Process for producing silicon carbide crystals having increased minority carrier lifetimes

• US 20060130742A1
• Filed: 02/07/2005
• Published: 06/22/2006
• Est. Priority Date: 12/22/2004
• Status: Active Grant

• Current Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Original Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Inventors: Tsvetkov, Valeri F., Hobgood, Hudson M., Carter, Calvin H. Jr., Das, Mrinal K., Jenny, Jason R., Malta, David P.
• Granted Patent: US 7,811,943 B2
• Time in Patent Office: Days
• US Class Current: 117/84
• CPC Class Codes: C30B 11/003 Heating or cooling of the melt or the crystallised material
• CPC Class Codes: C30B 29/36 Carbides
• CPC Class Codes: C30B 33/02 Heat treatment C30B33/04, C30B33/06 take precedence

Abstract

A process is described for producing silicon carbide crystals having increased minority carrier lifetimes. The process includes the steps of heating and slowly cooling a silicon carbide crystal having a first concentration of minority carrier recombination centers such that the resultant concentration of minority carrier recombination centers is lower than the first concentration.

Claims

1. A process for producing silicon carbide crystals having increased minority carrier lifetimes, comprising:

heating a silicon carbide crystal having a first concentration of minority carrier recombination centers resulting in a first minority carrier lifetime and thereafter cooling the heated silicon carbide crystal at a rate sufficiently slow to provide a silicon carbide crystal having a second concentration of minority carrier recombination centers that is lower than the first concentration thereby providing a material having an increased minority carrier lifetime.

2. The process of claim 1, wherein the heating step comprises heating the silicon carbide crystal to a temperature greater than its growth temperature.

3. The process of claim 2, wherein the heating step comprises heating the silicon carbide crystal to a temperature of at least about 2400°

C. and maintaining said heated silicon carbide crystal at a temperature of at least about 2400°

C. for up to about one hour in an inert ambient atmosphere.

4. The process of claim 3, wherein the heating step comprises heating the silicon carbide crystal to a temperature ranging from about 2400°

C. to about 2700°

C. and maintaining said heated silicon carbide crystal at a temperature ranging from about 2400°

C. to about 2700°

C. for up to about one hour in an inert ambient atmosphere.

5. The process of claim 4, wherein the heating step comprises heating the silicon carbide crystal to a temperature of about 2600°

C. and maintaining said heated silicon carbide crystal at a temperature of about 2600°

C. for up to about one hour in an inert ambient atmosphere.

6. The process of claim 3, wherein the cooling step comprises cooling the heated silicon carbide crystal at a rate of about 2°

C. per minute or less to a temperature of about 1400°

C. to about 1000°

C.

7. The process of claim 6, wherein the cooling step comprises cooling the heated silicon carbide crystal at a rate of about 2°

C. per minute or less to a temperature of about 1200°

C.

8. The process of claim 6, wherein the cooling step further comprises cooling the silicon carbide crystal from about 1200°

C. to about room temperature at a rate from about 2°

C. per minute to about 10°

C. per minute.

9. The process of claim 1, wherein the heating step comprises heating a bulk silicon carbide single crystal.

10. The process of claim 1, wherein the heating step comprises heating an epitaxial silicon carbide layer or layers.

11. The process of claim 1, wherein the heating step comprises heating a silicon carbide crystal comprising dopant in an amount of about 1×

10¹⁷ cm<sup>−

3</sup> or less.

12. The process of claim 1, wherein the heating and cooling steps comprise heating and cooling a silicon carbide crystal having a first minority carrier lifetime under conditions sufficient to increase the minority carrier lifetime of the thus heated and cooled crystal and thereby provide a material more suitable for use as a high voltage blocking device as compared to the crystal prior to said heating and cooling steps.

13. The process of claim 12, wherein the heating and cooling steps comprise heating and cooling a silicon carbide crystal under conditions sufficient to provide a silicon carbide crystal exhibiting a minority carrier lifetime of at least about 1 microseconds (μ

s) or greater.

14. The process of claim 13, wherein the heating and cooling steps comprise heating and cooling a silicon carbide crystal under conditions sufficient to provide a silicon carbide crystal exhibiting a minority carrier lifetime of at least about 4 microseconds (μ

s) or greater.

15. The process of claim 14, comprising heating and cooling a silicon carbide crystal under conditions sufficient to provide a silicon carbide crystal exhibiting a minority carrier lifetime of at least about 30 microseconds (μ

s) or greater.

16. A silicon carbide crystal made by the process of claim 1.

20. A semiconductor device comprising a silicon carbide crystal made by the process of claim 1.

21. The device of claim 20, wherein said device is a power device.

22. The device of claim 20, wherein said device is selected from the group consisting of pn diodes, PiN diodes, thyristors, and IGBTs.

17. A bulk silicon carbide single crystal having a minority carrier lifetime of at least about 1 microseconds.

18. The bulk silicon carbide single crystal of claim 17, wherein said crystal has a minority carrier lifetime of at least about 4 microseconds.

19. The silicon carbide single crystal of claim 18, wherein said crystal has a minority carrier lifetime of at least about 30 microseconds.

23. A semiconductor device comprising a silicon carbide single crystal having a minority carrier lifetime of at least about 1 microseconds.

24. The device of claim 23, wherein said crystal has a minority carrier lifetime of at least about 4 microseconds.

25. The device of claim 24, wherein said crystal has a minority carrier lifetime of at least about 30 microseconds.

26. A process for the production of a device comprising a silicon carbide crystal exhibiting increased minority carrier lifetime, comprising:

heating a silicon carbide crystal having a first concentration of minority carrier recombination centers resulting in a first minority carrier lifetime and thereafter cooling the heated silicon carbide crystal at a rate sufficiently slow to provide a silicon carbide crystal having a second concentration of minority carrier recombination centers that is lower than the first concentration thereby providing a material having an increased minority carrier lifetime; and

incorporating said silicon carbide crystal into a device.

27. The process of claim 26, wherein the incorporating step comprises incorporating said silicon carbide crystal into a device after said heating and cooling steps.

28. The process of claim 26, wherein the incorporating step comprises incorporating said silicon carbide crystal into a power device.

29. The process of claim 28, wherein the incorporating step comprises incorporating said silicon carbide crystal into a p-n diode.

30. The process of claim 28, wherein the incorporating step comprises incorporating said silicon carbide crystal into a PiN diode.

31. The process of claim 30, wherein the heating and cooling steps comprise heating and cooling a silicon carbide crystal having a first minority carrier lifetime under conditions sufficient to increase the minority carrier lifetime of said crystal to a level sufficient to increase the conductivity modulation of the thus heated and cooled crystal and thereby provide a material more suitable for use as a high voltage blocking device as compared to the crystal prior to said heating and cooling steps.