Hoex, B.; Heil, S.B.S.; Langereis, E.; van de Sanden, M.C.M.; Kessels, W.M.M.

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Basics of ALD Atomic layer deposition (ALD) is a low temperature vapor-based deposition technique for ultrathin and conformal film growth with submonolayer growth control use saturative surface reactions to ensure self-limiting film growth

Reaction mechanisms during plasma-assisted atomic layer deposition (ALD) of Al2O3 from Al(CH3)3 and O2 plasma were studied by time-resolved quartz crystal microbalance measurements, mass spectrometry, and optical emission spectroscopy. Al(CH3)3 chemisorption on the oxide surface after the plasma pulse releases CH4 products while from the detection of CO, CO2, and H2O in the O2 plasma it is established that surface –CH3 groups are predominantly removed by O radical-driven combustionlike reactions. Also a second pathway exists for –CH3 removal driven by H2O generated in this plasma step. These reaction pathways are expected to be generic for plasma-assisted ALD of oxides from metal organic precursors.

Plasma-assisted atomic layer deposition ͑ALD͒ of metal oxide films is increasingly gaining interest, however, the underlying reaction mechanisms have rarely been addressed. In this work, a case study is presented for the plasma-assisted ALD process of Al 2 O 3 based on Al͑CH 3 ͒ 3 dosing and O 2 plasma exposure. A complementary set of time-resolved in situ diagnostics was employed, including spectroscopic ellipsometry, quartz crystal microbalance, mass spectrometry, and optical emission spectroscopy. The saturation of the Al͑CH 3 ͒ 3 adsorption reactions was investigated, as well as the reaction products created during both the precursor dosing and the plasma exposure step. The generality of the observations was cross-checked on a second commercial ALD reactor. The main observations are as follows: ͑i͒ during the precursor dosing, the Al͑CH 3 ͒ 3 predominantly binds bifunctionally to the surface at 70°C through a reaction in which H is abstracted from the surface and CH 4 is released into the gas phase; ͑ii͒ during the plasma exposure, O radicals in the plasma are consumed at the surface by combustionlike reactions with the surface −CH 3 ligands, producing mainly H 2 O, CO 2 , and CO; ͑iii͒ small gas phase densities of CH 4 and higher hydrocarbons ͑C 2 H x ͒ are also present during the O 2 plasma exposure step indicating complementary surface reactions including a secondary thermal ALD-like reaction by the H 2 O produced at the surface; ͑iv͒ the plasma and its optical emission are strongly affected by the surface reaction products released in the plasma. In the latter respect, optical emission spectroscopy proved to be a valuable tool to study the surface reaction products during the plasma exposure as well as the saturation of the surface reactions. The implications of the experimental observations are addressed and it is discussed that the reaction mechanisms are generic for plasma-assisted ALD processes based on metal organic precursors and O 2 plasma as oxidant source.

DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal. If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the "Taverne" license above, please follow below link for the End User Agreement:

Heil, S.B.S.; Langereis, E.; Roozeboom, F.; van de Sanden, M.C.M.; Kessels, W.M.M.

The growth of ultrathin TiN films by plasma-assisted atomic layer deposition (PA-ALD) was studied by in situ spectroscopic ellipsometry (SE). In between the growth cycles consisting of TiCl4 precursor dosing and H2–N2 plasma exposure, ellipsometry data were acquired in the photon energy range of 0.75–5.0eV. The dielectric function of the TiN films was modeled by a Drude-Lorentz oscillator parametrization, and the film thickness and the TiN material properties, such as conduction electron density, electron mean free path, electrical resistivity, and mass density, were determined. Ex situ analysis was used to validate the results obtained by in situ SE. From the in situ spectroscopic ellipsometry data several aspects related to thin film growth by ALD were addressed. A decrease in film resistivity with deposition temperature between 100 and 400°C was attributed to the increase in electron mean free path due to a lower level of impurities incorporated into the films at higher temperatures. A change in resistivity and electron mean free path was observed as a function of film thickness (2–65nm) and was related to an increase in electron-sidewall scattering for decreasing film thickness. The TiN film nucleation was studied on thermal oxide covered c-Si substrates. A difference in nucleation delay was observed on these substrates and was related to the varying surface hydroxyl density. For PA-ALD on H-terminated c-Si substrates, the formation of an interfacial SiNx film was observed, which facilitated the TiN film nucleation.