Method for controlling of thermal donor formation in high resistivity CZ silicon
View Patent ↗The present invention is directed to a single crystal Czochralski-type silicon wafer, and a process for the preparation thereof, which has at least a surface layer of high resistivity, the layer having an interstitial oxygen content which renders it incapable of forming thermal donors in an amount sufficient to affect resistivity upon being subjected to a conventional semiconductor device manufacturing process. The present invention further directed to a silicon on insulator structure derived from such a wafer.
1. 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 has a resistivity of greater than about 50 ohm cm and which comprises a region of the wafer between the front surface and a distance, D 1 , 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 a rapid thermal annealer to form crystal lattice vacancies in the front surface layer and in the bulk layer; and
rapidly cooling the heat-treated wafer to form a template for oxygen precipitation.
2. The process of claim 1 wherein upon being subjected to an oxygen precipitation heat-treatment at a temperature in excess of about 700° C., oxygen precipitates form in the bulk layer and in the front surface layer.
3. The process of claim 1 wherein upon being subjected to an oxygen precipitation heat-treatment at a temperature in excess of about 700° C., oxygen precipitates form in the bulk layer but not in the front surface layer.
4. The process of claim 1 wherein the process additionally comprises subjecting the 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 wherein the bulk layer has an oxygen precipitate density of greater than about 1×10 7 cm −3 .
5. The process of claim 1 wherein the process additionally comprises subjecting the 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 wherein the bulk layer has an oxygen precipitate density of greater than about 1×10 8 cm −3 .
6. The process of claim 1 wherein prior to the oxygen precipitation heat treatment, the wafer had an interstitial oxygen concentration of less than about 10 ppma.
7. The process of claim 1 wherein the silicon wafer is heat-treated, and the heat-treated wafer cooled, in an atmosphere comprising a mixture of an oxygen-containing gas and a nitrogen-containing gas.
8. The process of claim 7 wherein the atmosphere comprises a nitrogen-containing compound gas.
9. The process of claim 8 wherein the nitrogen-containing compound gas is ammonia.
10. The process of claim 7 wherein the nitrogen-containing gas is elemental nitrogen.
11. The process of claim 7 wherein the oxygen-containing gas is elemental oxygen or pyrogenic steam.
12. The process of claim 7 wherein the gaseous mixture further comprises an inert gas.
13. The process of claim 12 wherein the inert gas is selected from argon, helium, neon, carbon dioxide or a mixture thereof.
14. The process of claim 7 wherein the atmosphere comprises nitrogen, argon and oxygen.
15. The process of claim 14 wherein the ratio of nitrogen-containing gas to inert gas ranges from about 1:5 to about 5:1.
16. The process of claim 14 wherein the ratio of nitrogen-containing gas to inert gas ranges from about 1:4 to about 4:1.
17. The process of claim 14 wherein the ratio of nitrogen-containing gas to inert gas is about 1:5.
18. The process of claim 14 wherein the ratio of nitrogen-containing gas to inert gas is about 1:3.
19. The process of claim 7 wherein the concentration of nitrogen-containing gas in the gaseous mixture ranges from about 10% to about 90%.
20. The process of claim 7 wherein the concentration of nitrogen-containing gas in the gaseous mixture ranges from about 20% to about 80%.
21. The process of claim 7 wherein the atmosphere has an oxygen partial pressure of less than about 400 ppma.
22. The process of claim 7 wherein the atmosphere has an oxygen partial pressure of less than about 200 ppma.
23. The process of claim 1 wherein the heat-treated wafer is cooled at a rate of at least about 20° C./second through the temperature range at which crystal lattice vacancies are relatively mobile in silicon.
24. The process of claim 1 wherein the heat-treated wafer is cooled at a rate of at least about 50° C./second through the temperature range at which crystal lattice vacancies are relatively mobile in silicon.
25. The process of claim 1 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.
26. The process of claim 1 wherein the process additionally comprises the step of bonding the wafer to another wafer to form a bonded composite.
27. The process of claim 1 wherein the process additionally comprises the step of implanting ions into the wafer.
28. The process of claim 1 wherein the process additionally comprises the step of depositing an epitaxial layer onto the surface of the wafer.
29. The process of claim 1 wherein the front surface layer of the wafer has a resistivity of greater than about 100 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, the wafer having an interstitial oxygen concentration of less than about 10 ppma, a front surface, a back surface, an imaginary central plane approximately equidistant between the front and back surfaces, a front surface layer which has a resistivity of greater than about 50 ohm cm and which comprises a region of the wafer between the front surface and a distance, D 1 , 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 to form crystal lattice vacancies in the front surface layer and in the bulk layer; and,
cooling the heat-treated wafer to produce a non-uniform vacancy concentration profile in which the peak vacancy concentration is in the bulk layer.
31. The process of claim 30 wherein the oxygen concentration of the wafer is less than about 9 ppma.
32. The process of claim 30 wherein D 1 is greater than about 5 microns and less than about 20 microns.
33. The process of claim 30 wherein the surface layer has a resistivity of greater than about 100 ohm cm.
34. The process of claim 30 wherein the surface layer has a resistivity of greater than about 200 ohm cm.
35. 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 at which crystal lattice vacancies are relatively mobile in silicon.
36. 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.