Effect of Impurity Doping on Density Anomalies in Molten Silicon

Abstract

The density of molten silicon doped with 0.1 at% boron or 0.1 at% gallium was measured over a temperature range from the melting point to 1650° C by using an improved Archimedean method with modified dipping procedure to study the influence of impurity doping on density anomaly. Density anomaly with the thermal volume expansion coefficient of about 8.0×10-4 K-1 has been observed from 1420° C to 1435° C for the pure molten silicon, together with the drasric decrease in density, regarded as the stage prior to solidification, from the melring temperature to 1420° C. This anomaly was also observed in 0.1 at% boron-doped silicon melt, but completely suppressed in 0.1 at% gallium-doped melt. No change was observed, however, in the thermal volume expansion coefficient, which remained about 0.6×10-4 K-1, regardless of the addition of such impurities over 1435° C. Concentration dependence of density anomalies was also investigated using the molten silicon doped with 0.1-1.0 at% gallium, showing no sign of the anomalous temperature coefficient.

Thermophysical Properties of Molten Silicon

“…The temperature dependence of density measured using an electrostatic levitator appears to follow a quadratic function, whereas density measured by other methods shows a linear relationship against temperature. Although the existence of anomalies of thermophysical properties just above the melting temperature had been reported by the Kimura Meta Melt Project [16,24,25] as shown in Fig. 4.7, this was not confirmed in other measurements in the wide temperature range including the undercooled condition, i.e.…”

A melt clusterization within the interfacial boundary layer and its hydrodynamics modelling at the microgravity semiconductor single crystal growth

“…The similar extreme temperature points reflecting in macroscale the process of melt self-ordering are accompanied with the significant changes in thermophysical properties of silicon melt. In this respect the best known are, probably, results of Kimura Meta Melt Project [7][8][9]. An anomalous density jump with the magnitude depending on initial doping nature was found near the melting point of Si.…”

“…Finally, the mathematical model of heat-mass transfer for the whole area, where the crystallization process takes place, includes Eqs. (1), (3), (7), (8) in which the temperature T and values of r; l; C p ; D; L ; S are single-valued and continuous one-variable functions of the enthalpy h.…”