Thermodynamical analysis of oxygen incorporation from a quartz crucible during solidification of multicrystalline silicon for solar cell

We proposed an oxygen transport model in which the reaction between a liner made of Si₃N₄ and a crucible made of SiO₂ was taken into account to study the mechanism of oxygen incorporation in multicrystalline silicon for a solar cell grown by the unidirectional solidification method. The equilibrium oxygen concentration in the case of the unidirectional solidification method was calculated by taking into account the two interfaces between a quartz crucible and a liner of Si₃N₄ and between a liner of Si₃N₄ and silicon melt. The calculated equilibrium oxygen concentration was less than half of that in the case of the Czochralski method, in which oxygen was directly dissolved from a quartz crucible into the melt. We also calculated the distribution of oxygen concentration in a silicon crystal by using numerical calculation with global modeling. The equilibrium concentrations of oxygen in the two cases were used as boundary conditions at the interface between silicon melt and quartz crucible in the numerical calculation. The results of numerical calculation by taking into account the Si₃N₄ coating were found to be close to the experimental results. From these results, we concluded that oxygen was incorporated from a quartz crucible into the melt through the coating material of Si₃N₄ during the growth process.