Methods for forming single crystal silicon ingots with improved resistivity control
Methods for forming single crystal silicon ingots with improved resistivity control and, in particular, methods that involve gallium or indium doping are disclosed. In some embodiments, the ingots are characterized by a relatively high resistivity.
1. A method for producing a single crystal silicon product ingot from a silicon melt held within a crucible, the method comprising:
adding polycrystalline silicon to the crucible;
heating the polycrystalline silicon to cause the silicon melt to form in the crucible;
adding a first dopant to the crucible, the first dopant being an alloy selected from the group consisting of silicon-gallium and silicon-indium, the silicon melt comprising silicon and the first dopant;
pulling a sample ingot from the silicon melt after adding the alloy, there being a silicon melt comprising silicon and first dopant disposed in the crucible after the sample ingot is pulled;
measuring a resistivity of the sample ingot;
adding an amount of second dopant to the silicon melt comprising silicon and the first dopant after pulling the sample ingot to form a silicon melt comprising silicon, the first dopant and the second dopant, the second dopant being selected from the group consisting of phosphorous and boron, the amount of second dopant added to the silicon melt being based at least in part on the measured resistivity of the sample ingot; and
pulling the single crystal silicon product ingot from the silicon melt comprising silicon, the first dopant and the second dopant after adding the second dopant to the silicon melt.
2. The method as set forth in claim 1 wherein the alloy is silicon-gallium and comprises less than 5 wt % gallium.
3. The method as set forth in claim 1 wherein the alloy is silicon-gallium and a concentration of gallium in the silicon melt after gallium is added to the crucible is less than 0.1 ppma.
4. The method as set forth in claim 1 wherein the alloy is silicon-indium and comprises less than 5 wt % indium.
5. The method as set forth in claim 1 wherein the alloy is silicon-indium and a concentration of indium in the silicon melt after indium is added to the crucible is less than 0.1 ppma.
6. The method as set forth in claim 1 wherein the product ingot has a prime portion with a resistivity of at least about 1,500 Ω-cm.
7. The method as set forth in claim 1 wherein the polycrystalline silicon is semiconductor grade silicon.