Low defect density silicon having a vacancy-dominated core substantially free of oxidation induced stacking faults
View Patent ↗The present invention relates to a process for preparing a single crystal silicon ingot, as well as to the ingot or wafer resulting therefrom. The process comprises controlling (i) a growth velocity, v, (ii) an average axial temperature gradient, G 0 , and (iii) a cooling rate of the crystal from solidification to about 750° C., in order to cause the formation of a segment having a first axially symmetric region extending radially inward from the lateral surface of the ingot wherein silicon self-interstitials are the predominant intrinsic point defect, and a second axially symmetric region extending radially inward from the first and toward the central axis of the ingot. The process is characterized in that v, G 0 and the cooling rate are controlled to prevent the formation of agglomerated intrinsic point defects in the first region, while the cooling rate is further controlled to limit the formation of oxidation induced stacking faults in a wafer derived from this segment, upon subjecting the wafer to an oxidation treatment otherwise suitable for the formation of such faults.
1. A single crystal silicon wafer having a central axis, a front side and a back side which are generally perpendicular to the axis, a circumferential edge, and a radius extending from the central axis to the circumferential edge of the wafer, the wafer comprising:
an interstitial-dominated, axially symmetric region extending radially inward from the circumferential edge which is substantially free of A type agglomerated interstitial defects; and,
a vacancy-dominated, axially symmetric region extending radially inward from the interstitial-dominated region and containing agglomerated vacancy defects, wherein the concentration of agglomerated vacancy defects is greater than 10 3 defects/cm 3 , and further wherein, upon being subjected to an oxidation treatment, an oxidation induced stacking fault concentration is less than about 50/cm 2 .
2. The wafer of claim 1 wherein the interstitial-dominated, axially symmetric region is also substantially free of B type agglomerated defects.
3. The wafer of claim 1 wherein the wafer has a diameter of at least 150 mm.
4. The wafer of claim 1 wherein the interstitial-dominated, axially symmetric region has a radial width of about 40% of the length of the radius of the ingot.
5. The wafer of claim 1 wherein the interstitial-dominated, axially symmetric region has a radial width of about 60% of the length of the radius of the ingot.
6. The wafer of claim 1 wherein the average oxygen content of the wafer is within the range of about 11 to about 14.5 PPMA.
7. The wafer of claim 1 wherein the average oxygen content of the wafer is within the range of about 14.5 to about 18 PPMA.
8. The wafer of claim 1 wherein the oxidation induced stacking fault concentration of the wafer is less than about 40/cm 2 .
9. The wafer of claim 1 wherein the oxidation induced stacking fault concentration of the wafer is less than about 20/cm 2 .
10. The wafer of claim 1 wherein the oxidation induced stacking fault concentration of the wafer is less than about 10/cm 2 .
11. The wafer of claim 1 wherein the number of light point defects equal to or greater than about 0.12 microns in size on the wafer surface is less than about 25.
12. The wafer of claim 1 wherein the number of light point defects equal to or greater than about 0.12 microns in size on the wafer surface is less than about 10.
13. The wafer of claim 1 wherein the interstitial-dominated, axially symmetric region has a radial width of about 20% of the length of the radius of the ingot.
14. The wafer of claim 1 wherein the interstitial-dominated, axially symmetric region has a radial width of about 80% of the length of the radius of the ingot.
15. The wafer of claim 1 wherein the wafer has a diameter of at least 200 mm.
16. The wafer of claim 15 wherein the interstitial-dominated, axially symmetric region is also substantially free of B type agglomerated defects.
17. The wafer of claim 15 wherein the interstitial-dominated, axially symmetric region has a radial width of about 40% of the length of the radius of the ingot.
18. The wafer of claim 15 wherein the interstitial-dominated, axially symmetric region has a radial width of about 60% of the length of the radius of the ingot.
19. The wafer of claim 15 the average oxygen content of the wafer is within the range of about 11 to about 14.5 PPMA.
20. The wafer of claim 15 wherein the average oxygen content of the wafer is within the range of about 14.5 to about 18 PPMA.
21. The wafer of claim 15 wherein the oxidation induced stacking fault concentration of the wafer is less than about 20/cm 2 .
22. The wafer of claim 15 wherein the number of light point defects equal to or greater than about 0.12 microns in size on the wafer surface is less than about 25.
23. The wafer of claim 1 wherein the wafer has a diameter of at least 300 mm.
24. The wafer of claim 23 wherein the interstitial-dominated, axially symmetric region is also substantially free of B type agglomerated defects.
25. The wafer of claim 23 wherein the interstitial-dominated, axially symmetric region has a radial width of about 40% of the length of the radius of the ingot.
26. The wafer of claim 23 wherein the interstitial-dominated, axially symmetric region has a radial width of about 60% of the length of the radius of the ingot.
27. The wafer of claim 23 wherein the average oxygen content of the wafer is within the range of about 11 to about 14.5 PPMA.
28. The wafer of claim 23 wherein the average oxygen content of the wafer is within the range of about 14.5 to about 18 PPMA.
29. The wafer of claim 23 wherein the oxidation induced stacking fault concentration of the wafer is less than about 20/cm 2 .
30. The wafer of claim 23 wherein the number of light point defects equal to or greater than about 0.12 microns in size on the wafer surface is less than about 25.