Interfacial phenomena of molten silicon: Marangoni flow and surface tension

Temperature oscillation due to the oscillatory Marangoni flow was measured for a molten half-zone silicon column (10 mm high and 10 mm in diameter with a temperature difference of 150K between the upper and lower solid-liquid interfaces) under microgravity by using fine thermocouples. The flow is in a hypercritical condition; that is, the Marangoni number is estimated to be over 10000. The structure of the Marangoni instability is two-fold symmetry for the small aspect ratio (height/radius) Γ of 1 and one-fold symmetry for the melt with Γ of 2. The surface tension of molten silicon was measured by a sessile drop method in carefully controlled ambient atmospheres with various oxygen partial pressures from 4 × 10-22 to 6 × 10-19 MPa. These measurements showed that the surface tension and its temperature coefficient showed a marked dependence on oxygen partial pressure. Accordingly the effect of oxygen partial pressure on the Marangoni flow should be made clear. Moreover, Marangoni flow at the flat surface, which corresponds to the flow for the Czochralski growth system, should also be studied.