Claims
- 1. A wafer sliced from a single crystal silicon ingot grown in accordance with the Czochralski method, the wafer comprising:
a front surface, a back surface, an imaginary central plane approximately equidistant between the front and back surfaces, a front surface layer which comprises a region of the wafer between the front surface and a distance, D1, measured from the front surface and toward the central plane, and a bulk layer which comprises the imaginary central plane but not the front surface layer, and a non-uniform concentration of crystal lattice vacancies in which a peak concentration is in the bulk layer between the central plane and the front surface layer, the concentration generally decreasing in the direction of both the front surface layer and the central plane, wherein (i) D1 is at least about 5 microns but less than about 30 microns, and (ii) upon being subjected to an oxygen precipitation heat-treatment at a temperature in excess of about 700° C., the surface layer has less than about 1×107 cm−3 oxygen precipitates while the bulk layer has more than about 1×107 cm−3 oxygen precipitates.
- 2. The wafer of claim 1 wherein the bulk has an oxygen precipitate density of greater than about 1×108 cm−3.
- 3. The wafer of claim 1 wherein the bulk has an oxygen precipitate density of greater than about 1×109 cm−3.
- 4. The wafer of claim 1 wherein the bulk has an oxygen precipitate density of greater than about 1×1010 cm−3.
- 5. The wafer of claim 1 further comprising an epitaxial layer on the front surface.
- 6. The wafer of claim 1 having a carbon concentration which is less than about 5×1016 atoms/cm3.
- 7. The wafer of claim 1 having a carbon concentration which is less than about 1×1016 atoms/cm3.
- 8. The wafer of claim 1 having a carbon concentration which is less than about 5×1015 atoms/cm3.
- 9. The wafer of claim 1 wherein the front surface is polished.
- 10. The wafer of claim 1 wherein the wafer has an absence of oxygen precipitate nucleation centers which are incapable of being dissolved by heat-treating the wafer at a temperature not in excess of about 1300° C.
- 11. The wafer of claim 1 wherein the resistivity thereof is less than about 50 ohm cm.
- 12. The wafer of claim 1 wherein D1 is greater than about 10 microns and less than about 25 microns.
- 13. The wafer of claim 12 wherein the bulk has an oxygen precipitate density of greater than about 1×108 cm−3.
- 14. The wafer of claim 12 wherein the bulk has an oxygen precipitate density of greater than about 1×1010 cm−3.
- 15. The wafer of claim 12 further comprising an epitaxial layer on the front surface.
- 16. The wafer of claim 12 having a carbon concentration which is less than about 5×1016 atoms/cm3.
- 17. The wafer of claim 12 having a carbon concentration which is less than about 5×1015 atoms/cm3.
- 18. The wafer of claim 12 wherein the front surface is polished.
- 19. The wafer of claim 12 wherein the wafer has an absence of oxygen precipitate nucleation centers which are incapable of being dissolved by heat-treating the wafer at a temperature not in excess of about 1300° C.
- 20. The wafer of claim 12 wherein the resistivity thereof is less than about 50 ohm cm.
- 21. The wafer of claim 1 wherein D1 ranges from greater than about 15 microns to less than about 20 microns.
- 22. The wafer of claim 21 wherein the bulk has an oxygen precipitate density of greater than about 1×108 cm−3.
- 23. The wafer of claim 21 wherein the bulk has an oxygen precipitate density of greater than about 1×1010 cm−3.
- 24. The wafer of claim 21 further comprising an epitaxial layer on the front surface.
- 25. The wafer of claim 21 having a carbon concentration which is less than about 5×1016 atoms/cm3.
- 26. The wafer of claim 21 having a carbon concentration which is less than about 5×1015 atoms/cm3.
- 27. The wafer of claim 21 wherein the front surface is polished.
- 28. The wafer of claim 21 wherein the wafer has an absence of oxygen precipitate nucleation centers which are incapable of being dissolved by heat-treating the wafer at a temperature not in excess of about 1300° C.
- 29. The wafer of claim 21 wherein the resistivity thereof is less than about 50 ohm cm.
- 30. A process for preparing a silicon wafer, the wafer being sliced from a single crystal silicon ingot grown in accordance with the Czochralski method and having a front surface, a back surface, an imaginary central plane approximately equidistant between the front and back surfaces, a front surface layer which comprises a region of the wafer between the front surface and a distance, D1, which as measured from the front surface and toward the central plane is greater than about 5 microns but less than about 30 microns, and a bulk layer which comprises the imaginary central plane but not the front surface layer, the process comprising:
heat-treating the single crystal silicon wafer in an atmosphere comprising a nitrogen-containing gas and an oxygen-containing gas, the concentration of oxygen in the atmosphere being less than about 500 PPMA, to form crystal lattice vacancies in the front surface layer and in the bulk layer; cooling the heat-treated wafer to produce therein a non-uniform concentration of crystal lattice vacancies in which a peak concentration is in the bulk layer between the central plane and the front surface layer, the concentration generally decreasing in the direction of both the front surface layer and the central plane, and subjecting the cooled wafer to an oxygen precipitation heat-treatment at a temperature in excess of about 700° C. to form a wafer having a denuded zone in the front surface layer and oxygen precipitates in the bulk layer.
- 31. The process of claim 30 wherein the bulk layer has an oxygen precipitate density of greater than about 1×107 cm−3.
- 32. The process of claim 30 wherein the bulk layer has an oxygen precipitate density of greater than about 1×108 cm−3.
- 33. The process of claim 30 wherein the bulk layer has an oxygen precipitate density of greater than about 1×109 cm−3.
- 34. The process of claim 30 wherein the bulk layer has an oxygen precipitate density of greater than about 1×1010 cm−3.
- 35. The process of claim 30 wherein the nitrogen-containing gas is a nitrogen-containing compound gas.
- 36. The process of claim 35 wherein the nitrogen-containing compound gas is ammonia.
- 37. The process of claim 35 wherein the nitrogen-containing gas is elemental nitrogen.
- 38. The process of claim 35 wherein the oxygen-containing gas is elemental oxygen or pyrogenic steam.
- 39. The process of claim 30 wherein the wafer is heat treated in an atmosphere further comprising an inert gas.
- 40. The process of claim 39 wherein the inert gas is selected from argon, helium, neon, carbon dioxide or a mixture thereof.
- 41. The process of claim 40 wherein the atmosphere comprises nitrogen, argon and oxygen.
- 42. The process of claim 39 wherein the ratio of nitrogen-containing gas to inert gas ranges from about 1:10 to about 10:1.
- 43. The process of claim 39 wherein the ratio of nitrogen-containing gas to inert gas ranges from about 1:5 to about 5:1.
- 44. The process of claim 39 wherein the ratio of nitrogen-containing gas to inert gas ranges from about 1:4 to about 4:1.
- 45. The process of claim 39 wherein the ratio of nitrogen-containing gas to inert gas ranges from about 1:3 to about 3:1.
- 46. The process of claim 39 wherein the ratio of nitrogen-containing gas to inert gas ranges from about 1:2 to about 2:1.
- 47. The process of claim 30 wherein the concentration of nitrogen-containing gas in the atmosphere ranges from about 1% to less than about 100% .
- 48. The process of claim 30 wherein the concentration of nitrogen-containing gas in the atmosphere ranges from about 10% to about 90%.
- 49. The process of claim 30 wherein the concentration of nitrogen-containing gas in the atmosphere ranges from about 20% to about 80%.
- 50. The process of claim 30 wherein the concentration of nitrogen-containing gas in the atmosphere ranges from about 40% to about 60%.
- 51. The process of claim 30 wherein the atmosphere has an oxygen partial pressure of less than about 400 PPMA.
- 52. The process of claim 30 wherein the atmosphere has an oxygen partial pressure of less than about 200 PPMA.
- 53. The process of claim 30 wherein the atmosphere has an oxygen partial pressure of less than about 100 PPMA.
- 54. The process of claim 30 wherein the atmosphere has an oxygen partial pressure of less than about 50 PPMA.
- 55. The process of claim 30 wherein the atmosphere has an oxygen partial pressure of less than about 10 PPMA.
- 56. The process of claim 30 wherein D1 is greater than about 10 microns and less than about 25 microns.
- 57. The process of claim 30 wherein D1 is greater than about 15 microns and less than about 20 microns.
- 58. The process of claim 30 wherein the atmosphere has an oxygen partial pressure of less than about 300 PPMA but greater than about 5 PPMA.
- 59. The process of claim 30 wherein the atmosphere has an oxygen partial pressure of less than about 200 PPMA but greater than about 10 PPMA.
- 60. The process of claim 30 wherein the atmosphere has an oxygen partial pressure of less than about 100 PPMA but greater than about 20 PPMA.
- 61. The process of claim 30 wherein the atmosphere consists essentially of a combination of a nitrogen-containing gas and an oxygen-containing gas.
- 62. The process of claim 30 wherein the atmosphere consists essentially of a combination of a nitrogen-containing gas, an oxygen-containing gas and an inert gas.
- 63. The process of claim 30 wherein the heat-treated wafer is cooled at a rate of at least about 20° C./second through the temperature range in which crystal lattice vacancies are relatively mobile in silicon.
- 64. The process of claim 30 wherein the heat-treated wafer is cooled at a rate of at least about 50° C./second through the temperature range in which crystal lattice vacancies are relatively mobile in silicon.
- 65. The process of claim 30 wherein the heat-treated wafer is cooled at a rate of at least about 100° C./second through the temperature range in which crystal lattice vacancies are relatively mobile in silicon.
- 66. The process of claim 30 wherein the wafer is heated-treated to form crystal lattice vacancies at a temperature of at least about 1150° C. for a period of less than about 60 seconds.
- 67. The process of claim 30 wherein the wafer is heated-treated to form crystal lattice vacancies at a temperature of at least about 1175° C. for a period of less than about 60 seconds.
- 68. The process of claim 30 wherein the surface layer has a resistivity of less than about 50 ohm cm.
- 69. The process of claim 30 wherein the bulk layer has a resistivity of less than about 50 ohm cm.
REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional Application Serial No. 60/371,324 which was filed Apr. 10, 2002. The entire contents of this application are incorporated herein by reference.
Provisional Applications (1)
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Number |
Date |
Country |
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60371324 |
Apr 2002 |
US |