Recrystallization method to selenization of thin-film Cu(In,Ga)Se.sub.2 for semiconductor device applications

• US 5,436,204 A
• Filed: 08/22/1994
• Issued: 07/25/1995
• Est. Priority Date: 04/12/1993
• Status: Expired due to Term

• Current Assignee: Alliance For Sustainable Energy LLC
• Original Assignee: Midwest Research Institute
• Inventors: Gabor, Andrew M., Carapella, Jeffrey J., Albin, David S., Tuttle, John R., Noufi, Rommel, Contreras, Miguel A., Tennant, Andrew L.
• Primary Examiner(s): Thomas, Tom
• Assistant Examiner(s): NGUYEN, TUAN H
• Application Number:
  US08/293,826
• Time in Patent Office: 337 Days
• Field of Search: 437/225, 437/5, 437/247, 437/103, 437/106, 437/234, 136/260, 136/265, 136/258, 136/264
• US Class Current: 438/488
• CPC Class Codes: H01L 31/0322 comprising only AIBIIICVI chalcopyrite compounds, e.g. Cu In Se2, Cu Ga Se2, Cu In Ga Se2
• CPC Class Codes: Y02E 10/541 CuInSe2 material PV cells
• CPC Class Codes: Y02P 70/50 Manufacturing or production processes characterised by the final manufactured product

Abstract

A process for fabricating slightly Cu-poor thin-films of Cu(In,Ga)Se₂ on a substrate for semiconductor device applications includes the steps of forming initially a slightly Cu-rich, phase separated, mixture of Cu(In,Ga)Se₂ :Cu_x Se on the substrate in solid form followed by exposure of the Cu(In,Ga)Se₂ :Cu_x Se solid mixture to an overpressure of Se vapor and (In,Ga) vapor for deposition on the Cu(In,Ga)Se₂ :Cu_x Se solid mixture while simultaneously increasing the temperature of the solid mixture toward a recrystallization temperature (about 550° C.) at which Cu(In,Ga)Se₂ is solid and Cu_x Se is liquid. The (In,Ga) flux is terminated while the Se overpressure flux and the recrystallization temperature are maintained to recrystallize the Cu_x Se with the (In, Ga) that was deposited during the temperature transition and with the Se vapor to form the thin-film of slightly Cu-poor Cu_x (In,Ga)_y Se_z. The initial Cu-rich, phase separated large grain mixture of Cu(In,Ga)Se₂ :Cu_x Se can be made by sequentially depositing or co-depositing the metal precursors, Cu and (In, Ga), on the substrate at room temperature, ramping up the thin-film temperature in the presence of Se overpressure to a moderate anneal temperature (about 450° C.) and holding that temperature and the Se overpressure for an annealing period. A nonselenizing, low temperature anneal at about 100° C. can also be used to homogenize the precursors on the substrates before the selenizing, moderate temperature anneal.

Claims

1. A process for fabricating thin-film semiconductor devices, comprising the steps of:

depositing thin-film precursors of Cu and (In,Ga) on a substrate in a Cu-rich ratio with Cu/(In,Ga)>

1.0;

annealing the thin-film precursors in the presence of Se at a moderate temperature in the range of 400°

-500°

C. to form thin-film Cu(In,Ga)Se₂ ;

Cu_x Se phase-separated mixture;

exposing the thin-film Cu(In,Ga)Se₂ ;

Cu_x Se phase-separated mixture to (In,Ga) vapor in addition to Se to deposit (In,Ga) and Se on the thin-film Cu(In,Ga)Se₂ ;

Cu_x Se phase-separated mixture while raising the temperature of the thin-film Cu(In,Ga)Se₂ ;

Cu_x Se phase-separated mixture from the moderate temperature to a higher recrystallization temperature to a higher recrystallization temperature in the range of 500°

-600°

C.;

maintaining the thin-film at the higher recrystallization temperature to recrystallize the Cu_x Se with the (In,Ga) and Se to form a Cu(In,Ga)Se₂ thin-film in a Cu-poor ratio of Cu/(In,Ga)<

1.0.

2. The process of claim 1, including the step of maintaining the presence of Se while cooling the Cu(In,Ga)Se₂ thin-film to a temperature below the higher recrystallization temperature.

3. The process of claim 2, wherein said cooling occurs at a rate of about 12.5°

C./minute.

4. The process of claim 2, wherein the temperature below the higher recrystallization temperature is in the range of 250°

-350°

C.

5. The process of claim 4, including the step of removing the Se presence when the temperature of the Cu(In,Ga)Se₂ thin-film drops to said temperature below the higher recrystallization temperature.

6. The process of claim 4, wherein said temperature below the higher recrystallization temperature is about 300°

C.

7. The process of claim 1, wherein said moderate temperature is about 450°

C.

8. The process of claim 1, wherein said higher recrystallization temperature is about 550°

C.

9. The process of claim 1, including the step of providing said Se in a vapor overpressure.

10. The process of claim 1, wherein the step of providing said Se in a vapor overpressure is at a flux rate of about 20 Å

/second.

11. The method of claim 1, wherein said step of exposing the thin-film Cu(In,Ga)Se₂ :

Cu_x Se phase-separated mixture to (In,Ga) vapor includes In with no Ga.

12. The method of claim 1, wherein said step of exposing the thin-film Cu(In,Ga)Se₂ :

Cu_x Se phase-separated mixture to (In,Ga) vapor includes providing the (In,Ga) in a vapor at a flux ram of about 4 Å

/second.

13. The method of claim 1, wherein said step of exposing the thin-film Cu(In,Ga)Se₂ :

Cu_x Se phase-separated mixture to (In,Ga) includes raising the temperature of the thin-film Cu(In,Ga)Se₂ ;

Cu_x Se phase-separated mixture from the moderate temperature to the higher recrystallization temperature over a period of time and exposing the thin-film Cu(In,Ga)Se₂ ;

Cu_x Se phase-separated mixture to the (In,Ga) for a portion less than said period of time.

14. The method of claim 13, wherein said period of time is in the range of three to nine minutes.

15. The method of claim 13, wherein said period of time is about six minutes.

16. The method of claim 15, wherein said step of exposing said thin-film Cu(In,Ga)Se₂ :

Cu_x Se phase-separated mixture to (In,Ga) occurs during the first two minutes of said six-minute time period.

17. The method of claim 1, wherein said step of maintaining the thin-film at the higher recrystallization temperature extends for a time period in the range of five to fifteen minutes.

18. The method of claim 1, wherein said step of maintaining the thin-film at the higher recrystallization temperature extends for a time period of about ten minutes.

19. The method of claim 1, wherein said step of annealing the thin-film precursors in the presence of Se occurs over a time period in the range of about ten to thirty minutes.

20. The method of claim 1, wherein said step of annealing the thin-film precursors in the presence of Se occurs over a time period of about twenty minutes.

21. The method of claim 1, including the step of depositing the thin-film precursors of Cu and (In,Ga) on the substrate at room temperature.

22. The method of claim 21, including the step of annealing the thin-film precursors at a low temperature for a period of time before said step of annealing the thin-film precursors in the presence of Se at a moderate temperature.

23. The method of claim 22, wherein said low temperature is in the range of 50°

-150°

C.

24. The method of claim 22, wherein said low temperature is about 100°

C.

25. The method of claim 22, wherein said time period is in the range of five to eleven minutes.

26. The method of claim 22, wherein said time period is about eight minutes.