High surface quality GaN wafer and method of fabricating same

• US 20030127041A1
• Filed: 10/17/2002
• Published: 07/10/2003
• Est. Priority Date: 06/08/2001
• Status: Active Grant

• Current Assignee: Wolfspeed, Inc.
• Original Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Inventors: Xu, Xueping, Vaudo, Robert P.
• Granted Patent: US 6,951,695 B2
• Time in Patent Office: Days
• US Class Current: 117/2
• CPC Class Codes: C09G 1/02 containing abrasives or grinding agents abrasives as such C09K3/14; polishing of semi-conductors H01L
• CPC Class Codes: C09K 3/1409 Abrasive particles per se preparation of diamond C01B32/25
• CPC Class Codes: C09K 3/1463 Aqueous liquid suspensions
• CPC Class Codes: C30B 25/02 Epitaxial-layer growth
• CPC Class Codes: C30B 29/403 AIII-nitrides
• 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: H01L 21/02005 Preparing bulk and homogeneous wafers
• CPC Class Codes: H01L 21/02019 Chemical etching
• CPC Class Codes: H01L 21/02024 Mirror polishing
• CPC Class Codes: H01L 21/30617 Anisotropic liquid etching
• CPC Class Codes: H01L 33/0075 comprising nitride compounds
• CPC Class Codes: Y10T 428/21 Circular sheet or circular blank

Abstract

Al_xGa_yIn_zN, wherein 0≦x≦1, 0≦y≦1, 0≦z≦1, and x+y+z=1, characterized by a root mean square surface roughness of less than 1 nm in a 10×10 μm²² area. The Al_xGa_yIn_zN may be in the form of a wafer, which is chemically mechanically polished (CMP) using a CMP slurry comprising abrasive particles, such as silica or alumina, and an acid or a base. High quality Al_xGa_yIn_zN wafers can be fabricated by steps including lapping, mechanical polishing, and reducing internal stress of said wafer by thermal annealing or chemical etching for further enhancement of its surface quality. CMP processing may be usefully employed to highlight crystal defects of an Al_xGa_yIn_zN wafer.

Claims

1. A wafer comprising Al_xGa_yIn_zN wherein 0≦

x≦

1, 0≦

y≦

1, 0≦

z≦

1 and x+y+z=1, characterized by a root mean square (RMS) surface roughness of less than 1 nm in a 10×

10 μ

m² area.

2. The wafer of claim 1, wherein the RMS surface roughness of said wafer is less than 0.7 nm in a 10×

10 μ

m² area.

3. The wafer of claim 1, wherein the RMS surface roughness of said wafer is less than 0.5 nm in a 10×

10 μ

m² area.

4. The wafer of claim 1, wherein the RMS surface roughness of said wafer is at least less than 0.4 nm in a 2×

2 μ

m² area.

5. The wafer of claim 1, wherein the RMS surface roughness of said wafer is less than 0.2 nm in a 2×

2 μ

m² area.

6. The wafer of claim 1, wherein the RMS surface roughness of said wafer is less than 0.15 nm in a 2×

2 μ

m² area.

7. The wafer of claim 1, characterized by a step structure when observed with an atomic force microscope.

8. The wafer of claim 1, wherein the crystal defects are visible as small pits with diameters of less than 1 μ

m.

9. The wafer of claim 1, formed by chemically mechanically polishing (CMP) an Al_xGa_yIn_zN wafer blank, using a silica- or alumina-containing CMP slurry.

10. An epitaxial Al_xGa_yIn_zN crystal structure, comprising an epitaxial Al_x′

Ga_y′

In_z′

N thin film grown on a wafer comprising Al_xGa_yIn_zN wherein 0≦

x′

≦

1, 0≦

y′

≦

1, 0≦

z′

≦

1, x′

+y′

+z′

=1, 0≦

x≦

1, 0≦

y≦

1, 0≦

z≦

1, said wafer being characterized by a root mean square (RMS) surface roughness of less than 1 nm in a 10×

10 μ

m² area.

11. The epitaxial Al_xGa_yIn_zN crystal structure of claim 10, comprising a wurtzite crystalline thin film.

12. The epitaxial Al_xGa_yIn_zN crystal structure of claim 10, where the epitaxial Al_x′

Ga_y′

In_z′

N thin film has the same composition as the wafer comprising Al_xGa_yIn_zN.

13. The epitaxial Al_xGa_yIn_zN crystal structure of claim 10, where the epitaxial Al_x′

Ga_y′

In_z′

N thin film has a different composition from the wafer comprising Al_xGa_yIn_zN.

14. The epitaxial Al_xGa_yIn_zN crystal structure of claim 10, where the epitaxial Al_x′

Ga_y′

In_z′

N thin film has a graded composition.

15. An optoelectronic device comprising at least one epitaxial Al_x′

Ga_y′

In_z′

N crystal structure grown on a wafer comprising Al_xGa_yIn_zN, wherein 0≦

x′

≦

1, 0≦

y′

≦

1, 0≦

z′

≦

1, x′

+y′

+z′

=1, 0≦

x≦

1, 0≦

y≦

1, 0≦

z≦

1, and x+y+z=1, said wafer being characterized by a root mean square (RMS) surface roughness of at least less than 1 nm in a 10×

10 μ

m² area.

16. The optoelectronic device of claim 15, wherein the optoelectronic device is a light emitting diode.

17. The optoelectronic device of claim 15, wherein the optoelectronic device is a blue light laser diode.

18. The optoelectronic device of claim 15, wherein the optoelectronic device is incorporated into a light emitting diode.

19. The optoelectronic device of claim 15, wherein the optoelectronic device is incorporated into a magneto-optic memory device.

20. The optoelectronic device of claim 15, wherein the optoelectronic device is incorporated into a full color light emitting display.

21. The optoelectronic device of claim 15, wherein the optoelectronic device is incorporated into a DVD device.

22. A microelectronic device comprising at least one epitaxial Al_x′

Ga_y′

In_z′

N crystal structure grown on a wafer comprising Al_xGa_yIn_zN wherein 0≦

x′

≦

1, 0≦

y′

≦

1, 0≦

z′

≦

1, x′

+y′

+z′

=1, 0≦

x≦

1, 0≦

y≦

1 , 0≦

z≦

1, and x+y+z=1, said wafer being characterized by a root mean square (RMS) surface roughness of at least less than 1 nm in a 10×

10 μ

m² area.

23. An epitaxial Al_x′

Ga_y′

In_z′

N crystal boule grown on a wafer comprising Al_xGa_yIn_zN, 0≦

x′

≦

1, 0≦

y′

≦

1, 0≦

z′

≦

1, x′

+y′

+z′

=1, 0≦

x≦

1, 0≦

y≦

1, 0≦

z≦

1, and x+y+z=1, said wafer being characterized by a root mean square (RMS) surface roughness of at least less than 1 nm in a 10×

10 μ

m² area.

24. The epitaxial Al_x′

Ga_y′

In_z′

N crystal boule of claim 23, where the boule is grown in gas phase.

25. The epitaxial Al_x′

Ga_y′

In_z′

N crystal boule of claim 23, where the boule is grown in liquid phase.

26. A method of chemically mechanically polishing (CMP) an Al_xGa_yIn_zN wafer, wherein 0≦

x≦

1, 0≦

y≦

1, 0≦

z≦

1, and x+y+z=1, using a CMP slurry comprising;

abrasive amorphous silica particles;

at least one acid; and

optionally, at least one oxidation agent;

wherein the CMP slurry has an acidic pH.

27. The method of claim 26, wherein the CMP slurry comprises fumed silica having an average particle size in a range of from about 10 nm to about 100 nm.

28. The method of claim 26, wherein the CMP slurry comprises colloidal silica having an average particle size in a range from about 10 nm to about 100 nm.

29. The method of claim 26, wherein the CMP slurry comprises an oxidation agent.

30. The method of claim 29, wherein the oxidation agent comprises an oxidant selected from the group consisting of hydrogen peroxide and dichloroisocyanuric acid.

31. The method of claim 26, wherein the acid comprises hydrochloric acid.

32. The method of claim 26, wherein the CMP slurry has a pH in a range of from about 0.6 to about 3.

33. The method of claim 26, wherein the CMP slurry has a pH in a range of from about 0.8 to about 2.5.

52. The method claim of 26, wherein the CMP slurry is filtered to remove particles larger than 100 nm in diameter before delivery to the polishing pad.

34. A method of chemically mechanically polishing an Al_xGa_yIn_zN wafer, wherein 0≦

x≦

1, 0≦

y≦

1, 0≦

z≦

1, and x+y+z=1, using a CMP slurry comprising;

abrasive colloidal alumina particles;

at least one acid; and

optionally, at least one oxidation agent;

wherein the CMP slurry has an acidic pH.

35. The method of claim 34, wherein the CMP slurry comprises colloidal alumina having an average particle size in a range of from about 10 nm to about 100 nm.

36. The method of claim 34, wherein the CMP slurry comprises an oxidation agent.

37. The method of claim 36, wherein the oxidation agent comprises comprises an oxidant selected from the group consisting of hydrogen peroxide and dichloroisocyanuric acid.

38. The method of claim 34, wherein the acid comprises hydrochloric acid.

39. The method of claim 34, wherein the CMP slurry has a pH in a range of from about 3 to about 5.

53. The method claim of 34, wherein the CMP slurry is filtered to remove particles larger than 100 nm in diameter before delivery to the polishing pad.

40. A method of chemically mechanically polishing an Al_xGa_yIn_zN wafer, wherein 0≦

x≦

1, 0≦

y≦

1, 0≦

z≦

1, and x+y+z=1, using a CMP slurry comprising;

amorphous silica particles;

at least one base; and

optionally, at least one oxidization agent,

wherein the CMP slurry has a basic pH.

41. The method of claim 40, wherein the CMP slurry comprises fumed silica having an average particle size in a range of from about 10 nm to about 100 mn.

42. The method of claim 40, wherein the CMP slurry comprises colloidal silica having an average particle size in a range of from about 10 nm to about 100 nm.

43. The method of claim 40, wherein the CMP slurry comprises a base selected from the group consisting of ammonia, alkanolamines, and hydroxides.

44. The method of claim 40, wherein the CMP slurry comprises ammonia.

45. The method of claim 40, wherein the CMP slurry comprises an alkanolamine.

46. The method of claim 40, wherein the CMP slurry comprises a hydroxide selected from the group consisting of KOH and NaOH.

47. The method of claim 40, wherein the CMP slurry comprises an oxidation agent.

48. The method of claim 47, wherein the oxidation agent comprises hydrogen peroxide.

49. The method of claim 47, wherein the oxidation agent comprises dichloroisocyanuric acid.

50. The method of claim 40, wherein the CMP slurry has a pH in a range of from about 7 to about 14.

51. The method of claim 40, wherein the CMP slurry has a pH in a range of from about 10 to about 11.

54. The method claim of 40, wherein the CMP slurry is filtered to remove particles larger than 100 nm in diameter before delivery to the polishing pad.

55. A method of determining crystal defect density in an Al_xGa_yIn_zN wafer, wherein 0≦

x≦

1, 0≦

y≦

1, 0≦

z≦

1, and x+y+z=1, comprising the steps of;

providing an Al_xGa_yIn_zN wafer;

chemically mechanically polishing said wafer, using a CMP slurry comprising abrasive amorphous silica articles, at least one acid, and optionally at least one oxidization agent, wherein said CMP slurry has an acidic pH;

cleaning and drying the polished Al_xGa_yIn_zN wafer; and

scanning the wafer with an atomic force microscope or a scanning electron microscope to determine defect density in said wafer.

56. A method of fabricating wafers comprising Al_xGa_yIn_zN, wherein 0≦

x≦

1, 0≦

y≦

1, 0≦

z≦

1, and x+y+z=1, comprising the steps of;

providing an Al_xGa_yIn_zN wafer blank having thickness in a range from about 100μ

m to about 1000μ

m;

optionally, reducing the internal stress of the Al_xGa_yIn_zN wafer blank;

optionally, lapping the Al_xGa_yIn_zN wafer blank at a back side thereof, using a lapping slurry comprising abrasives having an average particle size in a range of from about 5 μ

m to about 15 μ

m;

optionally, mechanically polishing the Al_xGa_yIn_zN wafer blank at the back side thereof, using a mechanical polishing slurry comprising abrasives having average particle size in a range of from about 0.1 μ

m to about 6 μ

m;

optionally, lapping the Al_xGa_yIn_zN wafer blank at a front side thereof, using a lapping slurry comprising abrasives having an average particle size in a range of from about 5 μ

m to about 15 μ

m;

optionally, mechanically polishing the Al_xGa_yIn_zN wafer blank at the front side thereof, using a mechanical polishing slurry comprising abrasives having average particle size in a range of from about 0.1μ

m to about 6 μ

m;

chemically mechanically polishing the Al_xGa_yIn_zN wafer at the front side thereof, using a CMP slurry comprising at least one chemical reactant and abrasive particles having average particle size of less than 200 nm; and

optionally, etching the Al_xGa_yIn_zN wafer in a mild etching condition to further reduce internal stresses of the Al_xGa_yIn_zN wafer, to improve surface quality, and to produce a matte finish at the back side of the wafer,

wherein the Al_xGa_yIn_zN wafer so fabricated has a surface roughness characterized by a root mean square (RMS) surface roughness of less than 1 nm in a 10×

10 μ

m² area at the front side of the wafer.

57. The method of claim 56, wherein the Al_xGa_yIn_zN wafer blank is produced by the steps of:

growing a thick Al_xGa_yIn_zN film on a foreign substrate; and

removing the foreign substrate from the thick Al_xGa_yIn_zN film.

58. The method of claim 56, wherein the Al_xGa_yIn_zN wafer blank is produced by the steps of:

growing an Al_xGa_yIn_zN boule; and

slicing the Al_xGa_yIn_zN boule.

59. The method claim of 58, where the Al_xGa_yIn_zN boule is sliced so that the wafer blank surface is perpendicular to the c-axis.

60. The method claim of 58, where the Al_xGa_yIn_zN boule is sliced so that the wafer blank surface comprises a surface selected from the group consisting of:

Al_xGa_yIn_z-terminated surfaces of Al_xGa_yIn_zN in an (0001) orientation;

N-terminated surfaces of Al_xGa_yIn_zN in an (0001) orientation;

offcuts of Al_xGa_yIn_z-terminated surfaces of Al_xGa_yIn_zN in an (0001) orientation;

offcuts of N-terminated surfaces of Al_xGa_yIn_zN in an (0001) orientation;

A-plane surfaces;

M-plane surfaces;

R-plane surfaces;

offcuts of A-plane surfaces;

offcuts of M-plane surfaces; and

offcuts of R-plane surfaces.

61. The method of claim 56, wherein the internal stresses of the Al_xGa_yIn_zN wafer are reduced by thermally annealing said wafer.

62. The method of claim 56, wherein the internal stresses of the Al_xGa_yIn_zN wafer are reduced by chemically etching.

63. The method of claim 62, wherein surface material of less than 100μ

m thickness is removed from the Al_xGa_yIn_zN wafer.

64. The method of claim 62, wherein the Al_xGa_yIn_zN wafer is chemically etched by strong acid at a temperature above 150°

C.

65. The method of claim 64, wherein the strong acid is selected from the group consisting of sulfuric acid, phosphoric acid, and combinations thereof.

66. The method of claim 62, wherein the Al_xGa_yIn_zN wafer is chemically etched by a strong molten base at a temperature above 150°

C.

67. The method of claim 66, wherein the strong molten base is selected from the group consisting of molten LiOH, molten NaOH, molten KOH, molten RbOH, molten CsOH, and combinations thereof.

68. The method of claim 56, wherein the Al_xGa_yIn_zN wafer blank is lapped by a lapping slurry comprising abrasives selected from the group consisting of diamond powders, silicon carbide powders, boron carbide powders, and alumina powders.

69. The method of claim 56, wherein the lapping slurry comprises diamond powder having an average particle size in a range of from about 6μ

m to about 15 μ

m.

70. The method of claim 56, wherein the Al_xGa_yIn_zN wafer blank is lapped by two or more lapping slurries, with each subsequent lapping slurry comprising abrasives of a correspondingly smaller average size.

71. The method of claim 70, wherein the Al_xGa_yIn_zN wafer blank is lapped by a first lapping slurry comprising abrasives of an average particle size of from about 14 μ

m to about 16 μ

m, and by a second lapping slurry comprising abrasives of an average particle size of from about 5 μ

m to about 7 μ

m.

72. The method of claim 56, wherein the mechanical polishing slurry comprises abrasives selected from the group consisting of diamond powders, silicon carbide powders, boron carbide powders, and alumina powders.

73. The method of claim 56, wherein the mechanical polishing slurry comprises diamond powders having an average particle size in a range of from about 0.1 μ

m to about 6 μ

m.

74. The method of claim 56, wherein the Al_xGa_yIn_zN wafer blank is mechanically polished by two or more mechanical polishing slurries, with each subsequent mechanical polishing slurry comprising abrasives of a progressively smaller average size.

75. The method of claim 74, wherein the Al_xGa_yIn_zN wafer blank is mechanically polished by a first mechanical polishing slurry comprising abrasives of an average size of from about 2.5 μ

m to about 3.5 μ

m, by a second mechanical polishing slurry comprising abrasives of an average size of from about 0.75 μ

m to about 1.25 μ

m, by a third mechanical polishing slurry comprising abrasives of an average size of from about 0.35 μ

m to about 0.65 μ

m, by a fourth mechanical polishing slurry comprising abrasives of an average size of from about 0.2 μ

m to about 0.3 μ

m, and by a fifth mechanical polishing slurry comprising abrasives of an average size of from about 0.1 μ

m to about 0.2 μ

m.

76. The method of claim 56, wherein the CMP slurry is acidic, and has a pH in a range of from about 0.5 to about 4.

77. The method of claim 56, wherein the CMP slurry is basic, and has a pH in a range of from about 8 to about 13.5.

78. The method claim of 56, wherein the mild etching condition is selected from the group consisting of etching in aqueous acid solution and etching in aqueous base solution at a temperature below 100°

C.

79. The method claim of 78, wherein the acid is selected from group consisting of aqueous hydrofluoric acid, nitric acid, sulfuric acid, phosphoric acid, and combinations thereof.

80. The method claim of 78, wherein the base is selected from group consisting of aqueous LiOH, NaOH, KOH, RbOH, CsOH, and combinations thereof.

81. Al_xGa_yIn_zN, wherein 0≦

x≦

1, 0≦

y≦

1, 0≦

z≦

1, and x+y+z=1, characterized by a root mean square (RMS) surface roughness of less than 1 nm in a 10×

10 μ

m² area on a surface thereof, and said surface is selected from the group consisting of;

Al_xGa_yIn_z-terminated surfaces of Al_xGa_yIn_zN in an (0001) orientation;

N-terminated surfaces of Al_xGa_yIn_zN in an (0001) orientation;

offcuts of Al_xGa_yIn_z-terminated surfaces of Al_xGa_yIn_zN in an (0001) orientation;

offcuts of N-terminated surfaces of Al_xGa_yIn_zN in an (0001) orientation;

A-plane surfaces;

M-plane surfaces;

R-plane surfaces;

offcuts of A-plane surfaces;

offcuts of M-plane surfaces; and

offcuts of R-plane surfaces.

82. A method of fabricating a laser facet on an article formed of Al_xGa_yIn_zN, wherein 0≦

x≦

1, 0≦

y≦

1, 0≦

z≦

1, and x+y+z=1, comprising chemically mechanically polishing said article at a surface thereof using a chemical mechanical polishing slurry including silica and/or alumina abrasive particles, and an acid or base, wherein said chemically mechanically polishing step is carried out to impart to said surface a root mean square (RMS) surface roughness of less than 1 nm in a 10×

10 μ

m² area thereof.

83. A method of chemically mechanically polishing Al_xGa_yIn_zN, wherein 0≦

x≦

1, 0≦

y≦

1, 0≦

z≦

1, and x+y+z=1, using a chemical mechanical polishing slurry including silica and/or alumina abrasive particles, and an acid or base, wherein the chemically mechanically polishing step is carried out to impart to the surface a root mean square (RMS) surface roughness of less than 1 nm in a 10×

10 μ

m² area thereof.

84. The method of claim 83, wherein said Al_xGa_yIn_zN is in a wafer.

85. The method of claim 84, wherein said chemically mechanically polishing step is carried out in fabricating the wafer in a wafer fab.

86. The method of claim 84, wherein said chemically mechanically polishing step is carried out for planarizing the wafer.

87. The method of claim 84, wherein said chemically mechanically polishing step is carried out for replanarizing the wafer.

88. The method of claim 84, wherein said chemically mechanically polishing step is carried out in reworking the wafer to remove an undesired layer or material therefrom.

89. The method of claim 83, wherein said chemically mechanically polishing step is carried out for shaping of said Al_xGa_yIn_zN to counteract bow or other deformation or mis-shaping that would in the absence of such step be manifested in the processing of said Al_xGa_yIn_zN.

90. GaN, characterized by a root mean square (RMS) surface roughness of less than 1 nm in a 10×

10 μ

m² area on a surface thereof, and said surface is selected from the group consisting of;

Ga-terminated surfaces of GaN in an (0001) orientation;

N-terminated surfaces of GaN in an (0001) orientation;

offcuts of Ga-terminated surfaces of GaN in an (0001) orientation;

offcuts of N-terminated surfaces of GaN in an (0001) orientation;

A-plane surfaces;

M-plane surfaces;

R-plane surfaces;

offcuts of A-plane surfaces;

offcuts of M-plane surfaces; and

offcuts of R-plane surfaces.

91. A method of chemically mechanically polishing GaN, using a chemical mechanical polishing slurry including silica and/or alumina abrasive particles, and an acid or base, wherein the chemically mechanically polishing step is carried out to impart to the surface a root mean square (RMS) surface roughness of less than 1 nm in a 10×

10 μ

m² area thereof.

92. The method of claim 91, wherein the surface is selected from the group consisting of:

Ga-terminated surfaces of GaN in an (0001) orientation;

N-terminated surfaces of GaN in an (0001) orientation;

offcuts of Ga-terminated surfaces of GaN in an (0001) orientation;

offcuts of N-terminated surfaces of GaN in an (0001) orientation;

A-plane surfaces;

M-plane surfaces;

R-plane surfaces;

offcuts of A-plane surfaces;

offcuts of M-plane surfaces; and

offcuts of R-plane surfaces.