Atomic layer deposition of TiO2 on surface modified nanoporous low-k films

Gradient area-selective deposition for seamless gap-filling in 3D nanostructures through surface chemical reactivity control

The integration of bottom-up fabrication techniques and top-down methods can overcome current limits in nanofabrication. For such integration, we propose a gradient area-selective deposition using atomic layer deposition to overcome the inherent limitation of 3D nanofabrication and demonstrate the applicability of the proposed method toward large-scale production of materials. Cp(CH₃)₅Ti(OMe)₃ is used as a molecular surface inhibitor to prevent the growth of TiO₂ film in the next atomic layer deposition process. Cp(CH₃)₅Ti(OMe)₃ adsorption was controlled gradually in a 3D nanoscale hole to achieve gradient TiO₂ growth. This resulted in the formation of perfectly seamless TiO₂ films with a high-aspect-ratio hole structure. The experimental results were consistent with theoretical calculations based on density functional theory, Monte Carlo simulation, and the Johnson-Mehl-Avrami-Kolmogorov model. Since the gradient area-selective deposition TiO₂ film formation is based on the fundamentals of molecular chemical and physical behaviours, this approach can be applied to other material systems in atomic layer deposition.

Ambient pressure x-ray photoelectron spectroscopy setup for synchrotron-based in situ and operando atomic layer deposition research

An ambient pressure cell is described for conducting synchrotron-based x-ray photoelectron spectroscopy (XPS) measurements during atomic layer deposition (ALD) processes. The instrument is capable of true in situ and operando experiments in which it is possible to directly obtain elemental and chemical information from the sample surface using XPS as the deposition process is ongoing. The setup is based on the ambient pressure XPS technique, in which sample environments with high pressure (several mbar) can be created without compromising the ultrahigh vacuum requirements needed for the operation of the spectrometer and the synchrotron beamline. The setup is intended for chemical characterization of the surface intermediates during the initial stages of the deposition processes. The SPECIES beamline and the ALD cell provide a unique experimental platform for obtaining new information on the surface chemistry during ALD half-cycles at high temporal resolution. Such information is valuable for understanding the ALD reaction mechanisms and crucial in further developing and improving ALD processes. We demonstrate the capabilities of the setup by studying the deposition of TiO₂ on a SiO₂ surface by using titanium(IV) tetraisopropoxide and water as precursors. Multiple core levels and the valence band of the substrate surface were followed during the film deposition using ambient pressure XPS.

Comparison of In-Plane Stress Development in Sol-Gel- and Nanoparticle-Derived Mesoporous Metal Oxide Thin Films

By using an evaporation-induced self-assembly (EISA) process, mesoporous metal oxide thin films are prepared via molecular precursors undergoing a sol-gel transition or by using nanoparticle dispersions as the starting materials. Both methods are employed together with PIB₅₀-b-PEO₄₅ as the structure-directing agent to produce porous TiO₂ and ZrO₂ thin films with spherical mesopores of around 14 nm in diameter. These nanoparticle- and sol-gel-derived films were investigated in terms of the intrinsic in-plane stress development during the heat treatment up to 500 °C to evaluate the impact of solvent evaporation, template decomposition and crystallization on the mechanical state of the film. The investigation revealed the lowest intrinsic stress for the nanoparticle-derived mesoporous film, which is assigned to the combination of the relaxing effects of the utilized diblock copolymer and the interparticular gaps between the precrystalline nanoparticles. Furthermore, the residual in-plane stress was studied after annealing steps ranging from 300 to 1000 °C and cooling down to room temperature. Here, TiO₂ nanoparticle-derived mesoporous films possess a lower residual stress than the sol-gel-derived mesoporous films, while in the case of ZrO₂ films, sol-gel-derived coatings reveal the smallest residual stress. The latter is based on the lower thermal expansion coefficient of the dominant monoclinic crystal phase compared to that of the silicon substrate. Hence, the present crystal structure has a strong influence on the mechanical state. The observation in this study helps to further understand the stress-related mechanical properties and the formation of mesoporous metal oxides.

Mobile setup for synchrotron based in situ characterization during thermal and plasma-enhanced atomic layer deposition

We report the design of a mobile setup for synchrotron based in situ studies during atomic layer processing. The system was designed to facilitate in situ grazing incidence small angle x-ray scattering (GISAXS), x-ray fluorescence (XRF), and x-ray absorption spectroscopy measurements at synchrotron facilities. The setup consists of a compact high vacuum pump-type reactor for atomic layer deposition (ALD). The presence of a remote radio frequency plasma source enables in situ experiments during both thermal as well as plasma-enhanced ALD. The system has been successfully installed at different beam line end stations at the European Synchrotron Radiation Facility and SOLEIL synchrotrons. Examples are discussed of in situ GISAXS and XRF measurements during thermal and plasma-enhanced ALD growth of ruthenium from RuO₄ (ToRuS™, Air Liquide) and H₂ or H₂ plasma, providing insights in the nucleation behavior of these processes.

Atomic layer deposition-based tuning of the pore size in mesoporous thin films studied by in situ grazing incidence small angle X-ray scattering

Atomic layer deposition (ALD) enables the conformal coating of porous materials, making the technique suitable for pore size tuning at the atomic level, e.g., for applications in catalysis, gas separation and sensing. It is, however, not straightforward to obtain information about the conformality of ALD coatings deposited in pores with diameters in the low mesoporous regime (<10 nm). In this work, it is demonstrated that in situ synchrotron based grazing incidence small angle X-ray scattering (GISAXS) can provide valuable information on the change in density and internal surface area during ALD of TiO(2) in a porous titania film with small mesopores (3-8 nm). The results are shown to be in good agreement with in situ X-ray fluorescence data representing the evolution of the amount of Ti atoms deposited in the porous film. Analysis of both datasets indicates that the minimum pore diameter that can be achieved by ALD is determined by the size of the Ti-precursor molecule.

Impact of plasma pretreatment and pore size on the sealing of ultra-low-k dielectrics by self-assembled monolayers

Self-assembled monolayers (SAMs) from an 11-cyanoundecyltrichlorosilane (CN-SAM) precursor were deposited on porous SiCOH low-k dielectrics with three different pore radii, namely, 1.7, 0.7, and lower than 0.5 nm. The low-k dielectrics were first pretreated with either O2 or He/H2 plasma in order to generate silanol groups on the hydrophobic pristine surface. Subsequently, the SAMs were chemically grafted to the silanol groups on the low-k surface. The SAMs distribution in the low-k films depends on the pore diameter: if the pore diameter is smaller than the size of the SAMs precursors, the SAM molecules are confined to the surface, while if the pore diameter exceeds the van der Waals radius of the SAMs precursor, the SAMs molecules reach deeper in the dielectric. In the latter case, when the pore sidewalls are made hydrophilic by the plasma treatment, the chemical grafting of the SAM precursors follows the profile of the generated silanol groups. The modification depth induced by the O2 plasma is governed by the diffusion of the oxygen radicals into the pores, which makes it the preferred choice for microporous materials. On the other hand, the vacuum ultraviolet (VUV) light plays a critical role, which makes it more suitable for hydrolyzing mesoporous materials. In addition to the density of the surface -OH groups, the nanoscale concave curvature associated with the pores also affects the molecular packing density and ordering with respect to the self-assembly behavior on flat surfaces. A simple model which correlates the low-k pore structure with the plasma hydrophilization mechanism and the SAMs distribution in the pores is presented.