White-emitting LED chips and method for making same

• US 8,329,482 B2
• Filed: 04/30/2010
• Issued: 12/11/2012
• Est. Priority Date: 04/30/2010
• Status: Active Grant

• Current Assignee: Creeled Incorporated
• Original Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Inventors: Yao, Zhimin Jamie, Ibbetson, James
• Primary Examiner(s): Everhart, Caridad
• Application Number:
  US12/771,938
• Publication Number:
  US 20110266560A1
• Time in Patent Office: 956 Days
• Field of Search: 438/88, 438/28, 257/E33.056, 257/E33.001, 257/88, 257/E21.054, 257/E21.085
• US Class Current: 438/28
• CPC Class Codes: H01L 2224/16 of an individual bump connector
• CPC Class Codes: H01L 33/0093 Wafer bonding; Removal of the growth substrate
• CPC Class Codes: H01L 33/12 with a stress relaxation structure, e.g. buffer layer
• CPC Class Codes: H01L 33/22 Roughened surfaces, e.g. at the interface between epitaxial layers
• CPC Class Codes: H01L 33/486 adapted for surface mounting
• CPC Class Codes: H01L 33/50 Wavelength conversion elements
• CPC Class Codes: H01L 33/505 characterised by the shape, e.g. plate or foil

Abstract

Methods and devices for light emitting diode (LED) chips are provided. In one embodiment of a method, a pre-formed capping wafer is provided, with the capping wafer comprising a conversion material. A wire-bond free LED wafer is fabricated comprising a plurality of LEDs. The capping wafer is bonded to the LED wafer using an adhesive. The LED chips are later singulated upon completion of all final fabrication steps. The capping wafer provides a robust mechanical support for the LED chips during fabrication, which improves the strength of the chips during fabrication. Additionally, the capping wafer may comprise an integrated conversion material, which simplifies the fabrication process. In one possible embodiment for an LED chip wafer, a submount wafer is provided, along with a plurality of LEDs flip-chip mounted on the submount wafer. Additionally, a capping wafer is bonded to the LEDs using an adhesive, and the capping wafer comprises a conversion material. At least some of the light emitted from the LEDs passes through the capping wafer where at least some of the light is converted by the conversion material.

Claims

1. A method for fabricating light emitting diode (LED) chips, comprising:

pre-forming a capping wafer, said capping wafer comprising a conversion material;

fabricating a wire-bond free LED wafer comprising a plurality of LEDs;

bonding said capping wafer to said LED wafer using an adhesive such that said conversion material is adjacent said LED wafer, said capping wafer having a coefficient of thermal expansion in the range of 2-25 ppm/°

C.; and

singulating said LED chips upon the completion of all final fabrication steps.

2. The method of claim 1, wherein said capping wafer keeps said adhesive flat during curing, and further minimizes thermal stress on said LEDs.

3. The method of claim 1, wherein said capping wafer acts as a robust mechanical support for said LED chips.

4. The method of claim 1, wherein said capping wafer may be grinded down or polished prior to said singulation.

5. The method of claim 1, wherein said final fabrication steps comprise one or more of mesa etch, planarization, or metallization.

6. The method of claim 1, wherein said LEDs have a lateral geometry and comprise n- and p-type layers, and further comprise first and second contacts on said n- and p-type layers respectively.

7. The method of claim 1, wherein said capping wafer comprises multiple layers with different compositions.

8. The method of claim 1, further comprising mounting one of said LED chips to a second submount or printed circuit board (PCB).

9. The method of claim 1, further comprising flip-chip mounting said LED wafer on a surface of a submount wafer prior to said singulating.

10. The method of claim 9, wherein at least some of said singulated LED chips comprise an LED, a portion of said capping wafer, and a portion of said submount wafer.

11. The method of claim 1, wherein said capping wafer comprises a transparent layer and a coating comprising said conversion material.

12. The method of claim 11, wherein said transparent layer has a coefficient of thermal expansion (CTE) that substantially matches the CTE of said LED wafer.

13. The method of claim 11, further comprising mounting said LED chips to a submount, wherein said capping wafer comprises a transparent layer and a coating comprising said conversion material, wherein said transparent layer has a coefficient of thermal expansion (CTE) that substantially matches the CTE of said submount.

14. The method of claim 11, wherein said conversion material comprises one or more of a silicone layer with dispersed phosphor particles, a single crystal phosphor sheet, sintered phosphors, or a glass sheet filled with phosphor particles.

15. The method of claim 1, wherein said adhesive is substantially transparent and applied in a thin layer.

16. The method of claim 15, wherein said adhesive comprises silicone.

17. The method of claim 1, wherein said LED chips emit white light.

18. The method of claim 17, wherein one or more of said n- or p-type layers is shaped or textured.

19. The method of claim 1, wherein said LEDs are provided on a growth substrate.

20. The method of claim 19, further comprising removing at least a portion of said growth substrate prior to bonding said capping wafer.

21. The method of claim 19, wherein said substrate is shaped or textured.

22. A light emitting diode (LED) chip wafer, comprising:

a submount wafer;

a plurality of LEDs flip-chip mounted on said submount wafer; and

a capping wafer bonded to said LED chip wafer using an adhesive, said capping wafer comprising a conversion material, wherein said conversion material is adjacent said LED chip wafer, said capping wafer further comprising a material acting as a robust mechanical support for said LEDs, said capping wafer having a coefficient of thermal expansion in the range of 2-25 ppm/°

C.;

wherein at least some of the light emitted from said LEDs passes through said capping wafer where at least some of said light is converted by said conversion material;

wherein said LEDs are capable of being singulated.

23. The LED chip wafer of claim 22, wherein the coefficient of thermal expansion for said robust mechanical support material is substantially the same as the CTE for the material comprising the LEDs in said LED chip wafer.

24. The LED chip wafer of claim 22, wherein the coefficient of thermal expansion for said robust mechanical support material is substantially the same as the CTE of the material comprising said submount wafer.

25. The LED chip wafer of claim 22, wherein there is less than a 40% difference in the coefficient of thermal expansion for said robust mechanical support material compared to the CTE of the material comprising the LEDs in said LED chip wafer.

26. The LED chip wafer of claim 22, wherein there is less than a 40% difference in the coefficient of thermal expansion for said robust mechanical support material compared to the CTE of the material comprising the submount wafer.

27. The LED chip wafer of claim 22, wherein there is less than a 30% difference in the coefficient of thermal expansion for said robust mechanical support material compared to the CTE of the material comprising the LEDs in said LED chip wafer.

28. The LED chip wafer of claim 22, wherein there is less than a 30% difference in the coefficient of thermal expansion for said robust mechanical support material compared to the CTE of the material comprising the submount wafer.

29. The LED chip wafer of claim 22, wherein at least some of said LEDs have lateral geometry.

30. The LED chip wafer of claim 22, wherein said submount wafer is capable of being separated into LED chips.

31. The LED chip wafer of claim 22, wherein said capping wafer has a uniform thickness above said LEDs.

32. The LED chip wafer of claim 22, wherein said LEDs are made of materials from the Group-III nitride material system.

33. The LED chip wafer of claim 22, wherein said LEDs are interconnected in an LED array.

34. The LED chip wafer of claim 22, capable of emitting white light from said LEDs and capping wafer.

35. The LED chip wafer of claim 22, wherein said adhesive is substantially transparent, applied in a thin layer, and comprises silicone.

36. The LED chip wafer of claim 22, wherein the thickness of the conversion material can be individually tailored at each LED at the wafer level either before or after said capping wafer and said LED wafer are bonded together.

37. The LED chip wafer of claim 36, wherein said conversion material comprises phosphor.

38. The LED chip wafer of claim 22, wherein said wherein said robust support material comprises a transparent material.

39. The LED chip wafer of claim 38, wherein said transparent material comprises one or more of glass, SiC, sapphire, GaN, or ZnO, and said conversion material comprises one or more of a silicone layer with dispersed phosphor particles, a single crystal phosphor sheet, sintered phosphors, or a glass sheet filled with phosphor particles.

40. A light emitting diode (LED) chip, comprising:

a wire-bond free LED;

a capping wafer bonded to said LED using an adhesive, said capping wafer serving as a mechanical support for said LED chip; and

a conversion material integrated in said capping wafer, said conversion material adjacent said LED and converting at least some of the light emitted from said LED, said capping wafer having a coefficient of thermal expansion in the range of 2-25 ppm/°

C.

41. The LED chip of claim 40, wherein said capping wafer is continuous over the top surface of said LED and has a substantially uniform thickness.

42. The LED chip of claim 40, emitting a white light combination of LED light and light from said conversion material.

43. The LED chip of claim 40, further comprising a submount, said LED flip-chip mounted on said submount.

44. The LED chip of claim 40, wherein said capping wafer comprises:

a transparent portion; and

a layer comprising said conversion material;

wherein said transparent portion comprises one or more of glass, SiC, sapphire, GaN, or ZnO, and said conversion material comprises one or more of a silicone layer with dispersed phosphor particles, a single crystal phosphor sheet, sintered phosphors, or a glass sheet filled with phosphor particles.

45. The LED chip of claim 40, wherein said adhesive comprises silicone.