Material evaluation for engineering a novel crucible setup for the growth of oxygen free Czochralski silicon crystals

For manufacturing of several high performance electronic devices, e.g. insulated-gate bipolar transistors (IGBT), single crystalline silicon crystals with high purity and minimum oxygen (in the range of 1015 at/cm3) concentration are required. Such silicon crystals are typically grown by the Floating Zone technique (Fz), as the more common and cheaper Czochralski technique (Cz) uses silica crucible, which leads always to a relatively high oxygen concentration in the silicon crystals (>1017 at/cm-3). Therefore, in this work potential materials were evaluated with respect to the development of a novel oxygen-free crucible system, which should enable a cost effective growth of oxygen free Cz silicon ingots. For that purpose different graphite materials as well as nitride bonded silicon nitride (NSN) were tested in contact with liquid silicon due to their infiltration behaviour and occurrence of crack formation. Functional silicon nitride (Si3N4) coatings were applied by powder based spray coating of reaction bonded silicon nitride (RBSN) and chemical vapour deposition (CVD) on graphite and NSN crucibles. Characterization of the crucible/coating systems before and after crystal growth experiments in a lab-scale casting furnace reveal information about morphology, infiltration behaviour and adhesion strength on the crucible. Further, investigations on the grown silicon crystals give information about impurity incorporation coming from the novel crucible systems. The results indicated, that especially graphite materials with low porosity and a high mechanical strength as well as NSN with polysilazane sealing in combination with a CVD Si3N4 coating have definitely a potential for application as crucible system in silicon growth processes.