ON THE IMPURITY DISTRIBUTION INDUCED BY SURFACE TENSION GRADIENTS: ALUMINUM-DOPED SILICON CYLINDRICAL BARS GROWN FROM A MELT BY THE EFG METHOD

摘要

The edge-defined film-fed growth (EFG) method is the first non-conventional technique for crystalline silicon wafer production to enter into large scale manufacturing in the photovoltaic industry. Molten silicon is an extremely reactive material, where strong thermal forcing in surface-tension-driven flows is realized during the growth process. Using the finite-element technique, the impurity distribution induced by surface tension gradients is determined in aluminum-doped silicon bars grown from the melt by the EFG method. The computed fluid flows reveal three critical Marangoni numbers Ma that determine the impurity distribution as follows: (i) if Ma increases to a certain value Ma_(c1), then the downward flow on the free liquid surface leads to a decrease of the maximum of the dopant concentration C_(max) which is located at the triple point; and (ii) if Ma is larger than Mac1, then turbulence in the fluid flow takes place, which leads to an increase of C_(max).