in the back-end-of-line process as advanced adhesion-promoting layers.