Nitrogen-doped silicon substantially free of oxidation induced stacking faults
View Patent ↗A single crystal silicon, ingot or wafer form, which contains an axially symmetric region in which vacancies are the predominant intrinsic point defect, is substantially free of oxidation induced stacking faults and is nitrogen doped to stabilize oxygen precipitation nuclei therein, and a process for the preparation thereof.
1. A single crystal silicon ingot having a central axis, a seed end, an opposite end, and a constant diameter portion between the seed end and the opposite end having a lateral surface and a radius, R, extending from the central axis to the lateral surface, the single crystal silicon ingot being grown from a silicon melt and then cooled from the solidification in accordance with the Czochralski method, the single crystal silicon ingot being characterized in that:
a. the constant diameter portion comprises an axially symmetric region in which vacancies are the predominant intrinsic point defect, the axially symmetric region being generally cylindrical in shape and having a radius, r as , extending from the central axis wherein r as is at least about 0.95 R, the axially symmetric region having a length as measured along the central axis of at least about 20% of the length of the constant diameter portion of the ingot;
b. the axially symmetric region comprises nitrogen at a concentration of about 1×10 13 atoms/cm 3 to about 1×10 15 atoms/cm 3 ; and
c. the axially symmetric region comprises oxygen at a concentration between about 7 ppma and about 10.5 ppma at about 5–6 mm inward of the lateral surface; and
d. the axially symmetric region being substantially free of nuclei which form oxidation induced stacking faults.
2. The single crystal silicon ingot as set forth in claim 1 wherein the axially symmetric region comprises oxygen at a concentration of oxygen of at least about 8–12 ppma at the central axis.
3. The single crystal silicon ingot as set forth in claim 1 wherein the axially symmetric region comprises oxygen at a concentration of about 10 ppma to about 16 ppma at the central axis.
4. The single crystal silicon ingot as set forth in claim 1 wherein the axially symmetric region comprises oxygen at a concentration of about 12 ppma to about 15 ppma at the central axis.
5. The single crystal silicon ingot as set forth in claim 1 wherein the axially symmetric region comprises oxygen at a concentration of about 12.5 ppma to about 14.5 ppma at the central axis.
6. The single crystal silicon ingot as set forth in claim 1 wherein the length of the axially symmetric region is at least about 40% of the length of the constant diameter portion of the ingot.
7. The single crystal silicon ingot as set forth in claim 1 wherein the length of the axially symmetric region is at least about 60% of the length of the constant diameter portion of the ingot.
8. The single crystal silicon ingot as set forth in claim 1 wherein the length of the axially symmetric region is at least about 80% of the length of the constant diameter portion of the ingot.
9. The single crystal silicon ingot as set forth in claim 1 wherein the length of the axially symmetric region is at least about 90% of the length of the constant diameter portion of the ingot.
10. The single crystal silicon ingot as set forth in claim 1 wherein the length of the axially symmetric region is about 100% of the length of the constant diameter portion of the ingot.
11. The single crystal silicon ingot as set forth in claim 1 wherein the constant diameter portion of the ingot has a nominal diameter of at least about 150 mm.
12. The single crystal silicon ingot as set forth in claim 1 wherein the constant diameter portion of the ingot has a nominal diameter of about 200 mm.
13. The single crystal silicon ingot as set forth in claim 1 wherein the constant diameter portion of the ingot has a nominal diameter of about 300 mm.
14. A single crystal silicon ingot having a central axis, a seed end, an opposite end, and a constant diameter portion between the seed end and the opposite end having a lateral surface and a radius, R, extending from the central axis to the lateral surface, the single crystal silicon ingot being grown from a silicon melt and then cooled from the solidification in accordance with the Czochralski method, the single crystal silicon ingot being characterized in that:
a. the constant diameter portion comprises an axially symmetric region in which vacancies are the predominant intrinsic point defect, the axially symmetric region being generally cylindrical in shape and having a radius, r as , extending from the central axis wherein r as is at least about 0.95 R, the axially symmetric region having a length as measured along the central axis of about the length of the constant diameter portion of the ingot;
b. the axially symmetric region comprises nitrogen at a concentration of about 1×10 13 atoms/cm 3 to about 1×10 15 atoms/cm 3 ; and
c. the axially symmetric region comprises oxygen and the concentration of oxygen at the central axis is Oi c , the concentration of oxygen at about 5–6 mm inward of the lateral surface is Oi e , and the radial gradient of oxygen concentration, ORG, given by the formula ORG=(Oi c −Oi e )/Oi c is at least about 15%.
15. The single crystal silicon ingot as set forth in claim 14 wherein the radial gradient of oxygen concentration is about 15% to about 50%.
16. The single crystal silicon ingot as set forth in claim 14 wherein the radial gradient of oxygen concentration is about 20% to about 40%.
17. The single crystal silicon ingot as set forth in claim 14 wherein the radial gradient of oxygen concentration is about 30%.
18. The single crystal silicon ingot as set forth in claim 14 wherein the constant diameter portion has a nominal diameter of about 200 mm.
19. The single crystal silicon ingot as set forth in claim 14 wherein the constant diameter portion has a nominal diameter of about 300 mm.
20. The single crystal silicon ingot as set forth in claim 14 wherein Oi e is about 7 ppma to about 10.5 ppma.
21. A single crystal silicon wafer having a central axis, a front surface and a back surface which are generally perpendicular to the central axis, a circumferential edge, and a radius, R, extending from the central axis to the circumferential edge of the wafer; the wafer being characterized in that:
a. the wafer comprises an axially symmetric region in which vacancies are the predominant intrinsic point defect, the axially symmetric region having a radius, r as , extending from the central axis wherein r as is at least about 0.95 R;
b. the wafer comprises nitrogen at a concentration of about 1×10 13 atoms/cm 3 to about 1×10 15 atoms/cm 3 ;
c. the wafer comprises oxygen and the concentration of oxygen at about 5–6 mm inward of the circumferential edge between about 7 ppma and about 10.5 ppma; and
d. the wafer is substantially free of oxidation induced stacking faults.
22. The single crystal silicon wafer as set forth in claim 21 wherein the concentration of oxygen at about the central axis is at least about 8–12 ppma.
23. The single crystal silicon wafer as set forth in claim 21 wherein the concentration of oxygen at about the central axis is about 10 ppma to about 16 ppma.
24. The single crystal silicon wafer as set forth in claim 21 wherein the concentration of oxygen at about the central axis is about 12 ppma to about 15 ppma.
25. The single crystal silicon wafer as set forth in claim 21 wherein the concentration of oxygen at about the central axis is about 12.5 ppma to about 14.5 ppma.
26. The single crystal silicon wafer as set forth in claim 21 comprising an epitaxial silicon layer on the front surface of the silicon wafer.
27. The single crystal silicon wafer as set forth in claim 26 wherein the epitaxial layer is about 1 μm to about 15 μm thick.
28. The single crystal silicon wafer as set forth in claim 26 wherein the epitaxial layer is about 1 μm to about 10 μm thick.
29. The single crystal silicon wafer as set forth in claim 26 wherein the epitaxial layer is about 1 μm to about 8 μm thick.
30. The single crystal silicon wafer as set forth in claim 26 wherein the epitaxial layer is about 1 μm to about 4 μm thick.
31. A single crystal silicon wafer having a central axis, a front surface and a back surface which are generally perpendicular to the central axis, a circumferential edge, and a radius, R, extending from the central axis to the circumferential edge of the wafer; the wafer being characterized in that:
a. the wafer comprises an axially symmetric region in which vacancies are the predominant intrinsic point defect, the axially symmetric region having a radius, r as , wherein r as is at least about 0.95 R;
b. the wafer comprises nitrogen at a concentration of about 1×10 13 atoms/cm 3 to about 1×10 15 atoms/cm 3 ; and
c. the wafer comprises oxygen and the concentration of oxygen at the central axis is Oi c , the concentration of oxygen at the circumferential edge is Oi e , and the radial gradient of oxygen concentration, ORG, given by the formula ORG=(Oi c −Oi e )/Oi c is at least about 15%.
32. The single crystal silicon wafer as set forth in claim 31 wherein the radial gradient of oxygen concentration is about 15% to about 50%.
33. The single crystal silicon ingot as set forth in claim 31 wherein the radial gradient of oxygen concentration is about 20% to about 40%.
34. The single crystal silicon ingot as set forth in claim 31 wherein the radial gradient of oxygen concentration is about 30%.
35. The single crystal silicon ingot as set forth in claim 31 wherein the radius is about 100 mm.
36. The single crystal silicon ingot as set forth in claim 31 wherein the radius is about 150 mm.
37. The single crystal silicon ingot as set forth in claim 31 wherein Oi e is about 7 ppma to about 10.5 ppma.
38. The single crystal silicon wafer as set forth in claim 31 comprising an epitaxial silicon layer on the front surface of the silicon wafer.