Arsenic and phosphorus doped silicon wafer substrates having intrinsic gettering
View Patent ↗A process for the preparation of low resistivity arsensic or phosphorous doped (N+/N++) silicon wafers which, during the heat treatment cycles of essentially any arbitrary electronic device manufacturing process, reliably form oxygen precipitates.
1. A wafer sliced from a single crystal silicon ingot grown by the Czochralski method comprising:
a front surface, a back surface, an imaginary central plane between the front and back surfaces, a front surface layer which comprises a first region of a wafer between the front surface and a depth, D 1 , measured from the front surface and toward the central plane, and a bulk layer which comprises a second region of the wafer between the central plane and the first region; and
the wafer has a resistivity of less than 5 mΩ-cm, is doped with phosphorous or arsenic, and has a supersaturated concentration of crystal lattice vacancies in the bulk layer whereby (a) oxygen precipitates form in the bulk layer at a concentration of at least 1×10 7 oxygen precipitates/cm 3 upon subjecting the wafer to an oxygen precipitation heat-treatment at a temperature in excess of 700° C., and (b) the supersaturated concentration of crystal lattice vacancies is reduced and a formation of oxygen precipitates in the bulk layer at a concentration of at least 1×10 7 oxygen precipitates/cm 3 is avoided by (i) heating the wafer to an annealing temperature of at least 950° C. at a rate of at least 2° C./sec, and (ii) cooling the wafer from the annealing temperature to 700° C. or less before the wafer is subjected to an oxygen precipitation heat-treatment at a temperature in excess of 700° C.
2. The wafer of claim 1 wherein the bulk layer has an oxygen precipitate density of at least about 1×10 8 oxygen precipitates/cm 3 .
3. The wafer of claim 1 wherein the bulk layer has an oxygen precipitate density of at least about 1×10 9 oxygen precipitates/cm 3 .
4. The wafer of claim 1 wherein the front surface is polished.
5. The wafer of claim 1 wherein the front surface is lapped and etched.
6. The wafer of claim 1 further comprising an epitaxial layer on the front surface.
7. The wafer of claim 1 having a carbon concentration which is less than about 5×10 16 atoms/cm 3 .
8. The wafer of claim 1 having a carbon concentration which is less than about 1×10 16 atoms/cm 3 .
9. The wafer of claim 1 having a carbon concentration which is less than about 5×10 15 atoms/cm 3 .
10. The wafer of claim 1 wherein the dopant is arsenic.
11. The wafer of claim 10 wherein arsenic is present in a concentration of at least about 1×10 19 atoms/cm 3 .
12. The wafer of claim 10 wherein arsenic is present in a concentration from about 1×10 19 atoms/cm 3 to about 3×10 19 atoms/cm 3 .
13. The wafer of claim 10 wherein arsenic is present in a concentration from about 1.7×10 19 atoms/cm 3 to about 3×10 19 atoms/cm 3 .
14. The wafer of claim 10 wherein the resistivity of the wafer is from about 2.6 mΩ-cm to about 3.9 mΩ-cm.
15. The wafer of claim 1 wherein the dopant is phosphorous.
16. The wafer of claim 15 wherein phosphorous is present in a concentration of at least about 1×10 19 atoms/cm 3 .
17. The wafer of claim 15 wherein phosphorous is present in a concentration from about 1×10 19 atoms/cm 3 to about 4.5×10 19 atoms/cm 3 .
18. The wafer of claim 15 wherein phosphorous is present in a concentration from about 4.1×10 19 atoms/cm 3 to about 4.5×10 19 atoms/cm 3 .
19. The wafer of claim 15 wherein the resistivity of the wafer is from about 0.1 mΩ-cm and about 2 mΩ-cm.
20. The wafer of claim 15 wherein the resistivity of the wafer is from about 1.1 mΩ-cm and about 1.9 mΩ-cm.
21. The wafer of claim 1 wherein the supersaturated concentration of crystal lattice vacancies in the bulk layer is 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.
22. The wafer of claim 1 wherein the supersaturated concentration of crystal lattice vacancies in the bulk layer is a non-uniform concentration of crystal lattice vacancies in which a peak concentration is at or near the front surface layer, the concentration generally decreasing in the direction of the central plane.
23. The wafer of claim 1 wherein the first region of the wafer between the front surface and a depth, D 1 , measured from the front surface and toward the central plane comprises oxygen precipitates at a concentration of less than 1×10 7 oxygen precipitates/cm 3 upon subjecting the wafer to an oxygen precipitation heat-treatment at a temperature in excess of 700° C.
24. The wafer of claim 23 wherein D 1 is greater than 10 μm.
25. The wafer of claim 23 wherein D 1 is less than 10 μm.
26. The wafer of claim 23 wherein D 1 is less than 2 μm.