Field assisted sintering of yttria ceramics for plasma etching applications

Advanced ceramics materials like yttrium oxide (Y$_{2}$O$_{3}$) are of high interest for critical manufacturing processes in the semiconductor industry due to their high chemical stability in contact with fluorine based etching plasmas. However, until now Y$_{2}$O$_{3}$ gets primarily applied as a functional coating deposited by thermal spray or aerosol deposition technique due to complications associated with the manufacturing of bulk ceramic components. Yttria exhibits a low sinterability when conventionally processed and fabricating large scale samples with high performance concerning chemical purity and relative density is a challenging task. Complex processing routes using conventional or vacuum sintering and an additional post-compaction step by hot isostatic pressing are necessary to achieve relative densities which are matching the requirements of the semiconductor industry. These major drawbacks have prevented the application of bulk Y$_{2}$O$_{3}$ components in state of the art semiconductor manufacturing devices. Therefore, in this work, field assisted sintering technique /spark plasma sintering (FAST/SPS) is investigated as a straight forward processing technique which enables to consolidate high performance, dense ceramic components in a single processing step. In two separate parts, applied and fundamental research questions are going to be addressed. The first part of this work focuses on evaluating the direct processability of commercial powders, solving challenges during the upscaling of sample sizes, processing of complex shaped components as well as characterizing the impact of rare earth doping on sintering and grain growth. Upscaling of ceramic samples is generally hindered by the formation of thermal inhomogeneities in the tool setup. Therefore the application of carbon fibre reinforced carbon spacers and their optimal position in the FAST/SPS tool was investigated by coupling experiments and simulations. Furthermore, graphite powder bed assisted FAST/SPS was applied to study the possibilities of sintering multiple complex shaped Y$_{2}$O$_{3}$ samples in one step. Lastly, the influence of rare earth doping with La$^{3+}$ and Gd$^{3+}$ on sintering and grain growth of Y$_{2}$O$_{3}$ during FAST/SPS processing was studied thoroughly. The segregation of La$^{3+}$ decelerated both sintering and grain boundary kinetics through a solute drage ffect, effectively preventing pore detachment at high sintering temperatures and leading to enhanced densification in the final stage of sintering. [...