METHOD AND SYSTEM FOR CONTROLLING RESISTIVITY IN INGOTS MADE OF COMPENSATED FEEDSTOCK SILICON
Techniques for controlling resistivity in the formation of a silicon ingot from compensated feedstock silicon material prepares a compensated, upgraded metallurgical silicon feedstock for being melted to form a silicon melt. The compensated, upgraded metallurgical silicon feedstock provides semiconductor predominantly of a single type (p-type or n-type) for which the process assesses the concentrations of boron and phosphorus and adds a predetermined amount of boron, phosphorus, aluminum and/or gallium. The process further melts the silicon feedstock with the boron, phosphorus, aluminum and/or gallium to form a molten silicon solution from which to perform directional solidification and maintains the homogeneity of the resistivity of the silicon throughout the ingot. A balanced amount of phosphorus can be optionally added to the aluminum and/or gallium. Resistivity may also be measured repeatedly during ingot formation, and additional dopant may be added in response, either repeatedly or continuously.
1 . A method for controlling resistivity in the formation of a silicon ingot, comprising the steps of:
preparing a compensated, upgraded metallurgical silicon feedstock for being melted to form a silicon melt, said compensated, upgraded metallurgical silicon feedstock comprising a predominantly p-type semiconductor;
assessing quantitatively the relative concentrations of boron and phosphorus in said compensated, upgraded metallurgical silicon feedstock;
adding to said compensated, upgraded metallurgical silicon feedstock a first greater-than-zero quantity of a first element from the group consisting of boron, aluminum, gallium, mixtures of boron, aluminum and gallium, other Group III elements, phosphorus, or other Group V elements, wherein said quantitatively assessed relative concentrations of boron and phosphorus determine said first greater-than-zero quantity;
melting said upgraded metallurgical silicon feedstock and said first greater-than-zero quantity of said first element to form a molten silicon solution including said first greater-than-zero quantity of said first element;
periodically performing resistivity measurements on said molten silicon solution;
adding to said molten silicon solution a second greater-than-zero quantity of a second element from the group consisting of boron, aluminum, gallium, mixtures of boron, aluminum and gallium, other Group III elements, phosphorus, or other Group V elements, wherein said resistivity determines said greater-than-zero quantity; and
performing a directional solidification of said molten silicon solution for forming a silicon ingot and, by virtue of said adding said first greater-than-zero quantity of said first element and said second greater-than-zero quantity of said second element suppressing the transition of said silicon ingot to n-type material by virtue of reducing the effect of differing boron and phosphorus segregation coefficients.