Thin Film Growth using Pulsed and Highly Ionized Vapor Fluxes
Sammanfattning: Microstructure and morphology of thin films are decisive for many of their resulting properties. To be able to tailor these properties, and thus the film functionality, a fundamental understanding of thin film growth needs to be acquired. Film growth is commonly performed using continuous vapor fluxes with low energy, but additional handles to control growth can be obtained by instead using pulsed and energetic ion fluxes. In this licentiate thesis the physical processes that determine microstructure and morphology of thin films grown using pulsed and highly ionized vapor fluxes are investigated.The underlying physics that determines the initial film growth stages (i.e., island nucleation, island growth and island coalescence) and how they can be manipulated individually when using pulsed vapor fluxes have previously been investigated. Their combined effect on film growth is, however, paramount to tailor film properties. In the thesis, a route to generate pulsed vapor fluxes using the vapor-based technique high power impulse magnetron sputtering (HiPIMS) is established. These fluxes are then used to grow Ag films on SiO2 substrates. For fluxes with constant energy and deposition rate per pulse it is demonstrated that the growth evolution is solely determined by the characteristics of the vapor flux, as set by the pulsing frequency, and the average time required for coalescence to be completed.Highly ionized vapor fluxes have previously been used to manipulate film growth when deposition is performed both normal and off-normal to the substrate. For the latter case, the physical mechanisms that determine film microstructure and morphology are, however, not fully understood. Here it is shown that the tilted columnar microstructure obtained during off-normal film growth is positioned closer to the substrate normal as the ionization degree of the flux increases, but only if certain nucleation characteristics are present.
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