Process for preparing a stabilized ideal oxygen precipitating silicon wafer
View Patent ↗The present invention is directed to a single crystal Czochralski-type silicon wafer, and a process for the preparation thereof, which has a non-uniform distribution of stabilized oxygen precipitate nucleation centers therein. Specifically, the peak concentration is located in the wafer bulk and a precipitate-free zone extends inward from a surface.
1. A process for the preparation of a single crystal silicon wafer having a controlled oxygen precipitation behavior, the process comprising the steps of:
selecting a wafer sliced from a single crystal silicon ingot grown by the Czochralski method comprising a front surface, a back surface, a central plane between the front and back surfaces, a front surface layer which comprises the region of the wafer between the front surface and a distance D measured from the front surface and toward the central plane, and a bulk layer which comprises the region of the wafer between the central plane and the front surface layer;
heating the wafer to an annealing temperature T A to form crystal lattice vacancies in the front surface and bulk layers;
cooling the heated wafer from T A to an upper nucleation temperature T U at a rate R to form a vacancy concentration profile in the wafer wherein the peak density of vacancies is in the bulk layer with the concentration generally decreasing from the location of the peak density in the direction of the front surface of the wafer; and
controlling cooling of the vacancy concentration profiled wafer from an upper nucleation temperature T U to a lower nucleation temperature T L for a nucleation duration t n to form oxygen precipitate nucleation centers in the bulk layer that are incapable of being dissolved at temperatures below about 1150° C. and a region free of oxygen precipitate nucleation centers in the surface layer.
2. The process of claim 1 wherein T A is in excess of about 1150° C.
3. The process of claim 1 wherein T A is between about 1200 and about 1400° C.
4. The process of claim 1 wherein T A is between about 1250 and about 1400° C.
5. The process of claim 1 wherein T A is between about 1300 and about 1400° C.
6. The process of claim 1 wherein T A is between about 1350 and about 1400° C.
7. The process of claim 1 wherein R is at least about 5° C. per second.
8. The process of claim 1 wherein R is at least about 20° C. per second.
9. The process of claim 1 wherein R is at least about 50° C. per second.
10. The process of claim 1 wherein R is at least about 100° C. per second.
11. The process of claim 1 wherein R is between about 100 and about 200° C. per second.
12. The process of claim 1 wherein R is between about 30 and about 80° C. per second.
13. The process of claim 1 wherein R is between about 40 and about 50° C. per second.
14. The process of claim 1 wherein T U is between about 920 and about 1090° C., T L is between about 890 and about 1080° C., the difference between T U and T L is less than about 40° C. and generally decreases as T U and T L increase, and t n is between about 10 and about 360 seconds.
15. The process of claim 1 wherein T U is between about 970 and about 1090° C., T L is between about 950 and about 1080° C., the difference between T U and T L is less than about 25° C. and generally decreases as T U and T L increase, and t n is between about 10 and about 90 seconds.
16. The process of claim 1 wherein T U is between about 1020 and about 1090° C., T L is between about 1000 and about 1080° C., the difference between T U and T L is less than about 20° C. and generally decreases as T U and T L increase, and t n is between about 10 and about 30 seconds.
17. The process of claim 1 wherein T U is between about 1060 and about 1090° C., T L is between about 1050 and about 1080° C., and the difference between T U and T L is less than about 15° C. and generally decreases as T U and T L increase, and t n is between about 10 and about 15 seconds.
18. The process of claim 1 wherein, prior to the heat-treatment to form crystal lattice vacancies, the wafer is heated to a temperature of at least about 700° C. in an oxygen-containing atmosphere to form a superficial silicon dioxide layer which is capable of serving as a sink for crystal lattice vacancies.
19. The process of claim 1 comprising depositing an epitaxial layer on at least one surface of the wafer after formation of the stabilized oxygen precipitate nucleation centers form in the bulk layer.
20. A process for the preparation of a single crystal silicon wafer having a controlled oxygen precipitation behavior, the process comprising the steps of:
selecting a wafer sliced from a single crystal silicon ingot grown by the Czochralski method comprising a front surface, a back surface, a central plane between the front and back surfaces, a front surface layer which comprises the region of the wafer between the front surface and a distance D measured from the front surface and toward the central plane, and a bulk layer which comprises the region of the wafer. between the central plane and the front surface layer;
heating the wafer to an annealing temperature T A that is at least about 1300° C. to form crystal lattice vacancies in the front surface and bulk layers;
cooling the heated wafer from T A to an upper nucleation temperature T U that is between about 1020 and about 1090° C. at a rate R that is between about 40 and 50° C./sec to form a vacancy concentration profile in the wafer wherein the peak density of vacancies is in the bulk layer with the concentration generally decreasing from the location of the peak density in the direction of the front surface of the wafer; and
controlling cooling of the vacancy concentration profiled wafer from an upper nucleation temperature T U to a lower nucleation temperature T L that is between about 1000 and about 1080° C. wherein the difference between T U and T L is no greater than about 20° C. and generally decreases as T U and T L increase for a nucleation duration t n that is between about 10 and about 30 seconds to form oxygen precipitate nucleation centers in the bulk layer that are incapable of being dissolved at temperatures below about 1150° C. and a region free of oxygen precipitate nucleation centers in the surface layer.
21. A process for the preparation of a single crystal silicon wafer having a controlled oxygen precipitation behavior, the process comprising the steps of:
selecting a wafer sliced from a single crystal silicon ingot grown by the Czochralski method comprising a front surface, a back surface, a central plane between the front and back surfaces, a front surface layer which comprises the region of the wafer between the front surface and a distance D measured from the front surface and toward the central plane, and a bulk layer which comprises the region of the wafer between the central plane and the front surface layer;
heating the wafer to an annealing temperature T A that is at least about 1350° C. to form crystal lattice vacancies in the front surface and bulk layers;
cooling the heated wafer from T A to an upper nucleation temperature T U that is between about 1060 and about 1090° C. at a rate R that is between about 40 and 50° C./sec to form a vacancy concentration profile in the wafer wherein the peak density of vacancies is in the bulk layer with the concentration generally decreasing from the location of the peak density in the direction of the front surface of the wafer; and
controlling cooling of the vacancy concentration profiled wafer from an upper nucleation temperature T U to a lower nucleation temperature T L that is between about 1050 and about 1080° C. wherein the difference between T U and T L is no greater than about 15° C. and generally decreases as T U and T L increase for a nucleation duration t n that is between about 10 and about 15 seconds to form oxygen precipitate nucleation centers in the bulk layer that are incapable of being dissolved at temperatures below about 1150° C. and a region free of oxygen precipitate nucleation centers in the surface layer.
22. A process for the preparation of a single crystal silicon wafer having a controlled oxygen precipitation behavior, the process comprising the steps of:
selecting a wafer sliced from a single crystal silicon ingot grown by the Czochralski method comprising a front surface, a back surface, a central plane between the front and back surfaces, a front surface layer which comprises the region of the wafer between the front surface and a distance D measured from the front surface and toward the central plane, a bulk layer which comprises the region of the wafer between the central plane and the front surface layer and a native oxide layer on the front and back surfaces;
heating the wafer to an annealing temperature T A to form crystal lattice vacancies in the front surface and bulk layers while exposing the wafer to an atmosphere comprising nitrogen or a nitrogen-containing gas;
cooling the heated wafer from T A to an upper nucleation temperature T U at a rate R to form a vacancy concentration profile in the wafer wherein the peak density of vacancies is in the bulk layer with the concentration generally decreasing from the location of the peak density in the direction of the front surface of the wafer; and
controlling cooling of the vacancy concentration profiled wafer from an upper nucleation temperature T U to a lower nucleation temperature T L for a nucleation duration t n to form oxygen precipitate nucleation centers in the bulk layer that are incapable of being dissolved at temperatures below about 1150° C. and a region free of oxygen precipitate nucleation centers in the surface layer.