In this work, a process for the thermal activated atomic layer deposition (ALD) of ruthenium from the organometallic heteroleptic precursor [(ethylcyclopentadienyl)(pyrrolyl)ruthenium] with molecular oxygen was developed and characterized. Silicon substrates were precleaned in hydrofluoric acid and preheated to a specific temperature before coating with ruthenium. The corresponding cycle-by-cycle growth was monitored throughout the entire ALD process time, utilizing an in-situ real-time spectroscopic ellipsometer. Transmission electron microscopy and atomic force microscopy were applied at a reference sample to generate an appropriate optical model for the translation of the ellipsometric spectra into Ru film thicknesses. Given a representative set of process parameters the cycle-by-cycle growth was studied in detail, obtaining information about incubation, nucleation, linear growth and delamination. In order to determine the ALD characteristic dependencies, the following process parameters were varied while applying ellipsometry during the linear film growth regime on as-deposited ruthenium film surfaces; thus excluding effects from the initial foreign substrate material: both reactant doses and purging times, the substrate temperature and the total pressure. During the respective film growth experiments, one process parameter-setting was changed each 15 ALD cycles, which enabled a fast and extensive process development.
PECVD and PEALD of ruthenium films using RuEtcp 2 as a precursor and N 2 /H 2 /Ar plasma as a reducing agent were characterized. A self-adjusting process to overcome the previously reported inhibition of Ru PEALD on TaN substrates was investigated. Ellipsometric modelling of Ru films was demonstrated providing information on both film thickness and estimated Ru content. The physical properties of PECVD/PEALD Ru films were compared to characteristics of sputtered Ru films within the categories resistivity, impurites, crystal structure, conformity and Cu plating. As a result, ToFSIMS, ERDA and 3D atomprobe revealed the presence of carbon impurities in PECVD and PEALD Ru films, dependent on deposition temperature and plasma power. Nevertheless, highly conductive Ru-C films were produced via PECVD and PEALD achieving resistivities equal to PVD Ru. For all types of Ru films, the size effect played a significant role at thicknesses below 10 nm; Cu plating and crystallization behaviour appeared similar. Direct Cu fill potential of different Ru films was discussed for damascene structures and through silicon vias.
Area selectivity is an emerging sub-topic in the field of atomic layer deposition (ALD), which employs opposite nucleation phenomena to distinct heterogeneous starting materials on a surface. In this paper, we intend to grow Ru exclusively on locally pre-defined Pt patterns, while keeping a SiO substratum free from any deposition. In a first step, we study in detail the Ru ALD nucleation on SiO and clarify the impact of the set-point temperature. An initial incubation period with actually no growth was revealed before a formation of minor, isolated RuO islands; clearly no continuous Ru layer formed on SiO. A lower temperature was beneficial in facilitating a longer incubation and consequently a wider window for (inherent) selectivity. In a second step, we write C-rich Pt micro-patterns on SiO by focused electron-beam-induced deposition (FEBID), varying the number of FEBID scans at two electron beam acceleration voltages. Subsequently, the localized Pt(C) deposits are pre-cleaned in O and overgrown by Ru ALD. Already sub-nanometer-thin Pt(C) patterns, which were supposedly purified into some form of Pt(O ), acted as very effective activation for the locally restricted, thus area-selective ALD growth of a pure, continuous Ru covering, whereas the SiO substratum sufficiently inhibited towards no growth. FEBID at lower electron energy reduced unwanted stray deposition and achieved well-resolved pattern features. We access the nucleation phenomena by utilizing a hybrid metrology approach, which uniquely combines in-situ real-time spectroscopic ellipsometry, in-vacuo x-ray photoelectron spectroscopy, ex-situ high-resolution scanning electron microscopy, and mapping energy-dispersive x-ray spectroscopy.
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