In-situ real-time ellipsometric investigations during the atomic layer deposition of ruthenium: A process development from [(ethylcyclopentadienyl)(pyrrolyl)ruthenium] and molecular oxygen

Abstract

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.

Flash-Enhanced Atomic Layer Deposition: Basics, Opportunities, Review, and Principal Studies on the Flash-Enhanced Growth of Thin Films

“…The corresponding growth rates are between 0.11 and 0.64 Å/cycle, and therefore, are in the range reported for the thermal ALD of ruthenium films. 14,17,30 On the contrary, for substrate temperatures above 150…”

“…However, the thermal ALD of ruthenium faces two major challenges. On the one hand, oxygen is utilized as the second reactant, 6,14,16,17 which can lead to the oxidation of the substrate or the underlying film, and thus, to the formation of an undesired parasitic interlayer.…”

“…Knaut et al for example reported a resistivity of about 24 μ cm for a ruthenium film with 11 nm thickness and grown by thermal ALD. 14 The film densities are in the range between 7.4 and 8.0 g/cm 3 as determined by XRR. Figure 12 shows the measured data and simulated curves from XRR analyses of films grown with 300 cycles at substrate temperatures of 125, 150 and 175…”

“…oxygen, may react with the substrate itself leading to the formation of a parasitic interfacial layer. 14,15 In order to prevent this issue a priori, the proper choice of reactants or the use of an alternative deposition technique is essential. Furthermore, many ALD These limitations may be overcome by providing additional energy, e.g.…”

Precursor-surface interactions revealed during plasma-enhanced atomic layer deposition of metal oxide thin films by in-situ spectroscopic ellipsometry

“…In-situ monitoring with resolution of few seconds cannot provide such information, but can permit real-time analysis of the thin film properties by observation of thickness and surface roughness evolution, for example. Well-known as non-destructive, non-contact, and fast optical characterization method, spectroscopic ellipsometry (SE) has been widely employed to study thin films and complex-layered heterostructures with thickness parameters ranging from fractions of Angstroms to several micrometers 38,46,[58][59][60][61][62][63] . Figure 1.…”