Crystal growth and resistivity modulation of n-type phosphorus-doped cast mono-like silicon

Resistivity tailing seriously reduces the production of phosphorus-doped n-type cast mono-like silicon (CM-Si) ingots and increases costs. However, it is believed that a uniform axial dopant profile can be efficiently obtained by adjusting furnace pressure to enhance phosphorus evaporation at the ingot top due to high saturated vapor pressure of phosphorus in molten silicon. To increase the resistivity at the ingot top, we compared the growth of n-type cast mono-like silicon ingots under normal and reduced pressure. Ingots quality was characterized, and resistivity distribution was measured and discussed. The fitting results of resistivity suggest that Scheil's equation which describes the solute redistribution during the non-equilibrium solidification process of the crystals can be used to calculate theoretical resistivity distribution of lightly phosphorus-doped ingots under normal furnace pressure (600 mbar), but it need to be modified in depressurization process. The modified results shows that the physical growth under reduced pressure is a coupling result of evaporation and segregation, of which a model to calculate the mass transfer coefficients of phosphorus in silicon is established. The obtained mass transfer co-efficients illustrate that the transfer of phosphorus through gas phase to external environment is the controlling step, and depressurization can enhance the evaporation of phosphorus to a certain extent by increasing the total mass transfer coefficient. This work is supposed to pave an economy-effective way to fabricating n-type CM-Si ingots with homogenized axial resistivity profile in industry.