Method of making a hybride substrate having a thin silicon carbide membrane layer

• US 6,699,770 B2
• Filed: 02/28/2002
• Issued: 03/02/2004
• Est. Priority Date: 03/01/2001
• Status: Expired due to Fees

• Current Assignee: Astralux, Inc.
• Original Assignee: Astralux, Inc.
• Inventors: Torvik, John Tarje
• Primary Examiner(s): Whitehead, Jr., Carl
• Assistant Examiner(s): Blum, David S
• Application Number:
  US10/086,016
• Publication Number:
  US 20020123204A1
• Time in Patent Office: 733 Days
• Field of Search: 438/406, 438/412, 438/455, 438/459, 438/479, 438/526
• US Class Current: 438/406
• CPC Class Codes: H01L 21/76256 using silicon etch back techniques, e.g. BESOI, ELTRAN

Abstract

A hybrid semiconductor substrate assembly is made by first forming a silicon oxide (SiO_x) layer within a silicon carbide wafer, thus forming a silicon carbide membrane on top of the silicon oxide layer and on a surface of the silicon carbide wafer. Optionally, the silicon oxide layer is then thermally oxidized in the presence of steam or oxygen. A substrate-of-choice is then wafer bonded to the silicon carbide membrane, optionally in the presence of a wetting layer that is located intermediate the substrate-of-choice and the silicone carbide membrane, the wetting layer containing silicon. The silicon oxide layer is then removed by hydrofluoric acid etching, to thereby provide a hybrid semiconductor substrate assembly that includes the substrate-of-choice wafer bonded to the silicon carbide membrane. The hybrid semiconductor substrate assembly is then annealed. The method is repeated a plurality of times, to thereby provide a plurality of hybrid semiconductor substrate assemblies, each assembly including a substrate-of-choice wafer bonded to a silicon carbide membrane. Optionally, an annealing step may be provided after the silicon oxide layer is formed and prior to wafer bonding.

Claims

1. A method of making a hybrid substrate assembly comprising the steps of:

providing a semiconductor wafer having a first composition;

implanting an oxide layer within said semiconductor wafer to thereby form a semiconductor membrane on a surface of said semiconductor wafer;

providing a substrate-of-choice having a second composition that is different than said first composition;

wafer bonding said substrate-of-choice to said semiconductor membrane; and

etching said oxide layer to separate said semiconductor membrane from a remainder of said semiconductor wafer and thereby provide a hybrid substrate assembly that includes said substrate-of-choice wafer bonded to said semiconductor membrane.

2. The method of claim 1 wherein the etching step removes at least substantially the oxide layer from the substrate-of-choice and the semiconductor membrane and including the step of:

aligning a crystalline construction of said substrate-of-choice to a crystalline construction of said semiconductor membrane prior to said wafer bonding step.

3. The method of claim 1 including the step of:

providing a wetting layer intermediate said substrate-of-choice and said semiconductor membrane, said wetting layer having an element that is common to said first composition and said second composition.

4. The method of claim 1 including the step of:

thermally oxidizing said oxide layer prior to said wafer-bonding step, wherein a temperature of the oxidizing step is greater than a temperature of the implanting step and wherein the temperature of the oxidizing step is at least about 600°

C.

5. The method of claim 1 wherein said step of implanting said oxide layer within said semiconductor wafer and said step of etching said oxide layer respectively comprise an oxygen-implantation step and an acid-etching step.

6. The method of claim 4 including the step of:

providing a wetting layer intermediate said substrate-of-choice and said semiconductor membrane prior to performing said wafer-bonding step.

7. The method of claim 1 including the step of:

subjecting said semiconductor membrane to a heating step, wherein a temperature of the heating step is greater than a temperature of the implanting step, wherein the heating step occurs after the implanting step and before the etching step, and wherein the temperature of the heating step is at least about 600°

C.

8. The method of claim 7 including the step of:

thermally oxidizing said oxide layer prior to said etching step.

9. The method of claim 8 wherein said step of implanting said oxide layer within said semiconductor wafer and said step of etching said oxide layer respectively comprise an oxygen-implantation step and an acid-etching step.

10. The method of claim 9 including the step of:

providing a wetting layer intermediate said substrate-of-choice and said semiconductor membrane prior to performing said wafer-bonding step.

11. The method of claim 1 wherein an etchant is used in the etching step and wherein the semiconductor wafer is resistant to the etchant while the oxide layer is susceptible to the etchant and further including the step of:

repeating said implanting step, said wafer bonding step, and said etching step a plurality of times relative to a plurality of substrates-of-choice, to thereby provide a plurality of hybrid substrate assemblies that each include a substrate-of-choice wafer bonded to a semiconductor membrane.

12. A method of making a hybrid substrate assembly comprising the steps of:

providing a wafer selected from SiC polytypes such as 6H—

SiC, 4H—

SiC, 3C—

SiC and 15R—

SiC;

forming a SiO_x layer within said wafer to thereby form a wafer membrane on a surface of said wafer;

providing a substrate-of-choice;

wafer bonding said substrate-of-choice to said wafer membrane; and

etching said SiO_x layer to thereby provide a hybrid substrate assembly that includes said substrate-of-choice wafer bonded to said wafer membrane, wherein the SiC polytype wafer is resistant to the etchant in the etching step while the SiO_x layer is susceptible to the etchant.

13. The method of claim 12 including the step of:

thermally oxidizing said SiO_x layer prior to said etching step, wherein a temperature of the oxidizing step is greater than a temperature of the forming step and the temperature of the oxidizing step is at least about 600°

C.

14. The method of claim 12 including the step of:

providing a wetting layer intermediate said substrate-of-choice and said wafer membrane prior to said wafer-bonding step.

15. The method of claim 14 wherein said wetting layer contains silicon.

16. The method of claim 15 wherein said wetting layer is a layer that contains silicon, such as Si₃N₄.

17. The method of claim 12 including the step of:

heating said wafer after said forming step, wherein a temperature of the heating step is greater than a temperature of the forming step and wherein the temperature of the heating step is at least about 600°

C.

18. The method of claim 12 wherein the etching step removes at least substantially the SiO_x layer from the substrate-of-choice and the wafer membrane.

19. The method of claim 12 wherein said substrate-of-choice is selected from a group including Si, SiO₂, polycrystalline SiC, sapphire, polycrystalline AlN, crystalline MN, diamond and Si₃N₄.

20. The method of claim 12 wherein said wafer is SiC.

21. The method of claim 12 wherein an etchant is used in said etching step comprises etching said SiO_x layer in hydrofluoric acid.

22. The method of claim 12 wherein said step of forming said SiO_x layer within said wafer and said step of etching said SiO_x layer, respectively, comprise an oxygen-implantation step and an acid-etching step.

23. The method of claim 12 including the step of:

repeating said forming step, said wafer bonding step, and said etching step a plurality of times relative to a plurality of substrates-of-choice to thereby provide a plurality of hybrid substrate assemblies that each include a substrate-of-choice wafer bonded to a wafer membrane.

24. The method of claim 12 wherein SiO_x is SiO₂.

25. The method of claim 24 wherein said wafer membrane is one micrometer thick or less.

26. The method of claim 12 including the step of:

optimizing said wafer-bonding step by aligning a crystalline nature of said wafer and said substrate-of-choice prior to said wafer-bonding step.

27. A method of making a hybrid substrate assembly comprising the steps of:

providing a SiC wafer;

forming a SiO_x layer within said SiC wafer to thereby form a SiC membrane on a surface of said SiC wafer;

thermally oxidizing said SiO_x layer;

providing a substrate-of-choice;

providing a wetting layer that contains Si intermediate said substrate-of-choice and said SiC membrane;

wafer bonding said substrate-of-choice to said SiC membrane; and

etching said SiO_x layer to thereby provide a hybrid substrate assembly that includes said substrate-of-choice wafer bonded to said SiC membrane, wherein the thermally oxidizing step occurs before the etching step and wherein the SiC wafer is resistant to the etchant in the etching step while the SiO_x layer is susceptible to the etchant.

28. The method of claim 27 wherein said thermal oxidation step takes place in the presence of steam or oxygen and a temperature of the thermal oxidation step is greater than a temperature of the forming step and the temperature of the thermal oxidation step is at least about 600°

C.

29. The method of claim 27 wherein said wetting layer is Si₃N₄.

30. The method of claim 27 including the step of:

heating said SiC wafer after said forming step, wherein a temperature of the heating step is greater than a temperature of the forming step and the temperature of the heating step is at least about 600°

C.

31. The method of claim 27 wherein the etching step removes substantially completely the SiO_x layer from the SiC membrane and SiC wafer.

32. The method of claim 27 wherein said substrate-of-choice is selected from a group including Si, SiO₂, polycrystalline SiC, sapphire, polycrystalline AlN, crystalline AlN, diamond and Si₃N₄.

33. The method of claim 27 wherein said wafer is selected from SiC polytypes.

34. The method of claim 27 wherein said etching step comprises etching said SiO_x layer in hydrofluoric acid.

35. The method of claim 27 wherein said step of forming said SiO_x layer within said SiC wafer and said step of etching said SiO_x layer respectively comprise an oxygen-implantation step and an acid-etching step.

36. The method of claim 27 including the step of:

repeating said forming step, said thermal oxidizing step, said providing a wetting layer step, said wafer-bonding step, and said etching step a plurality of times relative to a plurality of substrates-of-choice to thereby provide a plurality of hybrid substrate assemblies that each include a substrate-of-choice wafer bonded to a SiC membrane.

37. The method of claim 27 wherein said SiC membrane is about one micro meter thick.

38. The method of claim 27 including the steps of:

determining a crystalline structure of said SiC wafer and a crystalline structure of said substrate-of-choice; and

physically aligning said crystalline structure of said SiC membrane to said crystalline structure of said SiC wafer prior to said wafer-bonding step.

39. A method of making a hybrid substrate assembly comprising the steps of:

providing a wafer selected from SiC polytypes such as 6H—

SiC, 4H—

SiC, 3C—

SiC, and 15R—

SiC;

forming a SiO_x layer within said wafer by means of oxygen implantation, to thereby form a wafer membrane on a surface of said wafer;

thermally oxidizing said SiO_x layer to grow the SiO_x layer;

providing a substrate-of-choice;

providing a wetting layer that contains Si intermediate said substrate-of-choice and said wafer membrane;

wafer bonding said substrate-of-choice to said wafer membrane; and

etching said SiO_x layer to thereby provide a hybrid substrate assembly that includes said substrate-of-choice wafer bonded to said wafer membrane, wherein the thermally oxidizing step occurs before the etching step.

40. The method of claim 39 wherein said thermal oxidation step takes place in the presence of steam or oxygen and wherein a temperature of the thermal oxidation step is greater than a temperature of the forming step.

41. The method of claim 39 including the step of:

heating said wafer after said forming step, wherein a temperature of the heating step is greater than a temperature of the forming step and the temperature of the heating step is at least about 600°

C.

42. The method of claim 39 including the step of:

annealing said hybrid substrate assembly.

43. The method of claim 39 wherein said substrate-of-choice is selected from a group including Si, SiO₂, polycrystalline SiC, sapphire, polycrystalline AlN, crystalline AlN, diamond and Si₃N₄.

44. The method of claim 39 wherein the wafer is resistant to the etchant in the etching step while the SiO_x layer is susceptible to the etchant and further including the step of:

repeating said forming step, said thermal oxidation step, said providing a wetting layer step, said wafer bonding step, and said etching step a plurality of times relative to said wafer and relative to a plurality of substrates-of-choice, to thereby provide a plurality of hybrid substrate assemblies that each include a substrate-of-choice wafer bonded to a wafer membrane.

45. The method of claim 39 wherein said wafer membrane is no greater that about one micro meter thick.

46. The method of claim 39 including the steps of:

determining a first crystalline structure of said wafer;

determining a second crystalline structure of said substrate-of-choice;

determining an alignment of said first crystalline structure to said second crystalline structure that will enhance wafer bonding of said wafer membrane to said substrate-of-choice; and

aligning said wafer membrane with respect to said substrate-of-choice in accordance with said determined alignment prior to said wafer-bonding step.

47. The method of making a hybrid substrate assembly comprising the steps of:

providing a semiconductor wafer having a first composition;

implanting an oxide layer within said semiconductor wafer to thereby form a semiconductor membrane on a surface of said semiconductor wafer;

thermally oxidizing the oxide layer to grow the oxide layer;

providing a substrate-of-choice having a second composition that is different than said first composition;

bonding said substrate-of-choice to said semiconductor membrane; and

etching said oxide layer to separate said semiconductor membrane from a remainder of said semiconductor water and thereby provide a hybrid substrate assembly that includes said substrate-of-choice wafer bonded to said semiconductor membrane, wherein the thermal oxidizing step occurs after the implanting step and before the etching step.

48. The method of claim 47 including the step of:

aligning a crystalline construction of said substrate-of-choice to a crystalline construction of said semiconductor membrane prior to said bonding step.

49. The method of claim 47 including the step of:

providing a wetting layer intermediate said substrate-of-choice and said semiconductor membrane, said wetting layer having an element that is common to said first composition and said second composition.

50. The method of claim 47 wherein a temperature of the thermally oxidizing step is greater than a temperature of the implanting step and at least about 600°

C.

51. The method of claim 47 wherein said step of implanting said oxide layer within said semiconductor wafer and said step of etching said oxide layer respectively comprise an oxygen-implantation step and an acid-etching step.

52. The method of claim 51 including the step of:

providing a wetting layer intermediate said substrate-of-choice and said semiconductor membrane prior to performing said bonding step.

53. The method of claim 47 further comprising:

annealing said hybrid substrate assembly to repair any ion implantation induced damage from the implanting step, wherein the annealing step occurs before the etching step.

54. The method of claim 53 wherein the oxide layer is susceptible to the etchant while the semiconductor wafer is resistant to the etchant.

55. The method of claim 53 wherein said step of implanting said oxide layer within said semiconductor wafer and said step of etching said oxide layer respectively comprise an oxygen-implantation step and an acid-etching step.

56. The method of claim 55 including the step of:

providing a wetting layer intermediate said substrate-of-choice and said semiconductor membrane prior to performing said bonding step.

57. The method of claim 54 including the step of:

repeating said implanting step, said wafer bonding step, and said etching step a plurality of times relative to a plurality of substrates-of-choice, to thereby provide a plurality of hybrid substrate assemblies that each include a substrate-of-choice wafer bonded to a semiconductor membrane.

58. The method of claim 47 wherein the bonding step comprises wafer bonding of the semiconductor wafer to the substrate-of-choice.

59. The method of claim 58 wherein the wafer bonding step comprises heating the semiconductor wafer and the substrate-of-choice.

60. The method of claim 59 wherein the wafer bonding step comprises:

physically contacting opposing surfaces of the substrate-of-choice and the semiconductor membrane to form an intermediate structure; and

the heating step comprises;

heating the intermediate structure to cause crystallites within the opposing surfaces to fuse together.

61. The method of claim 60 wherein in the heating step the opposing surfaces are under pressure and wherein the heating step is performed in the presence of a forming gas.

62. The method of claim 61 wherein the forming gas is a mixture of molecular hydrogen and molecular nitrogen.

63. A hybrid substrate assembly formed by the process of claim 47.