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 SiOSi 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 SiOSi and finally SiCH 3 terminated dielectrics. The initial stages of growth are characterized by the formation a...
Area-selective deposition (ASD) is a promising bottom-up manufacturing solution for catalysts and nanoelectronic devices. However, industrial applications are limited as highly selective ASD processes exist only for few materials. “Passivation/deposition/defect removal” cycles have been proposed to increase selectivity, but cycling requires the passivation to be selective to the growth surface as well as the ASD-grown material. Dimethylamino-trimethylsilane (DMA-TMS) can passivate SiO2 surfaces by covering them with −Si(CH3)3 groups. However, the interaction of DMA-TMS with materials other than SiO2 and Si remains largely unknown and its compatibility with cycling is not yet understood. This work investigates the selectivity of metal, nitride, and oxide atomic layer deposition (ALD) to DMA-TMS-passivated SiO2 as well as the surface chemistry and selectivity of the DMA-TMS reaction. The ALD coreagents O2, NH3, and H2O show low reactivity with the −Si(CH3)3-terminated surface at temperatures up to 300 °C, but the selectivity of ALD strongly depends on the metal precursor and temperature. We demonstrate that DMA-TMS is a selective passivation agent for ASD of and on TiO2, TiN, and Ru selective to SiO2, by TiCl4/H2O, TiCl4/NH3, and EBECHRu/O2 ALD, respectively. We investigate the DMA-TMS reaction on Ru and TiN/TiO2 growth surfaces under conditions that passivate SiO2. At least 77% of the area of the growth surface remains reactive for ALD, confirming the compatibility of DMA-TMS with cycling for ASD. We investigate the impact of changes in surface composition due to patterning before ASD and find that DMA-TMS removes F impurities on TiN and TiO2 surfaces. DMA-TMS selectively passivates SiO2 on three-dimensional (3D) nanopatterns, allowing preferential TiO2 deposition on a nonpassivated growth surface. Thus, the selectivity of DMA-TMS shows great promise to expand the ASD material space as well as to increase selectivity during ASD cycles.
Increasing the initial –OH group density on SiO2 surfaces improves dimethylamino-trimethylsilane passivation and increases selectivity for area-selective deposition.
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 H 2 produces smooth films on metal nitrides, and nanoparticles on SiO 2 . The latter form by surface diffusion and aggregation of Ru adspecies. Kinetic modeling shows that changing the surface termination of SiO 2 from −OH to −CH 3 , and thus its surface energy, leads to larger and fewer nanoparticles because of a 1000fold 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 threedimensional (3D) TiN−SiO 2 nanopatterns, which are consistent with Ru migrating from SiO 2 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.
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