Process property relations in reactively sputtered transition metal compounds

In the current thesis the relations between the process parameters and the properties of transition metal compound thin films grown by reactive magnetron sputtering techniques are investigated. In the first part, the effect of energetic species, which are generated by backscattering of plasma ions at the target, on the growth and the properties of transition metal nitride films deposition by direct current magnetron sputtering (dcMS) is manifested. Using film and plasma characterization techniques, as well as simulations, it is shown that the energetic bombardment by atomic N species, which are formed by neutralization and backscattering of N2+ ions, leads to growth of CrNx films with high values of compressive stresses and density close to that of the bulk material. Thereupon, the effect of the bombardment by backscattered species on the stress formation and the surface roughness of reactively sputtered VNx films is investigated. Combining results of simulations and experimental findings, it is found that VNx films grown in a N2 rich discharge (N2 flows higher than 20 sccm) exhibit smooth surfaces and high level of compressive stress, as a result of the energetic bombardment by backscattered N species. At N2 flows lower than 20 sccm the impact of backscattered N species is less significant resulting in films with rough surfaces and low compressive stresses. In the second part of the thesis, the issue of the film deposition rate in a newly developed sputtering technique, the high power pulsed magnetron sputtering (HPPMS), is addressed. First, the effect of high of the pulse current and the duty cycle on the deposition rate in HPPMS is investigated. Using a Cr target and the same average target current, deposition rates are compared to dcMS rates. It is found that for a peak target current density, ITpd, of up to 570 mA×cm-2, HPPMS and dcMS deposition rates are equal. For ITpd > 570 mA×cm-2, optical emission spectroscopy shows a pronounced increase of the Cr+/Cr0 signal ratio. In addition, a loss of deposition rate, which is attributed to the self-sputtering, is observed. Based on the latter analysis a theoretical treatment of the deposition process in a non-reactive HPPMS discharge is presented. This leads to the development of a model that describes the deposition rate as a function of process parameters, such as the target voltage, the pulse frequency and the pulse duty cycle. The effect of these parameters on the deposition rate is studied experimentally using carbon, chromium and copper targets. The implementation of the model on the experimental results enables the calculation of the relative fractions of the sputtering gas ions (Ar+) and the sputtered metal ions (M+) in the total ion flux at the target. The M+ content in the target ion current is calculated to adopt values up to ~72% and ~98% for the chromium and the copper targets, respectively. In contrast, the target ion current is found to consist mostly of Ar+ species in the case of the carbon target. The significantly higher fractions of M+ ions for Cr and Cu are attributed to their higher ionization probability and their higher sputtering yield in comparison to C. Finally, the process stability and the deposition rate in reactive HPPMS are studied. It is shown that reactive HPPMS of zirconium oxide exhibits a stable and hysteresis-free transition zone, as opposed to reactive dcMS. The stabilization of the transition zone in HPPMS facilitates the growth of transparent zirconium oxide films at lower target coverage, in comparison to dcMS. The lower target coverage, in turn, allows for film deposition rates up to 2 times higher than those achieved by dcMS. The stabilization of the transition zone is attributed to the higher compound sputtering rate in HPPMS. In the third part, the properties of transition metal compound films grown by HPPMS are studied. As a first case study, TiOx films are deposited from a ceramic TiO1.8 target employing reactive HPPMS and dcMS, for reference. The effect of the peak target current (ITp) on the target and the discharge characteristics, as well as on the film properties is investigated. The increase of ITp is accompanied by an increase of the number of Ti atoms sputtered from the target and an increase in the ionization of the sputtered material. These changes affect the deposition so that the latter is in all cases up to ~40% higher than that achieved by dcMS. The increase of ITp from 2 A to 40 A also results in a drop of the surface roughness, an increase of the film density and an increase of the refractive index. As a second case study, CrN films are deposited reactively by HPPMS and dcMS. Plasma analysis reveals that during HPPMS the ion current towards the growing films is 2 - 3 orders of magnitude higher than that in dcMS. The increased ionization in HPPMS allows for deposition of smooth and dense nanocrystalline CrN films.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2008

Author dc:creator

• Sarakinos, Konstantinos

Contributors dc:contributor

• Wuttig, Matthias

• info:eu-repo/classification/ddc/530
• Sputtern
• Dünne Schicht
• Übergangsmetalllegierung
• Physik
• Magentron sputtering
• transition metal compounds

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

eng

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-112530%22

OAI record oai:identifier

https://publications.rwth-aachen.de/oai2d?verb=GetRecord&metadataPrefix=oai_dc&identifier=oai%3Apublications.rwth-aachen.de%3A49962