Negative oxygen ion formation in reactive magnetron sputtering processes for transparent conductive oxides

Abstract

Reactive d.c. magnetron sputtering in Ar/O2 gas mixtures has been investigated with energy-resolved mass spectrometry. Different metal targets (Mg, Ti, Zn, In, InSn, and Sn), which are of importance for transparent conductive oxide thin film deposition, have been used to study the formation of negative ions, mainly high-energetic O−, which are supposed to induce radiation damage in thin films. Besides their energy distribution, the ions have been particularly investigated with respect to their intensity in comparison of the different target materials. To realize the comparability, various calibration factors had to be introduced. After their application, major differences in the negative ion production have been observed for the target materials. The intensity, especially of O−, differs by about two orders of magnitude. It is shown that this difference results almost exclusively from ions that gain their energy in the target sheath. Those may gain additional energy from the sputtering process or reflection at the target. Low-energetic negative ions are, however, less affected by changes of the target material. The results concerning O− formation are discussed in term of the sputtering rate from the target and are compared to models for negative ion formation.

Influence of ionisation zone motion in high power impulse magnetron sputtering on angular ion flux and NbOxfilm growth

“…This explains the appearance of the peak at ∼300 eV in the IEDFs of O − which result from O − 2 ions that were dissociated, most likely in a collision with an electron, into a neutral O atom and an O − ion equally sharing the initial energy of the molecular ion. Other contributions from dissociated NbO − x ions, similar to metal-oxygen ions reported in [38][39][40][41], were not recorded and such ions are absent in the studied discharge within the sensitivity of the measurement.…”

A review comparing cathodic arcs and high power impulse magnetron sputtering (HiPIMS)

“…Renucleation occurs due to ion-induced defects, and the average grain size is reduced. As a consequence, films are less conducting and more absorbing, which is of special concern for transparent conducing oxides [238][239][240]. Both positive and negative ions have an effect on texture and phase formation, e.g.…”

Tracing the 5000-year recorded history of inorganic thin films from ∼3000 BC to the early 1900s AD

“…The negative ions, accelerated by the same potential used to produce sputtering by positive ions incident at the target, bombard the growing film with energies that can be sufficiently high to produce residual defects and material loss by resputtering. [169][170][171] Practical applications for sputter-deposited single and multi-layer metal films used as mirrors and optical coatings on telescope lenses and eyepieces were discussed in papers published in 1877 by A. W. Wright, Yale University. 172,173 He reported the growth of adherent noble-metal films sputter-deposited from wire targets onto glass microscope slides.…”