Sample rod growth and resistivity measurement during single crystal silicon ingot production
Methods for forming single crystal silicon ingots with improved resistivity control. The methods involve growth and resistivity measurement of a sample rod. The sample rod may have a diameter less than the diameter of the product ingot. The resistivity of the sample rod may be measured directly by contacting a resistivity probe with a planar segment formed on the sample rod. The sample rod may be annealed in a thermal donor kill cycle prior to measuring the resistivity.
1. A method for producing a single crystal silicon ingot from a silicon melt held within a crucible comprising:
adding polycrystalline silicon to the crucible;
heating the polycrystalline silicon to cause a silicon melt to form in the crucible;
pulling a sample rod from the melt, the sample rod having a diameter;
annealing the sample rod to annihilate thermal donors;
measuring a resistivity of the sample rod after annihilation of thermal donors; and
pulling a product ingot from the melt, the product ingot having a diameter, the diameter of the sample rod being less than the diameter of the product ingot.
2. The method as set forth in claim 1 wherein a resistivity of the sample rod is measured by contacting the rod with a resistivity probe.
3. The method as set forth in claim 1 wherein a resistivity of the sample rod is measured without slicing the sample rod into wafers or slugs.
4. The method as set forth in claim 1 further comprising forming a planar segment on the sample rod, a resistivity of the sample rod being measured on the planar segment.
5. The method as set forth in claim 4 wherein the planar segment extends axially from one end of the sample rod toward a second end of the sample rod.
6. The method as set forth in claim 4 wherein a probe is contacted with the planar segment to measure a resistivity of the sample rod.
7. The method as set forth in claim 1 further comprising applying a current to the sample rod to measure a resistance of the sample rod.
8. The method as set forth in claim 1 wherein the diameter of the sample rod is less than 0.75 times the diameter of the product ingot.
9. The method as set forth in claim 1 wherein the sample rod has an average diameter, the average diameter of the sample rod being less than about 150 mm.
10. The method as set forth in claim 1 wherein the sample rod has a largest diameter, the largest diameter of the sample rod being less than about 50 mm.
11. The method as set forth in claim 1 wherein the sample rod has a length of less than about 300 mm.
12. The method as set forth in claim 1 wherein the product ingot has a resistivity of at least about 1,500 Ω-cm.
13. The method as set forth in claim 1 wherein the sample rod has a resistivity of at least about 1,500 Ω-cm.
14. The method as set forth in claim 1 comprising determining an average resistivity of the sample rod.
15. The method as set forth in claim 14 wherein the sample rod is secured by a measurement apparatus comprising a clamp that holds the sample rod while contacting the sample rod with a resistivity probe.
16. The method as set forth in claim 1 further wherein the sample rod is annealed at a temperature of at least about 500° C.
17. The method as set forth in claim 1 wherein a length of the anneal is at least about 5 seconds.
18. The method as set forth in claim 1 wherein the sample rod has an average diameter, the average diameter of the sample rod being less than about 25 mm.