The materials utilised in the production of Si wafers must for this reason meet maximum requirements with regard to their purity. This naturally applies to all parts and components used during the following process steps for further processing of wafers. These components should also exhibit a high degree of temperature and chemical resistance and good thermal conductivity. Due to these reasons, the solar industry utilises practically only quartz glass, graphite, CFC composite materials and coated ceramics. Crucibles, for example, which are used to hold the melted ultra-pure silicon during crystal drawing or casting are made of quartz glass and supported by crucibles manufactured from carbon fibre reinforced carbon. Graphite or CFC heating elements fixed with CFC screws are used for heating, due to their extremely high purity. Evaporators utilised for applying coatings after wafer production are also made of these materials.