Methods for determining the resistivity of a polycrystalline silicon melt
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 determining the resistivity of a polycrystalline silicon melt held within a crucible, the method comprising:
pulling a sample rod from the melt;
annealing the sample rod in a thermal donor kill cycle;
applying a current to the sample rod; and
contacting the sample rod with a resistivity probe while applying current to the sample rod to measure the resistivity of the rod.
2. The method as set forth in claim 1 further comprising forming a planar segment on a surface of the sample rod, the resistivity probe contacting the planar segment to measure the resistivity of the rod.
3. The method as set forth in claim 1 wherein the probe is a two-point resistivity probe.
4. 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.
5. 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 100 mm.
6. 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 50 mm.
7. 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.
8. 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 150 mm.
9. 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.
10. The method as set forth in claim 1 wherein the sample rod is secured by a measurement apparatus comprising a clamp that holds the sample rod when contacting the rod with a resistivity probe.
11. The method as set forth in claim 1 wherein the sample rod is annealed prior to measuring the resistivity of the sample rod.
12. The method as set forth in claim 1 further wherein the sample rod is annealed at a temperature of at least about 500° C.
13. The method as set forth in claim 12 wherein a length of the anneal is at least about 5 seconds.
14. The method as set forth in claim 12 wherein a length of the anneal is from about 5 seconds to about 5 minutes.
15. The method as set forth in claim 1 further wherein the sample rod is annealed at a temperature of at least about 650° C.
16. The method as set forth in claim 1 wherein the sample rod has a length of less than about 300 mm.
17. The method as set forth in claim 1 wherein the sample rod has a resistivity of at least about 1,500 Ω-cm.
18. The method as set forth in claim 1 wherein the sample rod has a resistivity of at least about 6,000 Ω-cm.
19. The method as set forth in claim 1 wherein the sample rod has a resistivity of at least about 10,000 Ω-cm.