In semiconductor industries, the surface of silicon wafers are pre-treated with process fluids prior to etching of the integrated circuits. For this purpose, process equipment as commercialised by the industrial partner is used. This equipment positions the silicon discs on a rotating holder and treats the upper disk surface with a feed flow of an etching liquid. The rotation of the disk distributes the liquid uniformly over the surface, but, at the same time, it makes the liquid pinch off the edge of the disk, so that the whole equipment acts as a rotary atomiser. An air flow through the equipment, which is produced for removing toxic gases or vapours produced by the etching process, may transport the liquid droplets into chambers of the equipment which should convey other liquids. This is the source of cross contamination and loss of process fluids. The experimental investigations of this Diploma thesis aim at developing methods for avoiding this contamination and loss by optimising the equipment.