Studies of two-dimensional h-BN and MoS2 for potential diffusion barrier application in copper interconnect technology

Abstract

Copper interconnects in modern integrated circuits require a barrier layer to prevent Cu diffusion into surrounding dielectrics. However, conventional barrier materials like TaN are highly resistive compared to Cu and will occupy a large fraction of the cross-section of ultra-scaled Cu interconnects due to their thickness scaling limits at 2–3 nm, which will significantly increase the Cu line resistance. It is well understood that ultrathin, effective diffusion barriers are required to continue the interconnect scaling. In this study, a new class of two-dimensional (2D) materials, hexagonal boron nitride (h-BN) and molybdenum disulfide (MoS₂), is explored as alternative Cu diffusion barriers. Based on time-dependent dielectric breakdown measurements and scanning transmission electron microscopy imaging coupled with energy dispersive X-ray spectroscopy and electron energy loss spectroscopy characterizations, these 2D materials are shown to be promising barrier solutions for Cu interconnect technology. The predicted lifetime of devices with directly deposited 2D barriers can achieve three orders of magnitude improvement compared to control devices without barriers.

Interconnect technology: atomically thin h-BN and MoS₂ mitigate Cu diffusion

Atomically thin h-BN and MoS₂ may provide a viable alternative to conventional barrier materials in Cu interconnects. A team led by Zhihong Chen at Purdue University utilized two-dimensional crystals to mitigate Cu diffusion into the dielectric, a known cause of chip failure. By means of time-dependent dielectric breakdown measurements to investigate the diffusion barrier properties of atomically thin h-BN and MoS₂, they recorded a substantial improvement of the time-to-breakdown, owing to a reliability enhancement of the dielectric underneath Cu under normal operating conditions. A number of structural and electrical characterizations, including scanning transmission electron microscopy, energy dispersive X-ray spectroscopy, and electron energy loss spectroscopy confirmed that two-dimensional h-BN and MoS₂ films effectively prevent Cu diffusion, highlighting their potential applicability as sub-nanometer barrier for interconnect technology.