Method for the production of low defect density silicon
View Patent ↗A process for the preparation of a silicon single ingot in accordance with the Czochralski method. The process for growing the single crystal silicon ingot comprises controlling (i) a growth velocity, v, (ii) an average axial temperature gradient, G 0 , during the growth of a constant diameter portion of the crystal over a temperature range from solidification to a temperature of no less than about 1325° C. to initially produce in the constant diameter portion of the ingot a series of predominant intrinsic point defects including vacancy dominated regions and silicon self interstitial dominated regions, alternating along the axis, and cooling the regions from the temperature of solidification at a rate which allows silicon self-interstitial atoms to diffuse radially to the lateral surface and to diffuse axially to vacancy dominated regions to reduce the concentration intrinsic point defects in each region.
1. A single crystal silicon ingot having a central axis, a seed-cone, an end-cone, and a constant diameter portion between the seed-cone and the end-cone having a lateral surface, a radius, R, extending from the central axis to lateral surface, and an axial length, L, the single crystal silicon ingot, after being grown and cooled from the solidification temperature, having a constant diameter portion comprising multiple axially symmetric regions alternating along the axis of the ingot between a region wherein vacancies are the predominant intrinsic point defect and a region wherein interstitials are the predominant intrinsic point defect, the ingot having at least 2 interstitial dominant regions which are substantially free of agglomerated interstitial defects separated by a vacancy dominant region along the axis of the constant diameter portion of the ingot, wherein the radius of the constant diameter portion of the ingot is at least about 75 mm.
2. The ingot of claim 1 wherein the regions in which crystal lattice vacancies are the predominant intrinsic point defects have a radius, R vac. , extending from the axis of the ingot towards the lateral surface which is at least about 50% of the radius, R, of the constant diameter portion of the crystal.
3. The ingot of claim 1 wherein the regions in which crystal lattice vacancies are the predominant intrinsic point defects have a radius, R vac. , extending from the axis of the ingot towards the lateral surface which is at least about 90% of the radius, R, of the constant diameter portion of the crystal.
4. The ingot of claim 1 wherein each of the regions in which silicon self-interstitial atoms are the predominant intrinsic point defects have an axial length, L int. , which is at least about 25% of the radius, R, of the constant diameter portion of the crystal.
5. The ingot of claim 1 wherein each of the regions in which silicon self-interstitial atoms are the predominant intrinsic point defects have an axial length, L int. , which is less than about twice the radius, R, of the constant diameter portion of the crystal.
6. The process of claim 5 wherein the effective dwell time, t dw-eff. , is less than about 85% of the dwell time required to allow a sufficient quantity of silicon self-interstitial atoms to diffuse to the surface of the ingot only to suppress the concentration of silicon self-interstitial atoms below a critical concentration required for agglomerated intrinsic point defects to nucleate, in an ingot wherein silicon self-interstitial atoms are the predominant intrinsic point defect throughout the entire constant diameter portion of an ingot.
7. The ingot of claim 1 wherein each of the regions in which silicon self-interstitial atoms are the predominant intrinsic point defects have an axial length, L int. , which is about equal to radius, R, of the constant diameter portion of the crystal.
8. The ingot of claim 1 wherein the length of the constant diameter portion of the ingot, L, is at least about 400 mm.
9. The ingot of claim 1 wherein the length of the constant diameter portion of the ingot, L, is at least about 600 mm.
10. The ingot of claim 1 wherein the length of the constant diameter portion of the ingot, L, is at least about 1000 mm.
11. The ingot of claim 1 having a radius of at least about 100 mm.
12. The ingot of claim 1 having a radius of at least about 150 mm.
13. The ingot of claim 1 , wherein L is at least about 400 mm.
14. The ingot of claim 1 , wherein L is at least about 600 mm.
15. The ingot of claim 1 , wherein L is at least about 800 mm.
16. The ingot of claim 1 , wherein L is at least about 1000 mm.
17. The ingot of claim 1 wherein the multiple axially symmetric regions alternating along the axis of the ingot comprises N vac. vacancy dominated regions and N int. silicon self interstitial dominated regions, wherein N vac. is at least 1 and N int. is at least 2, the vacancy dominated regions each having an axial length, L vac. , and a radius, R vac. , extending from the axis of the ingot towards the lateral surface which is at least about 10% of the radius, R, of the constant diameter portion of the crystal, the silicon self-interstitial dominated regions each having an axial length, L int. , and a radial width which is equal to the radius, R, of the constant diameter portion of the silicon single crystal.
18. The ingot of claim 17 wherein the ratio of L vac. /L int. is at least about 0.23.
19. The ingot of claim 17 wherein the ratio of L vac. /L int. is at least about 0.17.
20. The ingot of claim 17 wherein the ratio of L vac. /L int. is at least about 0.14.
21. The ingot of claim 17 wherein the ratio of L vac. /L int. is at least about 0.12.
22. The ingot of claim 17 wherein the ratio of L vac. /L int. is at least about 0.1.
23. The ingot of claim 17 wherein the ratio of L vac. /L int. is at least about 0.08.
24. The ingot of claim 17 wherein N vac. is at least about 2.
25. The ingot of claim 17 wherein N vac. is at least about 4.
26. The ingot of claim 17 wherein N vac. is at least about 6.
27. The ingot of claim 17 wherein N vac. is at least about 8.