AVS 60th International Symposium and Exhibition
    Thin Film Monday Sessions
       Session TF+AS+SE+SS-MoA

Paper TF+AS+SE+SS-MoA3
O2 based Ru ALD using CpRu(CO)2Et: First-principles, Experiments and Micro-kinetic Modeling

Monday, October 28, 2013, 2:40 pm, Room 104 A

Session: ALD/MLD Surface Reactions, Precursors, and Properties
Presenter: C.K. Ande, Eindhoven University of Technology, Netherlands
Authors: C.K. Ande, Eindhoven University of Technology, Netherlands
N. Leick, Eindhoven University of Technology, Netherlands
S.D. Elliott, Tyndall National Institute, Ireland
W.M.M. Kessels, Eindhoven University of Technology, Netherlands
Correspondent: Click to Email
In the present work, we use a combination of first-principles calculations, QMS experiments and micro-kinetic modeling to reveal the reactive pathways in operation during an O2 based Ru ALD using CpRu(CO)2Et as the metal precursor. Analysis of the gas phase species in our QMS experiments showed that the surface chemisorption of CpRu(CO)2Et resulted in the formation of dehydrogenation and combustion products such as H2, CO2, CO and H2O. H2 was detected as a major surface reaction product during the metal precursor pulse. Strikingly, during the O2 pulse virtually no H2, H2O or other H-containing reaction products were measured. These results suggest that a number of surfaces might be involved: bare, O-covered Ru and RuO2 surfaces (Leick et al. Chem. Mat., 24, 3696, (2012)).

While it is still experimentally difficult to accurately identify the surface and reactions happening at the surface, Density Functional Theory (DFT) provides an elegant way to study the same. Therefore, we used DFT calculations to study the role of bare and O-covered surfaces on dehydrogenation reactions during the ALD process. Since most of the dehydrogenation occurs from the Et and Cp ligands, as a first step, we studied dehydrogenation of ethane. In order to probe the role of O-covered surfaces in the dehydrogenation reactions, we studied the reactions on both bare (Ru(0001)) and O-covered (0.25 ML and 0.5 ML) Ru surfaces. It is clear from the calculations that the dehydrogenation on the bare Ru(0001) is the most energetically favorable process. Interestingly, they also show that the presence of O on the Ru(0001) surface inhibits the dehydrogenation reactions from taking place. Thus, dehydrogenation reactions happening on O-rich patches of the growing Ru surface can be excluded.

Although DFT calculations provide accurate energy changes and activation energies of each of the possible elementary reactions, they still do not predict the collective behavior when all the processes are possibly happening simultaneously. To resolve this problem we use micro-kinetic modeling and go up to the next higher length and time scales in an ALD process. In micro-kinetic modeling, information about elementary reactions that happen at the gas surface interface is used to describe the overall time evolution of the system which includes species in the gas phase and on the surface. We use accurate activation energies obtained from our DFT calculations in the micro-kinetic model. Preliminary results clearly show the evolution of H2 from the decomposition of ethane. We hope to extend the method and present results about the decomposition of the complete precursor on the bare Ru(0001) surface.