The effect of graphite components and crucible coating on the behaviour of carbon and oxygen in multicrystalline silicon

In the present paper the effect of the furnace interior materials on the carbon and oxygen concentrations in multicrystalline silicon (mc-Si) is studied. Mc-Si ingots were produced in a high-vacuum induction furnace by means of the vertical Bridgman technique. Growth experiments with or without graphite components in the furnace as well as with crucible coatings of different oxygen concentrations were performed. The concentration of carbon monoxide in the growth chamber is found to depend significantly on the setup used. A standard, graphite-containing setup results in pronounced CO formation, which can be completely suppressed by applying graphite-free elements. Oxygen in the crucible coating is shown to influence the concentration of carbon monoxide via the formation of SiO. Growth under a CO enriched atmosphere is associated with the formation of a SiC/SiO2 melt surface layer, which pins the carbon concentration in the melt or crystal near its solubility limit, whereas in graphite- or CO-free growth the dissolved carbon segregates approximately according to Scheil’s law. On the other hand, the effect of carbon monoxide on oxygen concentration in the grown crystals appears to be negligible. Instead, the oxygen concentration is directly related to the oxygen content of the crucible coating.