In the semiconductor industry, plasma etching processes are widely used. Process chamber parts that are located in the plasma etching system are also exposed to the harsh environmental conditions. Thus, parts located close to the process area are typically coated with yttria to increase service life, and thus process performance. However, such yttria coatings are usually porous, and thus can be attacked by fluorine containing plasma. In order to increase the lifetime of the components in the plasma etching system, this research project aimed to improve the protective yttria layer by reducing the porosity of the protective layer. Specifically, a design of experiment was employed in which the porosity was the target value. The main effects of the coating parameters and their interactions including the surface treatment before the coating process were determined. Furthermore, the bonding of the protective coating to the component to be protected, as well as the element distribution and the coating morphology were investigated. The results and their ramifications with respect to the envisaged application will be discussed.