Area-selective deposition (ASD) is a promising bottom-up approach for fabricating nanoelectronic devices. However, a challenge is to prevent the undesired growth of nanoparticles in the nongrowth area. This work uses kinetic Monte Carlo (KMC) methods to investigate the defectivity in ruthenium ASD by (ethylbenzyl)(1-ethyl-1,4-cyclohexadienyl)Ru/O₂ (EBECHRu) atomic layer deposition (ALD) in line-space nanopatterns with different dimensions. Ru ASD is governed by adsorption as well as diffusion. The defectivity depends on the pattern dimensions, as nanoparticles can diffuse and reach the interface with the growth area where they aggregate. For linewidths of 50 nm and smaller, all Ru adspecies are captured at the growth interface before growth by precursor adsorption is catalyzed. The synergetic effect of diffusion and size-dependent reactivity reduces defectivity below 10¹⁰ Ru atoms cm⁻² for at least 1000 ALD cycles. This is more than 1000 times lower than for patterns with a linewidth of 200 nm and larger, where the Ru content decreases significantly only near the interface with the growth surface. The predicted depletion zone is confirmed by experiments in nanoscale line-space patterns. Overall, this mechanism results in smaller and fewer Ru nanoparticles for smaller patterns, facilitating the development of passivation-deposition-etch ASD processes for nanoelectronic device fabrication.

Area-selective deposition (ASD) enables the growth of materials on target regions of patterned substrates for applications in fields ranging from microelectronics to catalysis. Selectivity is often achieved through surface modifications aimed at suppressing or promoting the adsorption of precursor molecules. Here, we show instead that varying the surface composition can enable ASD by affecting surface diffusion rather than adsorption. Ru deposition from (carbonyl)-(alkylcyclohexadienyl)Ru and H2 produces smooth films on metal nitrides, and nanoparticles on SiO2. The latter form by surface diffusion and aggregation of Ru adspecies. Kinetic modeling shows that changing the surface termination of SiO2 from -OH to -CH3, and thus its surface energy, leads to larger and fewer nanoparticles because of a 1000-fold increase in surface diffusion rates. Kinetic Monte Carlo simulations show that even surface diffusion alone can enable ASD because adspecies tend to migrate from high- to low-diffusivity regions. This is corroborated by deposition experiments on three-dimensional (3D) TiN-SiO2 nanopatterns, which are consistent with Ru migrating from SiO2 to TiN. Such insights not only have implications for the interpretation of experimental results but may also inform new ASD protocols, based on chemical vapor and atomic layer deposition, that take advantage of surface diffusion.

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 O₂ ALD at 325 °C on HfO₂, Al₂O₃, OH, and SiOSi terminated SiO₂, 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CH₃ terminated dielectrics. The initial stages of growth are characterized by the formation and growth of Ru nanoparticles, which is mediated by the diffusion of Ru species. Mean-field and kinetic Monte Carlo modeling show that ALD on OSG is best described when accounting for (1) cyclic generation of new nanoparticles at the surface, (2) surface diffusion of both atomic species and nanoparticles, and (3) size-dependent nanoparticle reactivity. In particular, the models indicate that precursor adsorption initially occurs only on the dielectric substrate, and occurs on the Ru nanoparticles only when these reach a critical size of about 0.85 nm. This phenomenon is attributed to the catalytic decomposition of oxygen requiring a minimum Ru nanoparticle size.