The role of Ru passivation and doping on the barrier and seed layer properties of Ru-modified TaN for copper interconnects

Abstract

Size reduction of the barrier and liner stack for copper interconnects is a major bottleneck in further down-scaling of transistor devices. The role of the barrier is to prevent diffusion of Cu atoms into the surrounding dielectric, while the liner (also referred to as a seed layer) ensures that a smooth Cu film can be electroplated. Therefore, a combined barrier+liner material that restricts the diffusion of Cu into the dielectric and allows for copper electro-deposition is needed. In this paper, we have explored barrier+liner materials composed of 1 and 2 monolayers (MLs) of Ru-passivated epsilon-TaN and Ru doped epsilon-TaN and focus on their interactions with Cu through the adsorption of small Cu clusters with 1-4 atoms. Moreover, different doping patterns for Ru doping in TaN are investigated to understand how selective doping of the epsilon-TaN surface influences surface stability. We found that an increased concentration of Ru atoms in the outermost Ta layer improves the adhesion of Cu. The strongest binding of the Cu atoms was found on the 100% Ru doped surface followed by 1 ML Ru passivated surface. These two surfaces are recommended for the combined barrier+liner for Cu interconnects. The closely packed arrangements of Cu were found to exhibit weak Cu-slab and strong Cu-Cu interactions, whereas the sparse arrangements of Cu exhibit strong Cu-slab and weak Cu-Cu interactions. The Cu atoms seem to bind more favourably when they are buried in the doped or passivated surface layer due to the increase in their coordination number. This is facilitated by the surface distortion arising from the ionic radius mismatch between Ta and Ru. We also show that the strong Cu-Cu interaction alone cannot predict the association of Cu atoms as a few 2D Cu clusters showed stronger Cu-Cu interaction than the 3D clusters, highlighting the importance of Cu-surface interactions File list (2) download file view on ChemRxiv Ru-TaN-2-final.pdf (4.51 MiB) download file view on ChemRxiv Ru-TaN-2-SI.pdf (2.34 MiB)

Prediction of Co and Ru nanocluster morphology on 2D MoS2 from interaction energies

“…These are (a) a lack of metal–metal bonds, (b) ML rearrangements including incorporation of metal atoms into the S layer and (c) formation of metal–S clusters. Incorporation of adatoms into the surface layer is known to increase the metal–substrate interaction, as is the lack of metal–metal bonds [ 48 ]. A gain in the metal–substrate interaction energy from formation of a metal–S cluster is due to Equation 2 not accounting for this, meaning that energy contributions from the formation of metal–S clusters are included in the metal–substrate interaction energy.…”

“…Based on this understanding, alongside the magnitude of metal-substrate and metal-metal interactions we will be able to predict the morphology of Co and Ru thin films on 2D MoS 2 . We have previously studied 2D and 3D Cu clusters on TaN, where we determined that there are two useful descriptors for 2D-vs-3D growth [48]: (1) If the metal-substrate interaction is more favourable than the metal-metal interaction, then 2D growth is preferred; and (2) if the total binding energy is more favourable than the cohesive energy of the bulk metal, then 2D growth is preferred.…”

Prediction of Co and Ru Nanocluster Morphology on 2D MoS2 from Interaction Energies

“…These are (a) a lack of metal-metal bonds, (b) ML rearrangements including incorporation of metal atoms into the S layer and (c) formation of metal-S clusters. Incorporation of adatoms into the surface layer is known to increase the metal-substrate interaction, as is the lack of metal-metal bonds [47] A gain in the metal-substrate interaction energy from formation of a metal-S cluster is due to Eq. 2 not accounting for this, meaning that energy contributions from the formation of metal-S clusters are included in the metal-substrate interaction energy and thus it cannot be used in a straightforward manner as an indicator of 2D vs 3D growth for these geometries.…”

“…Based on this understanding, alongside the magnitude of metal-substrate and metal-metal interactions we will be able to predict the morphology of Co and Ru thin films on 2D MoS 2 . We have previously studied 2D vs 3D Cu clusters on TaN, where we determined that there are two useful descriptors for 2D vs 3D growth: [47] 1. If the metal-substrate interaction is more favourable than the metal-metal interaction, 2D growth is preferred.…”

Control of Cu morphology on Ru-passivated and Ru-doped TaN Surfaces – promoting growth of 2D conducting copper for CMOS interconnects

“…[3][4][5][6] Otherwise copper tends to form non-conducting islands. [3,7,8] Figure 1: Overview of issues related to downscaling of Cu interconnects and a proposed solution, adapted from Natarajan et al [9] However, as the dimensions of transistor devices decrease, this setup becomes problematic. For example, difficulties arise in depositing two additional layers of material and the Cu interconnect in the high aspect ratio interconnect via.…”