Silicon structures with improved resistance to radiation events
A silicon structure with improved protection against failures induced by excess radiation-induced charge carrier migration from the bulk region into the near-surface region. The structure comprises bulk and near-surface regions that are doped with a dopant, wherein the concentration in the near-surface region is at least 10 times the maximum concentration, c, of dopant in the bulk region. The structure further comprises a transition region between the bulk and near-surface regions extending less than about 1 μm from the near-surface region toward the central plane.
1. A silicon structure having a central axis, a front surface and a back surface that are generally perpendicular to the central axis, a central plane between and parallel to the front and back surfaces, a circumferential edge, and a radius extending from the central axis to the circumferential edge, wherein the structure further comprises:
a near-surface region extending substantially from the central axis to the circumferential edge and a distance, D 1 , of between about 0.5 μm and about 25 μm from the front surface toward the central plane,
a transition region extending substantially from the central axis to the circumferential edge and a distance, D 2 , of less than about 1 μm from the near-surface region toward the central plane,
a bulk region extending substantially from the central axis to the circumferential edge and a distance, D 3 , of greater than about 5 μm from the transition region toward the central plane,
wherein the bulk and near-surface regions are doped with a dopant, the concentration of dopant in the near-surface region is at least 10 times the maximum concentration, c, of dopant in the bulk region, and c is greater than about 5×10 13 atoms/cm 3 .
2. The silicon structure of claim 1 wherein D 1 is between about 0.5 μm and about 4 μm.
3. The silicon structure of claim 1 wherein D 1 is between about 6 μm and about 10 μm.
4. The silicon structure of claim 1 wherein D 1 is between about 10 μm and about 25 μm.
5. The silicon structure of claim 1 further comprising an epitaxial layer, wherein the epitaxial layer comprises the near-surface region and the transition region.
6. The silicon structure of claim 1 wherein the dopant in the bulk region and in the near-surface region is a p-type dopant.
7. The silicon structure of claim 6 wherein the p-type dopant is boron.
8. The silicon structure of claim 1 wherein the dopant in the bulk region and in the near-surface region is an n-type dopant.
9. The silicon structure of claim 8 wherein the n-type dopant is phosphorous.
10. The silicon structure of claim 1 wherein the dopant in the bulk region is a p-type dopant and the dopant in the near-surface region is an n-type dopant.
11. The silicon structure of claim 1 wherein the near-surface region is doped with a dopant in a concentration of at least about 100c.
12. The silicon structure of claim 1 wherein the near-surface region is doped with a dopant in a concentration of at least about 1000c.
13. The silicon structure of claim 1 wherein D 2 is about 0 μm.
14. The silicon structure of claim 1 wherein D 3 is at least about 10 μm.
15. The silicon structure of claim 1 wherein D 3 is at least about 20 μm.
16. The silicon structure of claim 1 wherein the bulk region extends from the transition region to the silicon structure's back surface.
17. The silicon structure of claim 1 wherein c is greater than about 1×10 14 atoms/cm 3 .
18. The silicon structure of claim 1 wherein c is greater than about 1×10 15 atoms/cm 3 .
19. The silicon structure of claim 1 wherein the structure further comprises recombination centers.
20. The silicon structure of claim 19 wherein the recombination centers are of a type selected from the group consisting of dislocation loops, oxygen precipitates, nitrogen precipitates, metastable metallic impurities, and combinations thereof.
21. The silicon structure of claim 19 wherein the silicon structure comprises at least about 1×10 11 per cm 3 recombination centers/cm 3 .
22. The silicon structure of claim 19 wherein the silicon structure comprises at least about 1×10 12 per cm 3 recombination centers/cm 3 .
23. A silicon structure having a central axis, a front surface and a back surface that are generally perpendicular to the central axis, a central plane between and parallel to the front and back surfaces, a circumferential edge, and a radius extending from the central axis to the circumferential edge, wherein the structure further comprises:
a near-surface region extending substantially from the central axis to the circumferential edge and a distance, D 1 , of between about 2.75 μm and about 3 μm from the front surface toward the central plane,
a transition region extending substantially from the central axis to the circumferential edge and a distance, D 2 , of less than about 1 μm from the near-surface region toward the central plane,
a bulk region extending substantially from the central axis to the circumferential edge and from the transition region to the back surface,
wherein the bulk region is doped with a dopant in a maximum dopant concentration of about 1×10 14 atoms/cm 3 and the near-surface region is doped with a dopant in a concentration of at least about 1×10 16 atoms/cm 3 .
24. A method for forming a silicon structure on a silicon substrate, the substrate having a central axis, a front surface and a back surface that are generally perpendicular to the central axis, a central plane between and parallel to the front and back surfaces, a circumferential edge, and a radius extending from the central axis to the circumferential edge, the method comprising:
forming a bulk region in the substrate, the bulk region being doped with a maximum dopant concentration of c wherein c is greater than about 5×10 13 atoms/cm 3 and extending substantially from the central axis to the circumferential edge and a distance, D 3 , from the front surface of the substrate toward the central plane of at least about 5 μm;
forming a transition region of doped silicon on the front surface of the substrate, the transition region extending substantially from the central axis to the circumferential edge and having a thickness, D 2 , of less than about 1 μm;
forming a near-surface region of doped silicon on the transition region, the near-surface region being doped with a dopant concentration of at least about 10 times c and extending substantially from the central axis to the circumferential edge and having a thickness, D 1 , of between about 0.5 μm and about 25 μm.
25. The method of claim 24 wherein the transition region and the near-surface region are formed by epitaxial deposition.
26. The method of claim 25 wherein the epitaxial deposition is carried out using a high concentration diborane source gas.
27. The method of claim 24 wherein the transition region and the near-surface region are formed by a direct bonding method.
28. The method of claim 24 wherein D 1 is between about 0.5 μm and about 4 μm.
29. The method of claim 24 wherein D 1 is between about 6 μm and about 10 μm.
30. The method of claim 24 wherein D 1 is between about 10 μm and about 25 μm.
31. The method of claim 24 wherein the dopant in the bulk region and in the near-surface region is a p-type dopant.
32. The method of claim 31 wherein the p-type dopant is boron.
33. The method of claim 24 wherein the dopant in the bulk region and in the near-surface region is an n-type dopant.
34. The method of claim 33 wherein the n-type dopant is phosphorous.
35. The method of claim 24 wherein the dopant in the bulk region is a p-type dopant and the near-surface region comprises an n-type dopant.
36. The method of claim 24 wherein the near-surface region is doped with a dopant in a concentration of at least about 100c.
37. The method of claim 24 wherein the near-surface region is doped with a dopant in a concentration of at least about 1000c.
38. The method of claim 24 wherein D 2 is about 0 μm.
39. The method of claim 24 wherein D 3 is at least about 10 μm.
40. The method of claim 24 wherein D 3 is at least about 20 μm.
41. The method of claim 24 wherein the bulk region extends from the transition region to the silicon structure's back surface.
42. The method of claim 24 wherein c is greater than about 1×10 14 atoms/cm 3 .
43. The method of claim 24 wherein c is greater than about 1×10 15 atoms/cm 3 .
44. The method of claim 24 further comprising the formation of recombination centers in the structure.
45. The method of claim 44 wherein the recombination centers are of a type selected from the group consisting of dislocation loops, oxygen precipitates, nitrogen precipitates, metastable metallic impurities, and combinations thereof.
46. The method of claim 44 wherein the silicon structure comprises at least about 1×10 11 per cm 3 recombination centers/cm 3 .
47. The method of claim 44 wherein the silicon structure comprises at least about 1×10 12 per cm 3 recombination centers/cm 3 .
48. The method of claim 44 wherein the recombination centers are formed before forming the transition region and the near-surface region.
49. The method of claim 44 wherein the recombination centers are formed during formation of the near-surface region.