Atomic Layer Deposition of Ruthenium on Ruthenium Surfaces: A Theoretical Study

Abstract

Atomic layer deposition (ALD) of ruthenium using two ruthenium precursors, i.e., Ru(C 5 H 5 ) 2 (RuCp 2 ) and Ru(C 5 H 5 )(C 4 H 4 N) (RuCpPy), is studied using density functional theory. By investigating the reaction mechanisms on bare ruthenium surfaces, i.e., (001), (101), and (100), and H-terminated surfaces, an atomistic insight in the Ru ALD is provided. The calculated results show that on the Ru surfaces both RuCp 2 and RuCpPy can undergo dehydrogenation and ligand dissociation reactions. RuCpPy is more reactive than RuCp 2 . By forming a strong bond between N of Py and Ru of the surface, RuCpPy can easily chemisorb on the surfaces. The reactions of RuCp 2 on the surfaces are less favorable as the adsorption is not strong enough. This could be a factor contributing to the higher growth-per-cycle of Ru using RuCpPy, as observed experimentally. By studying the adsorption on H-terminated Ru surfaces, we showed that H can prevent the adsorption of the precursors, thus inhibiting the growth of Ru. Our calculations indicate that the H content on the surface can have an impact on the growth-percycle. Finally, our simulations also demonstrate large impacts of the surface structure on the reaction mechanisms. Of the three surfaces, the (100) surface, which is the less stable and has a zigzag surface structure, is also the most reactive one.

Classification of processes for the atomic layer deposition of metals based on mechanistic information from density functional theory calculations

“…Similar ligand dissociation reactions are linked to high rates of metal ALD in the case of cyclopentadienyl-based Ru precursors. 23 We thus get a picture of metal precursors adsorbing onto the electron-rich metallic surface during step 1b of growth, with the valence electronic states from the substrate extending over the adsorbate metal atoms, and ligands being transferred to substrate atoms. The net effect is partial oxidation of substrate atoms and reduction of the adsorbate metal centers.…”

Modeling Mechanism and Growth Reactions for New Nanofabrication Processes by Atomic Layer Deposition

“…[ 87 ] On the basis of all these fi ndings, we propose metallocenes MCp 2 , where M(II) is an oxidisable transition metal cation, as possible reducing co-reagents for Cu ALD, and use quantum chemical calculations and solution phase experiments to evaluate the most promising metal M. [ 88 ] Phung et al contribute to the understanding of ALD of ruthenium in their DFT studies. [ 11,89 ] They study the adsorption of two different precursors, RuCp 2 and RuCpPy [Cp = C 5 H 5 , Py = C 4 H 4 N] on a TiN substrate using a vdW inclusive DFT method. They fi nd that that the RuCpPy precursor chemisorbs on the TiN(100) surface while the RuCp 2 precursor only physisorbs.…”

“…[ 11 ] By contrast, on ruthenium surfaces, it is seen that both RuCp 2 and RuCpPy undergo ligand dissociation reactions. [ 89 ] Alkyl ligands are a part of many organometallic precursors for metal ALD, and so it is useful to understand their adsorption and dissociation behavior on metal substrates, which is also important for a variety of catalytic processes. To this end, Ande et al study all possible elementary reactions involved in the interaction of CH 4 , C 2 H 6 , C 2 H 4 and C 2 H 2 with the Ru(0001) surface using DFT calculations.…”

“…A few recent theoretical works therefore use a vdW inclusive DFT method when studying the adsorption of precursors and their surface reactions. [ 11,79,89,107 ] We calculate the adsorption energies of the copper precursor Cu(dmap) 2 on Cu surfaces using several vdW inclusive DFT methods along with pure DFT. [ 79 ] We fi nd that, despite their small magnitude per atom, vdW interactions play an important role in the adsorption geometries and energies of the precursor on smooth Cu surfaces.…”

Electrical Properties of ZrO2/Al2O3/ZrO2‐Based Capacitors with TiN, Ru, and TiN/Ru Top Electrode Materials

“…In this regard, Ru is a highly promising candidate as a top electrode of the immediate next‐generation DRAM capacitor because the atomic layer deposition (ALD) process of Ru has been extensively developed and its feasible properties as a capacitor top electrode even with a thickness down to 2–3 nm have been confirmed . Ru also has a higher work function (≈4.7 eV) than TiN (≈4.3 eV), which can help solve the leakage problem .…”