Post-Deposition Plasma Treatment on Atomic-Layer-Deposited Tantalum Nitride Films for Enhancement of Copper Diffusion Barrier Performance

Abstract

Tantalum nitride (TaN) films are essential diffusion barriers in copper (Cu) interconnects, where they encapsulate Cu wires and prevent Cu diffusion into surrounding dielectric layers. Conventionally, TaN barriers are formed by either physical vapor deposition (PVD) or atomic layer deposition (ALD). As continued thickness scaling of Cu nano-interconnects demands ultrathin and conformal barriers, ALD is increasingly favored over PVD. However, ALD-TaN typically exhibits inferior barrier performance compared with PVD-TaN, posing a critical reliability challenge at reduced thicknesses. This performance gap primarily originates from the lower film density and higher impurity concentration inherent to ALD-TaN. Although hybrid ALD/PVD-TaN stacks partially balance conformability and barrier performance, they still limit further thickness downscaling.

In this study, I introduce plasma-based post-deposition treatment techniques to enhance the barrier performance of ALD-TaN without compromising its minimum conformal thickness. The treatment consists of sequential hydrogen and nitrogen plasma processes, both of which are fully compatible with conventional Cu metallization and are cost-effective. To quantitatively assess the impact of the plasma treatment, vertical capacitor structures–comprising a Samsung dielectric layer (100 nm), a Cu electrode (100 nm), and a 4-nm-thick ALD-TaN layer at the Cu/dielectric interfaces–were fabricated. Dielectric breakdown strength (VBR) was evaluated after annealing at 300 °C for 1 h. In untreated samples, annealing reduces VBR from ~50 V to ~20 V, indicating non-negligible Cu diffusion into the dielectric. Remarkably, however, plasma-treated ALD-TaN samples exhibit a higher VBR (~80 V), which remains nearly unchanged after annealing.

The enhanced barrier performance is attributed to a sequential microstructural transformation of ALD-TaN induced by the two-step plasma treatment. Hydrogen plasma initiates reduction reactions, including deoxidation, decarbonization, and even denitrification, yielding a purified yet porous Ta-rich TaN layer. Subsequent nitrogen plasma promotes nitridation and atomic rearrangement, resulting in a dense, low-defective TaN film comparable to that produced by PVD. This plasma-enabled postdeposition strategy may provide a viable pathway toward high-performance, ultrathin ALD-TaN barriers for Cu nano-interconnects.