Entwicklung von Siliziumnitrid (Si3N4) und Siliziumkarbid (SiC) Beschichtungssystemen durch reaktive Umwandlung von Silizium für die Anwendung in der Halbleitermaterialherstellung und -prozessierung

Silicon nitride Si3N4 as well as silicon carbide SiC are typical ceramic materials which are commonly used for supportive devices during semiconductor production and processing. Due to their chemical and high temperature stability, thermomechanical strength and increased wear resistance these materials are utilized for crucibles, heater exchanger, wafer carriers and heater systems. Nevertheless, the manufacturing of complex and large geometries of solid ceramic materials is expensive and, in some cases, basically not achievable. To mitigate that issue typically isostatic pressed graphite materials, which can be easily machined to complex shapes, is coated with a functional ceramic layer at the surface. This coating has to protect the graphite material against degradation in high temperature and corrosive environment, which are applied during semiconductor production and processing. State of the art coating techniques, like gas phase deposition processes, polymer or powder-based ceramics, are not able to provide homogeneous coatings on complex graphite devices or fulfill not the requirement according to morphology or chemical composition to be used in semiconductor production or processing. For that reason, a novel approach for the formation of Si3N4 as well as SiC coatings on isostatic graphite materials was developed in this work. Therefore, Si3N4 coatings were formed by the reaction-bonded silicon nitride (RBSN) process directly in-situ on the graphite surface, by the conversion of silicon (Si) into Si3N4 after spray application by heat treatment in a nitrogen atmosphere. This results in an increase in the mechanical stability of the RBSN material but with only a minor reduction of porosity. For the formation of a dense SiC coating, on the other hand, the sprayed Si coating was melted in vacuum and infiltrated into the pore structures of the graphite substrate. By optimizing the respective coating systems and the production of multi-layer structures, the surface porosity or the permeability of various graphite materials could be adjusted or completely closed. In addition to pore sealing, a moderation of the coefficient of thermal expansion (CTE) could also be made possible by the defined structure of multi-layer systems, which enables defect-free coating of graphite materials even with increasing CTE difference between substrate and coating. In the final stage the developed Si3N4 and SiC coating systems were tested in lab scale semiconductor production and processing applications. It could be successfully demonstrated that both coating materials showed a high potential for the use especially in silicon crystal growth as well as in SiC or nitride epitaxy.