Influence of the plasma chemistry and energetics on the composition and structure evolution of sputtered oxide thin films
In the thesis, the relationship between the plasma chemistry and energetics, and the thin film composition and structure evolution of transition metal oxide thin films deposited by magnetron sputtering in an Ar/O2 atmosphere is investigated as a function of the O2 partial pressure (p(O2)). The previously reported composition of films deposited onto grounded non-intentionally heated substrates was correlated with the dominant positive and negative ion populations in the plasma. While the oxygen deficient films were grown in the Ar(+) dominant mode, the close-to-stoichiometric films were grown in the O(+)/O(-) dominant mode. The formation of close-to-stoichiometric ZrO2.1 is observed in the compound mode, while the formation of closed-to-stoichiometric Nb2O4.7 thin films was reported in addition to the compound mode also in the transition mode. This may be understood based on 1.5-1.9 times higher power dissipated in the Nb-Ar-O2 plasma as compared to the Zr-Ar-O2 plasma. It is suggested that at larger power O2 dissociation may be more efficient and lead to the presence of sufficiently high atomic oxygen density to fully oxidize the films. Further, the energy distribution functions (EDF) of O(-) ions of magnetron sputtered Nb, Ta, Zr, and Hf in an Ar/O2 atmosphere were measured as a function of the p(O2). Three ion populations were detected in the plasma: low, medium and high energy ions. The EDFs were compared to distributions obtained based on sputtering theory. If the surface binding energy is assumed to be equal to the heat of formation, good agreement between the experiment and theory was achieved. From correlating the measured ion energy distributions with previously published phase stability data, it can be deduced that large fluxes of medium and high energy O(-) ions may enable the formation of crystalline transition metal oxide thin films during low temperature growth. Furthermore, the EDFs of O(-) ions of magnetron sputtered Al were measured as a function of the p(O2) and the origin of the three ion populations is discussed. Based on calculation, it is proposed that non-sputtered O(-) ions originating from the target surface are accelerated in the cathode fall, while sputtered O(-) ions may be excluded as a significant contribution to the high energy ion population. Moreover, evidence for accelerated sputtered AlO(-) and AlO2(-) clusters is presented, which subsequently dissociate forming a significant part of the detected medium energy O(-) ions. The here presented findings may provide pathways towards deposition rate enhancement through altering the plasma chemistry as well as a phase stability tuning through varying the plasma energetics.
info:eu-repo/classification/ddc/620, composition, mangetron sputtering, plasma chemistry, plasma energetics, structure, thin film oxides, Dünne Schicht, Kristallstruktur, Magnetronsputtern, Oxide, PVD-Verfahren, Plasmachemie, Plasmaenergetik, Zusammensetzung, Ingenieurwissenschaften
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