Surface planarization of high temperature superconductors

• US 6,251,835 B1
• Filed: 05/06/1998
• Issued: 06/26/2001
• Est. Priority Date: 05/08/1997
• Status: Expired due to Term

• Current Assignee: Lumentum Operations, LLC (Lumentum Holdings Inc.)
• Original Assignee: Epion Corporation (Tokyo Electron Limited)
• Inventors: Wu, Judy Z., Chu, Wei-Kan
• Primary Examiner(s): Utech, Benjamin L.
• Assistant Examiner(s): ANDERSON, MATTHEW A
• Application Number:
  US09/073,786
• Time in Patent Office: 1,147 Days
• Field of Search: 117/4, 117/7, 117/8, 117/9, 117/3, 505/411, 505/480, 505/500, 438/710, 438/722, 438/720
• US Class Current: 505/411
• CPC Class Codes: B82Y 15/00 Nanotechnology for interacting, sensing or actuating, e.g. quantum dots as markers in protein assays or molecular motors
• CPC Class Codes: C30B 29/22 Complex oxides
• CPC Class Codes: C30B 29/225 based on rare earth copper oxides, e.g. high T-superconductors
• CPC Class Codes: C30B 31/22 by ion-implantation
• CPC Class Codes: C30B 33/00 After-treatment of single crystals or homogeneous polycrystalline material with defined structure C30B31/00 takes precedence
• CPC Class Codes: H10N 60/0661 Processes performed after copper oxide formation, e.g. patterning

Abstract

Planarizing High Temperature Superconductor (HTS) surfaces, especially HTS thin film surfaces is crucial for HTS thin film device processing. Disclosed is a method of surface planarization for HTS film. The method includes first smoothing the HTS surface by Gas Cluster Ion Beam bombardment, followed by annealing in partial pressure of oxygen to regrow the damaged surface layer. A rough HTS surface can be planarized down to a smoothness with a standard deviation of one nanometer or better.

Claims

1. A method of processing a substrate comprising a high temperature crystalline superconductor surface, having a surface roughness R₀ and a transition temperature T_c, the method comprising:

(a) contacting the surface of the substrate with gas cluster ions, said cluster ions comprising at least one atomic species different from at least one atomic species in said superconductor surface, to reduce both the surface roughness and the crystallinity of the surface and to impair the high temperature superconducting properties of said surface; and

(b) processing the surface of the substrate to restore the crystallinity and to at least partially restore the high temperature superconductivity of the surface.

2. The method of claim 1, wherein said processing step comprises thermally annealing the surface to restore crystallinity.

3. The method of claim 1, wherein said processing step comprises removing a shallow layer of the surface to expose underlying material having higher crystallinity.

4. The method of claim 1, wherein the superconductor surface comprises a YBCO type of superconductor.

5. The method of claim 1, wherein the contacting in step (a) comprises bombarding with gas cluster ions of having energies greater than 7 keV and less than 200 keV.

6. The method of claim 5, wherein the gas cluster ions have energies greater than 10 keV and less than 100 keV.

7. The method of claim 5, wherein the gas cluster ions have energies in the range from 15 to 35 keV.

8. The method of claim 1 further comprising:

(c) depositing a single crystal layer on the surface.

9. The method of claim 8 further comprising:

(d) processing said single crystal layer to configure structures thereon.

10. The method of claim 9, wherein said second processing step comprises smoothing said single crystal layer, and annealing the smoothed single crystal layer.

11. The method of claim 1, wherein said contacting step comprises bombarding said surface with gas cluster ions comprising a cluster in a range between 10 and 30 KeV with a total dose of 10¹⁴ to 2×

10¹⁶ clusters/cm².

12. The method of claim 1, wherein said annealing step comprises annealing the surface under a partial oxygen atmosphere.

13. The method of claim 12, wherein said annealing is carried out at approximately 800°

C. under oxygen partial pressure of approximately 100 mTorr for approximately 30 minutes followed by an approximately 450°

C. and 200 mTorr oxygen pressure for approximately 30 minutes.

14. The method of claim 12, wherein said annealing is carried out at approximately 870°

C., 660°

C., and 450°

C. consecutively for approximately 35 minutes, each under flowing oxygen gas.

15. The method of claim 1, wherein said restored high temperature superconductivity occurs at a transition temperature near T_c.

28. The method of claim 13, wherein said restored high temperature superconductivity occurs at a transition temperature near T_c.

16. A method of processing a substrate comprising:

(a) depositing a crystalline high temperature superconductor surface layer on said substrate, said layer having a surface roughness R₀ and a transition temperature T_c;

(b) bombarding said surface layer with gas cluster ion, said cluster ions comprising at least one atomic species different from at least one atomic species in said superconductor surface, to reduce the surface roughness to R₁, wherein R₁ is less than R₀, and to reduce the crystallinity of the surface layer and to impair the high temperature superconducting properties of said surface layer; and

(c) processing the surface layer of the substrate to restore the crystallinity and to at least partially restore the high temperature superconductivity of the surface layer.

17. The method of claim 16, wherein said processing step comprises thermally annealing the surface to restore crystallinity.

18. The method of claim 17, wherein said annealing step comprises annealing the surface in partial oxygen.

19. The method of claim 18, wherein said annealing is carried out at approximately 800°

C. under oxygen partial pressure of approximately 100 mTorr for approximately 30 minutes followed by an approximately 450°

C. and 200 mTorr oxygen pressure for approximately 30 minutes.

20. The method of claim 18, wherein said annealing is carried out at approximately 870°

C., 660°

C., and 450°

C. consecutively for approximately 35 minutes, each under flowing oxygen gas.

21. The method of claim 16, wherein said processing step comprises removing a shallow layer of the surface to expose underlying material having higher crystallinity.

22. The method of claim 16, wherein said surface layer comprises a YBCO type of superconductor.

23. The method of claim 16 further comprising:

(d) depositing a single crystal layer on the surface.

24. The method of claim 23, wherein said single crystal layer comprises a superconducting layer.

25. The method of claim 23, further comprising:

(e) processing said single crystal layer to configure structures thereon.

26. The method of claim 23, wherein said single crystal layer comprises an insulating layer.

27. The method of claim 16, wherein said contacting step comprises bombarding said surface with gas cluster ions comprising a cluster in a range between 10 and 30 KeV with a total dose of 10¹⁴ to 2×

10¹⁶ clusters/cm².

29. A method of processing a substrate comprising a high temperature crystalline superconductor surface, having a surface roughness R₀, the method comprising:

(a) contacting the surface of the substrate with gas cluster ions, said cluster ions comprising at least one atomic species different from at least one atomic species in said superconductor surface, to reduce both the surface roughness and the crystallinity of the surface and the impair the high temperature superconducting properties of the surface; and

(b) processing the surface of the substrate to restore the crystallinity of the surface and to at least partially restore the superconducting properties of the surface.

30. The method of claim 29, wherein said processing step comprises thermally annealing the surface to restore crystallinity.

31. The method of claim 29, wherein said processing step comprises removing a shallow layer of the surface to expose underlying material having higher crystallinity.

32. The method of claim 29, wherein the superconductor surface comprises a YBCO type of superconductor.

33. The method of claim 29, wherein the contacting in step (a) comprises bombarding with gas cluster ions of having energies greater than 7 keV and less than 200 keV.

34. The method of claim 29 further comprising:

(c) depositing a single crystal layer on the surface.

35. The method of claim 34 further comprising:

(d) processing said single crystal layer to configure structures thereon.

36. The method of claim 35, wherein said second processing step comprises smoothing said single crystal layer, and annealing the smoothed single crystal layer.

37. The method of claim 29, wherein said contacting step comprises bombarding said surface with gas cluster ions comprising a cluster in a range between 10 and 30 KeV with a total dose of 10¹⁴ to 2×

10¹⁶ clusters/cm².

38. The method of claim 29, wherein said annealing step comprises annealing the surface under a partial oxygen atmosphere.

39. The method of claim 38, wherein said annealing is carried out at approximately 800°

C. under oxygen partial pressure of approximately 100 mTorr for approximately 30 minutes followed by an approximately 450°

C. and 200 mTorr oxygen pressure for approximately 30 minutes.

40. The method of claim 38, wherein said annealing is carried out at approximately 870°

C., 660°

C., and 450°

C. consecutively for approximately 35 minutes, each under flowing oxygen gas.

41. The method of claim 29, wherein said restored high temperature superconductivity occurs at a transition temperature near T_c.

42. A method of processing a substrate comprising:

(a) depositing a crystalline high temperature superconductor surface layer on said substrate, said layer having a surface roughness R₀;

(b) bombarding said surface layer with gas cluster ions, said cluster ions comprising at least one atomic species different from at least one atomic species in said superconductor surface, to reduce the surface roughness to R₁, wherein R₁ is less than R₀, and to reduce the crystallinity of the surface layer and to impair the high temperature superconducting properties of the surface layer; and

(c) processing the surface layer of the substrate to restore the crystallinity and to at least partially restore the high temperature superconducting properties of the surface layer.

43. The method of claim 42, wherein said processing step comprises thermally annealing the surface to restore crystallinity.

44. The method of claim 43, wherein said annealing step comprises annealing the surface in the partial oxygen.

45. The method of claim 44, wherein said annealing is carried out at approximately 800°

C. under oxygen partial pressure of approximately 100 mTorr for approximately 30 minutes followed by a approximately 450°

C. and 200 mTorr oxygen pressure for approximately 30 minutes.

46. The method of claim 44, wherein said annealing is carried out at approximately 870°

C., 660°

C., and 450°

C consecutively for approximately 35 minutes, each under flowing oxygen gas.

47. The method of claim 42, wherein said processing step comprises removing a shallow layer of the surface to expose underlying material having higher crystallinity.

48. The method of claim 42, wherein said surface layer comprises a YBCO type of superconductor.

49. The method of claim 42 further comprising:

(d) depositing a single crystal layer on the surface.

50. The method of claim 49, wherein said single crystal layer comprises an insulating layer.

51. The method of claim 49, wherein said single crystal layer comprises a superconducting layer.

52. The method of claim 49 further comprising:

(e) processing said single crystal layer to configure structures thereon.

53. The method of claim 49, wherein the gas cluster ions have energies greater than 10 keV and less than 100 keV.

54. The method of claim 49, wherein the gas cluster ions have energies in the range from 15 to 35 keV.

55. The method of claim 42, wherein said bombarding step comprises bombarding said surface with gas cluster ions comprising a cluster in a range between 10 and 30 KeV with a total dose of 10¹⁴ to 2×

10¹⁶ cluster/cm².

56. The method of claim 42, wherein said restored high temperature superconductivity occurs at a transition temperature near T_c.