Dendooven, Jolien

Detavernier, Christophe

Minjauw, Matthias

Rijckaert, Hannes

Van Driessche, Isabel

English

Ghent University Academic Bibliography

Chemical selectivity and nucleation during ALD of Ru with the RuO4 precursor  M. M. Minjauw,a H. Rijckaert,b I. Van Driessche,b C. Detavernier,a J. Dendoovena a Department of Solid State Sciences, COCOON group, Ghent University, Belgium b Department of Chemistry, SCRIPTS group, Ghent University, Belgium  Despite its higher bulk resistivity, ruthenium is proposed to replace copper in sub-10 nm interconnects, because it shows better electromigration behavior and doesn’t need a barrier and liner. We developed thermal and plasma-enhanced ALD processes using RuO4 and H2 that allow for low-temperature deposition of high quality ruthenium thin films [1,2]. Here, we report on the inherent substrate selectivity for the thermal process on H-terminated Si (Si-H) versus SiO₂. In situ spectroscopic ellipsometry (SE) showed a growth delay of 60 cycles on SiO2, while on Si-H growth occurred from the first cycle onward. Fig. 1 presents a cross-section high resolution TEM investigation of a Ru deposition on a patterned Si-H/SiO2 substrate, revealing a smooth, continuous Ru film of 4.5 nm on the Si-H surface, with no growth on SiO2. The chemical selectivity was further investigated in a vacuum cluster tool that allows for direct ‘in vacuo’ sample transfer from the ALD setup to an XPS instrument. The strong oxidative nature of the RuO4-precursor was confirmed to oxidize the Si-H surface, enabling Ru deposition, while no reaction can occur with SiO2. The nucleation on oxide substrates can be enhanced by switching from the thermal process to the plasma-enhanced ALD process [3]. However, in situ grazing incidence small angle X-ray scattering measurements at the synchrotron and ex situ SEM imaging revealed an island-like growth, which is to be avoided if continuous films and low film thicknesses are aimed for. An approach to enhance the nucleation of the RuO₄/H₂-gas process on oxide substrates was developed, based on exposing the surface to trimethylaluminum (TMA) just before the start of the ALD process. As confirmed by in vacuo XPS, the introduction of surface methyl groups during the TMA exposure makes the oxide surface reactive towards RuO4, leading to immediate Ru deposition during the first ALD cycle. The swift nucleation resulted in films with a low roughness and sufficiently low resistivity value, comparable to the Ru thin films deposited on Si-H. Given the high reactivity of TMA, this approach presents a way to achieve Ru metallization of virtually any surface.   [1] M. M. Minjauw et al., J. Mater. Chem. C, 2015, 3, 132. [2] M. M. Minjauw et al., J. Mater. Chem. C, 2015, 3, 4848. [3] J. Dendooven et al., Rev. Sci. Instrum., 2016, 87, 113905.    + Author for correspondence: Jolien.Dendooven@UGent.be Figure 1 HR-TEM image of the Ru film selectively deposited on Si-H with no growth on SiO2 

Chemical selectivity and nucleation during ALD of Ru with the RuO4 precursor

https://biblio.ugent.be/publication/8643020/file/8643021.pdf

Chemical selectivity and nucleation during ALD of Ru with the RuO4 precursor

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Ghent University Academic Bibliography