In-situ analysis on the initial growth of ultra-thin ruthenium films with atomic layer deposition

The initial growth behavior of ruthenium during the thermal-activated atomic layer deposition (ALD) using [(ethylcyclopentadienyl)(pyrrolyl)ruthenium(II)] (ECPR) and molecular oxygen was investigated in a cluster tool combining an ALD reactor with a surface analysis unit under high vacuum conditions. A direct qualification and quantification of the chemical surface composition by X-ray photoelectron spectroscopy (XPS) and a determination of the surface topography by atomic force microscopy (AFM) were conducted in the course of the ALD cycles without vacuum break. XPS revealed a substrate-inhibited Ru growth on a hydrogen-terminated silicon surface, which was preceded by an incubation period of 20 ALD cycles. The Si surface oxidized during the first 50 cycles. AFM measurements showed a roughness maximum around the 40th ALD cycle, which suggested an island growth mode and thus corresponded with the substrate inhibition. As verified from the AFM data with an analytical model by Nilsen et al. the Ru islands coalesced between the 40th and 50th ALD cycle. The ALD growth initiation of Ru was also investigated on aluminum oxide and tantalum nitride. XPS revealed a similarly inhibited growth behavior on all the investigated substrates. However, the ECPR adsorption during the very first Ru precursor pulse differed as the amount of chemisorbed Ru on the NHy-terminated TaNx(O, C) surface was much higher compared to the OH-terminated Al2O3 and the H-terminated Si surface. Summarizing, we demonstrated that in-vacuo XPS and AFM as well as the combination of both are ideally suited for studying the ALD growth initiation of Ru. Furthermore, we provided important chemical information about the initial Ru precursor adsorption on several foreign substrate materials, which will direct further investigations towards a non-inhibited Ru growth.

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► We revealed a substrate-inhibited growth of type 2 characterized by island growth during the ALD of Ru from ECPR and oxygen.
► The island growth caused an increase in roughness as the Ru nuclei served preferred adsorption sites for the ECPR molecules.
► Another unintended effect was the oxidation of the initial substrate material until the Ru islands coalesce.
► Nitrogen or amino surface groups seemed to provide a high sticking coefficient for the ECPR precursor adsorption.
► In-vacuo XPS and AFM provided chemical and structural information about the ECPR adsorption during growth initiation.