Diffusion‐Mediated Growth and Size‐Dependent Nanoparticle Reactivity during Ruthenium Atomic Layer Deposition on Dielectric Substrates

Abstract

consisting of two or more alternating self-limiting surface reactions. These selflimiting surface reactions enable thin-film deposition with thickness uniformity over large-area substrates, (sub-) monolayer thickness control, and conformal deposition in 3D structures. [1] During the first ALD cycles the precursors mainly react with the substrate rather than with the ALD-grown material. The surface termination of the substrate can therefore strongly affect the growth behavior during this initial period. [1][2][3] Depending on the nature of the ALD-grown material, the substrate, and the process conditions, ALD can lead to different growth regimes, resulting, for instance, in the deposition of ultrathin continuous films, deposition of highly dispersed nanoparticles, or area-selective deposition. [4] Continuous thin films have a wide variety of applications including nanoelectronics, coatings, and optical components, and their deposition requires either 2D growth or high particle density to achieve fast film closure. Nanoparticles dispersed on a surface are desired for heterogeneous catalysis, and their production requires island-type deposition with a well-defined particle size and particle density. Area-selective deposition can enable nanoscale bottom-up patterning, which allows accurate self-alignment between small features which is difficult to achieve in conventional top-down patterning. [5] To enable area-selective deposition, the growth behavior should be surface-dependent such that the deposition is at the same time favored on designated areas of the substrate and inhibited on others. For each of the aforementioned applications, an understanding of the surface dependence of the initial stages of growth can inform the tailoring of the ALD process to the desired application. [6] ALD of noble metals has received considerable attention because of its potential in applications such as catalysis [7] and nanoelectronic devices. [8] Ruthenium is considered an ideal candidate for novel nanoscale catalysts [9,10] as well as for replacing copper as a conductor in future low-level nano-interconnect structures for integrated circuits. [8] ALD of Ru however presents application-specific challenges. On one hand, nanoparticles of a specific size are desired for high catalytic activity. [10] On Understanding the growth mechanisms during the early stages of atomic layer deposition (ALD) is of interest for several applications including thin film deposition, catalysis, and area-selective deposition. The surface dependence and growth mechanism of (ethylbenzyl)(1-ethyl-1,4-cyclohexadienyl) ruthenium and O 2 ALD at 325 °C on HfO 2 , Al 2 O 3 , OH, and SiOSi terminated SiO 2 , and organosilicate glass (OSG) are investigated. The experimental results show that precursor adsorption is strongly affected by the surface termination of the dielectric, and proceeds most rapidly on OH terminated dielectrics, followed by SiOSi and finally SiCH 3 terminated dielectrics. The initial stages of growth are characterized by the formation a...

Defect Mitigation in Area‐Selective Atomic Layer Deposition of Ruthenium on Titanium Nitride/Dielectric Nanopatterns

“…To understand the impact of nanopatterned substrates on ALD, we first compare the Ru growth behavior on non-patterned surfaces and TiN/SiO2 nanopatterns at 325°C, the high end of the ALD temperature window, to make use of the enhanced Ru growth on TiN [24] and to assess the impact of Ru particle diffusion on dielectrics in nanopatterns. All substrates used in this study are treated with Dimethylamino-Trimethylsilane (DMA-TMS) which selectively inhibits growth on dielectrics by rendering the SiO2 surface -Si(CH3)3 terminated [7,8,22] . Ru ASD on TiN vs SiO2 is achieved on both line and hole patterns, as a Ru film is selectively deposited on TiN while the inhibited growth on SiO2 results in particles (Figure 1a).…”

“…We attribute this to the limited diffusion length of Ru particles compared to the vertical dimensions of the sidewall. Single Ru adatoms have a ~16nm diffusion length, and this diffusion length decreases by a factor k -8/3 for a particle consisting of k atoms [22] . As a result, DMA-TMS/EBECHRu/O2 ASD process produces a uniform layer thickness on TiN which appears independent of feature size over the investigated feature size range.…”

“…Ru adatom deposition is irreversible during EBE-CHRu/O2 ALD, which means that the diffusion length effectively corresponds to the mean free path of a Ru adatom diffusing over the surface before aggregation. While EBECHRu/O2 ALD displays diffusion-mediated growth on dielectric surfaces, the diffusion length is limited (~16nm for single atoms on Si-CH3 terminated dielectrics, and lower for particles consisting of multiple atoms) [22] . As such, the depletion zone is small compared to the 70nm vertical dimension of the SiO2 surface adjacent to the TiN growth surface, and no significant depletion is observed visually in Scanning Electron Microscopy (SEM) for these structures ( Figure 2c).…”

“…Self-Focusing Secondary Ion Mass Spectrometry (SF-SIMS) is well-suited for defect characterization in ASD due to the capability to analyze large patterned areas containing over 10 4 structures, and the superb limit of detection of Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) which ranges between 10 6 -10 11 at cm -2 [16][17][18] . The mechanism of defect formation and growth depends on the deposition process used, and models have been developed for particle growth of both dielectrics [19,20] and metals [21,22] . Since defectivity is a major challenge for ASD uptake in industry, considerable efforts have been made to expand the ASD window, either by prolonging growth inhibition [6,10] , letting defects diffuse from the non-growth to the growth surface [23] , or by removal of defects after ASD [4,15] .…”

“…The surface dependence and growth mechanism of 1-ethylbenzyl-1,4-cyclohexadienylruthenium (EBECHRu)/O2 ALD can be used for Ru ASD on metals with respect to dielectrics. A strategy 2 to mediate defectivity on dielectrics can be proposed based on the growth mechanism during the initial stages of ALD [22] . In the initial stages of Ru growth on Si-CH3 terminated dielectrics, the mechanism is governed by (1) extremely slow deposition of adatoms on the Si-CH3 terminated surface, and (2) diffusion and aggregation of these adatoms into larger particles.…”