Wafer level phosphor coating technique for warm light emitting diodes

• US 20090057690A1
• Filed: 10/13/2008
• Published: 03/05/2009
• Est. Priority Date: 01/22/2007
• Status: Active Grant

• Current Assignee: Creeled Incorporated
• Original Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Inventors: Chakraborty, Arpan
• Granted Patent: US 8,232,564 B2
• Time in Patent Office: Days
• US Class Current: 257/88
• CPC Class Codes: H01L 2224/16 of an individual bump connector
• CPC Class Codes: H01L 23/3114 the device being a chip scale package, e.g. CSP
• CPC Class Codes: H01L 2933/0041 relating to wavelength conversion elements
• CPC Class Codes: H01L 33/38 with a particular shape
• CPC Class Codes: H01L 33/44 characterised by the coatings, e.g. passivation layer or anti-reflective coating
• CPC Class Codes: H01L 33/504 Elements with two or more wavelength conversion materials
• CPC Class Codes: H01L 33/62 Arrangements for conducting electric current to or from the semiconductor body, e.g. lead-frames, wire-bonds or solder balls

Abstract

Methods for wafer level fabricating of light emitting diode (LED) chips are disclosed with one embodiment of a method according to the present invention comprising providing a plurality of LEDs and then coating of the LEDs with a layer of first conversion material so that at least some light from the LEDs passes through the first conversion material. The light is converted to different wavelengths of light having a first conversion material emission spectrum. The LEDs are then coated with a layer of second conversion material arranged on the first layer of conversion. The second conversion material has a wavelength excitation spectrum, and at least some light from the LEDs passes through the second conversion material and is converted. The first conversion material emission spectrum does not substantially overlap with the second conversion material excitation spectrum. Methods according to the present invention can also be used in wafer level fabrication of LED chips and LED packages with pedestals for electrically contacting the LEDs through the conversion coatings.

Claims

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

providing a plurality of LEDs;

coating said LEDs with a first conversion layer having first conversion material with a first conversion material emission spectrum;

coating said LEDs with a second conversion layer arranged on said first conversion layer, said second conversion material having a conversion material different from said first conversion material and having a second conversion material wavelength excitation spectrum; and

wherein said first conversion material emission spectrum does not substantially overlap with said second conversion material excitation spectrum.

2. The method of claim 1, wherein at least some light from said LEDs passes through said first conversion material and is converted to a different wavelength.

3. The method of claim 1, wherein at least some light from said LEDs passes through said second conversion material and is converted to a different wavelength.

4. The method of claim 1, wherein said first and second conversion materials comprise phosphors.

5. The method of claim 1, wherein said first conversion material is a red phosphor and said second conversion material is a yellow phosphor.

6. The method of claim 1, wherein each of said LED chips emits a combination of LED light and first and second conversion material light.

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

8. The method of claim 1, wherein said LEDs emit blue light, said first conversion absorbs at least some of said blue LED light and emits red light and said second conversion material absorbs at least some of said blue light and emits yellow light, said LED chips emitting a white light combination of said LED light and conversion material light.

9. The method of claim 1, further comprising removal of said first conversion layer or said second conversion layer to change the emission characteristics of said LED chips to within a range of target emission characteristics.

10. The method of claim 9, wherein the amount of conversion material to be removed is determined by the emission characteristics of said LED chips relative to target emission characteristics.

11. The method of claim 1, further comprising measuring the emission characteristics of at least some of said LEDs.

12. The method of claim 1, wherein said plurality of LEDs are provided on a wafer and said LED chips are formed from said wafer.

13. The method of claim 12, further comprising singulating said LEDs from said wafer as individual LED chips or groups of LED chips.

14. The method of claim 1, further comprising planarizing said layer of first conversion material.

15. The method of claim 1, further comprising planarizing said layer of second conversion material.

16. The method of claim 1, further comprising forming a spacer layer between said LEDs and said layer of first conversion layer.

17. The method of claim 1, further comprising coating said LEDs with a layer of third conversion layer having a conversion material with a third conversion material excitation spectrum, wherein light from said LEDs passes through said third conversion material and is converted to a different wavelength.

18. The method of claim 15, wherein said second conversion layer has a second conversion layer emission spectrum, wherein said third conversion material excitation spectrum does not substantially overlap with said first and second conversion material emission spectrums.

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

providing a plurality of LEDs;

depositing a pedestal on at least one of said LEDs, said pedestal in electrical contact with its one of said LEDs;

forming a first conversion layer on said LEDs;

planarizing said layer of first conversion material leaving at least some of said first conversion layer on said LEDs while exposing said pedestal;

forming a second conversion layer on said first conversion layer, said second conversion layer being different from said first conversion layer; and

planarizing said layer of second conversion layer leaving at least some of said second conversion layer on said LEDs while exposing at least some of said pedestal.

20. The method of claim 19, wherein at least some light from said LEDs passes through said first conversion layer and is converted to a different wavelength.

21. The method of claim 19, wherein at least some light from said LEDs passes through said second conversion layer and converted to a different wavelength.

22. The method of claim 19, further comprising micromachining said layer of first conversion layer to remove a portion of said on at least some of said LEDs without removing said pedestals.

23. The method of claim 22, wherein said second conversion layer is in said micromachined portion of said first layer of conversion material.

24. The method of claim 19, wherein said LED light is converted by said first conversion layer into an emission spectrum, and said second conversion layer has an excitation spectrum, wherein said emission spectrum does not substantially overlap with said excitation spectrum.

25. The method of claim 19, wherein said LED light is converted by said first conversion layer into an emission spectrum, and said second conversion layer has an excitation spectrum, wherein said emission spectrum does not overlap with said excitation spectrum.

26. The method of claim 19, further comprising curing said layers of first and second conversion materials prior to planarizing.

27. The method of claim 19, wherein said first and second conversion layers comprise phosphors.

28. The method of claim 19, wherein said first conversion layer comprises a red phosphor and said second conversion layer comprises a yellow phosphor.

29. The method of claim 19, wherein each of said LED chips emits a combination of LED light and first and second conversion layer light.

30. The method of claim 19, wherein said LED chips emit white light.

31. The method of claim 19, further comprising removal of said first conversion material or said second conversion material to change the emission characteristics of said LED chips to within a range of target emission characteristics.

32. The method of claim 19, wherein said plurality of LEDs are provided on a wafer.

33. The method of claim 19, further comprising forming a spacer layer between said LEDs and said layer of first conversion layer.

34. The method of claim 19, further comprising singulating said LED chips.

35. The method of claim 19, wherein said pedestals are formed using stud bumping.

36. The method of claim 19, further comprising packaging said LED chips.

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

a plurality of LEDs on a wafer;

a first conversion layer on at least some of said LEDs, said first conversion layer having a first conversion material with a first emission spectrum;

a second conversion layer having a second conversion material with a second excitation spectrum, and arranged on said first conversion layer; and

wherein said first emission spectrum does not substantially overlap with the said second excitation spectrum.

38. The LED chip wafer of claim 37, wherein second conversion material is different from said first conversion material.

39. The LED chip wafer of claim 37, further comprising a plurality of pedestals, each of which is in electrical contact with one of said LEDs, at least some of said pedestals extending through said first and second conversion layers and exposed at the top surface of said layers.

40. The LED chip wafer of claim 39, wherein electrical contact is made to said LED chips through said pedestals.

41. The LED chip wafer of claim 37, wherein said first and second conversion materials comprise phosphors.

42. The LED chip wafer of claim 37, wherein said first conversion material is a red phosphor and said second conversion material is a yellow phosphor.

43. The LED chip wafer of claim 37, wherein each of said LED chips emits a combination of LED light and first and second conversion material light.

44. The LED chip wafer of claim 37, wherein said LED chips emit white light.

45. The LED chip wafer of claim 37, wherein the output of said LED chips is altered by removal of said first conversion material or said second conversion material to change the emission characteristics of said LED chips to within a range of target emission characteristics.

46. The LED chip wafer of claim 37, wherein said second conversion material comprises phosphor particles having a size in relation to said wavelength of light emitted by said LED to substantially eliminate backscattering of light from said second conversion material.

47. The LED chip wafer of claim 46, wherein said LED emits blue light and said phosphor particles have a diameter of greater than 10 micrometers.

48. The LED chip wafer of claim 37, further comprising a spacer layer between said LEDs and said first conversion layer.

49. The LED chip wafer of claim 37, further comprising a third conversion layer having a conversion material with a third excitation spectrum, said third conversion layer arranged on said second layer of conversion material, wherein at least some light from said LEDs passes through said third conversion material and is converted.

50. The LED chip wafer of claim 49, wherein said second conversion material has a second emission spectrum, wherein said third conversion excitation spectrum does not substantially overlap with said first and second emission spectrums.

51. The LED chip wafer of claim 49, wherein said third conversion material comprises phosphor particles having a size in relation to the wavelength of light emitted by said LED to substantially eliminate backscattering of light from said third conversion material.

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

an LED;

a pedestal in electrical contact with said LED;

a layer of first conversion material on said LED; and

a layer of second conversion material on said coating of first conversion material, said second conversion material being different than said first conversion material, wherein said pedestal is configured to provide electrical connection to said LED.

53. The LED chip of claim 52, wherein said pedestal extends through and to the surface of said coatings.

54. The LED chip of claim 52, wherein said LED is on a substrate.

55. The LED chip of claim 52, wherein LED light is converted by said first conversion material into an emission spectrum, and said second conversion material has an excitation spectrum, wherein said emission spectrum does not substantially overlap with said excitation spectrum.

56. The LED chip of claim 52, wherein said LED light is converted by said first conversion material into an emission spectrum, and said second conversion material has an excitation spectrum, wherein said emission spectrum does not overlap with said excitation spectrum.

57. The LED chip of claim 52, wherein electrical contact is made to said LED chips through said pedestals.

58. The LED chip of claim 52, wherein said first and second conversion materials comprise phosphors.

59. The LED chip of claim 52, wherein said first conversion material is a red phosphor and said second conversion material is a yellow phosphor.

60. The LED chip of claim 52, wherein each of said LED chips emits a combination of LED light and first and second conversion material light.

61. The LED chip of claim 52, wherein said LED chips emit white light.

62. The LED chip of claim 52 wherein said pedestal comprises one or more stud bumps.

63. The LED chip of claim 52, further comprising a spacer layer between said LEDs and said layer of first conversion material.

64. A light emitting diode (LED) package comprising:

an LED and a pedestal in electrical contact with said LED;

a coating of first conversion material on said LED;

a coating of second conversion material on said coating of first conversion material;

a package lead in electrical connection with said pedestal; and

encapsulation over said LED chip and electrical connection.

65. An LED package of claim 64, wherein said encapsulation comprises a hermetically sealed cover over said LED chip.

66. A method for fabricating LED chips, comprising:

flip-chip bonding a plurality of LEDs on a carrier substrate;

depositing a conductive pedestal on each of the LEDs;

coating said LEDs with a layer of first conversion material so that at least some light from said LEDs passes through said first conversion material and is converted to a different wavelength;

planarizing said layer of first conversion material;

coating said LEDs with a layer of second conversion material arranged different from said first conversion material, said second conversion material being different from said first conversion material, wherein at least some light from said LEDs passes through said second conversion material and converted; and

planarizing said layer of second conversion material.

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

a plurality of LEDs on a wafer;

a plurality of pedestals each of which is in electrical contact with one of said LEDs;

a layer of first conversion material on at least some of said LEDs; and

a layer of second conversion material on said coating of first conversion material, said second conversion material being different than said first conversion material.

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

providing a plurality of LEDs on a wafer;

forming a first conversion layer on at least some of said LEDs, said first conversion layer having a first conversion material;

singulating an LED chip from said wafer;

forming a second conversion layer on said LED chip, said second conversion layer having a second conversion material complimenting said first conversion material so that said LED chip emits a combination of LED light, first conversion layer light, and second conversion material light at a desired emission.

69. The method of claim 68, wherein said first conversion material has a first conversion material emission spectrum and said second conversion material has a second conversion material excitation spectrum, wherein said first conversion material emission spectrum does not substantially overlap with said second conversion material excitation spectrum.