Package-integrated thin film LED

• US 20060091409A1
• Filed: 10/28/2004
• Published: 05/04/2006
• Est. Priority Date: 10/28/2004
• Status: Active Grant

• Current Assignee: Lumileds LLC (Apollo Global Management, Inc.)
• Original Assignee: Lumileds Lighting US LLC (Apollo Global Management, Inc.)
• Inventors: Krames, Michael R., Martin, Paul S., Epler, John
• Granted Patent: US 7,256,483 B2
• Time in Patent Office: Days
• US Class Current: 257/95
• CPC Class Codes: H01L 2224/32225 the item being non-metallic, e.g. insulating substrate with or without metallisation
• CPC Class Codes: H01L 2224/45014 Ribbon connectors, e.g. rectangular cross-section
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/48227 connecting the wire to a bond pad of the item
• CPC Class Codes: H01L 2224/48464 the other connecting portion not on the bonding area also being a ball bond, i.e. ball-to-ball
• CPC Class Codes: H01L 2224/73265 Layer and wire connectors
• CPC Class Codes: H01L 2224/92247 the second connecting process involving a wire connector
• CPC Class Codes: H01L 24/73 Means for bonding being of different types provided for in two or more of groups H01L24/10, H01L24/18, H01L24/26, H01L24/34, H01L24/42, H01L24/50, H01L24/63, H01L24/71
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/00012 Relevant to the scope of the group, the symbol of which is combined with the symbol of this group
• CPC Class Codes: H01L 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H01L 2924/206 Length ranges
• CPC Class Codes: H01L 33/0093 Wafer bonding; Removal of the growth substrate
• CPC Class Codes: H01L 33/22 Roughened surfaces, e.g. at the interface between epitaxial layers
• CPC Class Codes: H01L 33/32 containing nitrogen
• CPC Class Codes: H01L 33/48 characterised by the semiconductor body packages
• CPC Class Codes: H01L 33/486 adapted for surface mounting

Abstract

LED epitaxial layers (n-type, p-type, and active layers) are grown on a substrate. For each die, the n and p layers are electrically bonded to a package substrate that extends beyond the boundaries of the LED die such that the LED layers are between the package substrate and the growth substrate. The package substrate provides electrical contacts and conductors leading to solderable package connections. The growth substrate is then removed. Because the delicate LED layers were bonded to the package substrate while attached to the growth substrate, no intermediate support substrate for the LED layers is needed. The relatively thick LED epitaxial layer that was adjacent the removed growth substrate is then thinned and its top surface processed to incorporate light extraction features. There is very little absorption of light by the thinned epitaxial layer, there is high thermal conductivity to the package because the LED layers are directly bonded to the package substrate without any support substrate therebetween, and there is little electrical resistance between the package and the LED layers so efficiency (light output vs. power input) is high. The light extraction features of the LED layer further improves efficiency.

Claims

1. A light emitting device comprising:

a light emitting diode (LED) portion comprising;

a first epitaxial layer of a first conductivity type formed on a growth substrate, the growth substrate having been removed from the LED portion;

a second epitaxial layer of a second conductivity type formed on the growth substrate;

an active layer disposed between the first and second epitaxial layers;

a primary emission surface on a first side of the first epitaxial layer substantially parallel to the active layer,

a package substrate on which the LED portion is mounted; and

a metal interface, disposed between the package substrate and the second epitaxial layer, electrically connecting a conductor on the package substrate to the second epitaxial layer with no support substrate therebetween;

wherein a nearest distance between the primary emission surface and a portion of the package substrate is not more than 50 microns, and wherein a lateral extent of the package substrate exceeds that of the LED portion.

2. The device of claim 1 further comprising a metal layer deposited over the second epitaxial layer, wherein the metal interface comprises a solder bond between the metal layer and the conductor on the package.

3. The device of claim 1 further comprising a metal layer deposited over the second epitaxial layer, wherein the metal interface comprises an ultrasonic weld of the metal layer to the conductor on the package.

4. The device of claim 1 further comprising a metal layer deposited over the second epitaxial layer, wherein the metal interface comprises a thermocompression bond of the metal layer to the conductor on the package.

5. The device of claim 1 further comprising a metal layer deposited over the second epitaxial layer, wherein the metal interface comprises an interdiffusion bond of the metal layer to the conductor on the package.

6. The device of claim 1 further comprising an electrical connector between the first epitaxial layer and a contact pad on the package substrate.

7. The device of claim 6 wherein the electrical connector is a wire.

8. The device of claim 7 wherein the electrical connector is a wire ribbon.

9. The device of claim 6 wherein the electrical connector is a metal bridge.

10. The device of claim 6 wherein the LED is a flip-chip, and wherein the electrical connector comprises a metal bond bonding the first epitaxial layer to a contact pad on the package substrate.

11. The device of claim 1 wherein the LED is a flip-chip, and the metal interface is formed in a pattern.

12. The device of claim 1 wherein the primary emission surface incorporates a light extraction feature.

13. The device of claim 1 wherein the LED is formed of gallium-nitride or gallium phosphide based materials.

14. The device of claim 1 further comprising a plurality of LEDs on the package substrate, each LED having its growth substrate removed and having no support substrate other than the package substrate.

15. The device of claim 1 further comprising a plurality of LEDs on the package substrate, each LED having its growth substrate removed and having no support substrate other than the package substrate, the plurality of LEDs being arranged in groups of arrays.

16. The device of claim 1 wherein the first epitaxial layer comprises a plurality of epitaxial layers of the first conductivity type, and wherein the second epitaxial layer comprises a plurality of epitaxial layers of the second conductivity type.

17. The device of claim 1 further comprising a phosphor over the LED portion.

18. The device of claim 1 further comprising an optical element over the LIED portion.

19. The device of claim 1 wherein the package substrate is thermally conductive to act as a heat sink for the LED portion.

20. The device of claim 1 wherein the LED layers have a thickness less than 3 microns.

21. The device of claim 1 wherein the LED layers have a thickness less than 10 microns.

22. The device of claim 1 further comprising a housing surrounding the LED portion and package substrate, the housing containing metal leads extending from the housing and electrically coupled to the package substrate.

23. The device of claim 1 wherein the primary emission surface has light extraction features formed in it.

24. The device of claim 1 wherein the first epitaxial layer has been thinned after the growth substrate has been removed and after the LED portion has been mounted on the package substrate.

49. The device of claim 1 further comprising an underfill disposed between the LED portion and the package substrate.

25. A method comprising:

growing light emitting diode (LED) layers on a growth substrate, the LED layers comprising a first epitaxial layer of a first conductivity type, a second epitaxial layer of a second conductivity type formed on the growth substrate, and an active layer disposed between the first and second epitaxial layers, wherein a primary emission surface on a first side of the first epitaxial layer is substantially parallel to the active layer, the LED layers forming at least one individual LED;

providing a package substrate wherein a lateral extent of the package substrate exceeds that of an individual LED, the package substrate comprising a support surface having one or more electrical contact pads thereon for electrical connection to the first and second epitaxial layers, the contact pads being electrically connected to metal leads for connection to package terminals;

placing the LED layers attached to the growth substrate on the package substrate such the second epitaxial layer is facing a first contact pad on the package substrate;

bonding the second epitaxial layer to the first contact pad using a metal interface disposed between the package substrate and the second epitaxial layer, wherein a nearest distance between tire primary emission surface and a portion of the package substrate is not more than 50 microns;

removing the growth substrate; and

further processing the LED layers after the growth substrate has been removed.

26. The method of claim 25 wherein the growth substrate is sapphire, and removing the growth substrate comprises performing a laser liftoff process.

27. The method of claim 25 wherein the growth substrate comprises silicon, and removing the growth substrate comprises performing an etching process.

28. The method of claim 25 wherein the LED layers comprise AlInGaP, and the growth substrate comprises GaAs or Ge.

29. The method of claim 25 further comprising mounting the LED portion and package substrate in a housing surrounding the LED portion and package substrate, and electrically connecting metal leads extending from the housing to contact areas on the package substrate.

30. The method of claim 25 wherein placing the LED layers comprises placing a plurality of LEDs on the package substrate.

31. The method of claim 25 further comprising:

depositing a protective layer over the package substrate after the LED layers have been placed on the package substrate to protect the package substrate; and

etching a portion of the first epitaxial layer.

32. The method of claim 31 wherein etching a portion of the first epitaxial layer comprising etching at least 50% of the thickness of the first epitaxial layer.

33. The method of claim 25 further comprising providing an electrical connector between the first epitaxial layer and a contact pad on the package substrate.

34. The method of claim 33 wherein the electrical connector is a wire.

35. The method of claim 33 wherein the electrical connector is a metal bridge.

36. The method of claim 33 wherein the LED is a flip-chip, wherein providing the electrical connector comprises bonding the first epitaxial layer to a contact pad on the package substrate.

37. The method of claim 25 further comprising dicing the package substrate after the growth substrate has been removed, each package substrate die having one or more LEDs mounted on it.

38. The method of claim 25 wherein growing LED layers comprises growing gallium-nitride based LED layers.

39. The method of claim 25 further comprising dicing the LED layers and growth substrate prior to placing the LED layers on the package substrate.

40. The method of claim 25 wherein placing the LED layers on the package substrate comprises placing the LED layers on the package substrate prior to dicing the LED layers and the growth substrate, wherein removing the growth substrate comprises removing the entire growth substrate intact, and further comprising dicing the package substrate after removing the growth substrate.

41. The method of claim 25 wherein the first epitaxial layer comprises a plurality of epitaxial layers of the first conductivity type, and wherein the second epitaxial layer comprises a plurality of epitaxial layers of the second conductivity type.

42. The method of claim 25 further comprising etching the first epitaxial layer after removing the growth substrate, such that the LED layers have a thickness less than 3 microns.

43. The method of claim 25 further comprising etching the first epitaxial layer after removing the growth substrate, such that the LED layers have a thickness less than 10 microns.

44. The method of claim 25 wherein further processing the LED layers comprises forming light extraction features in the primary emission surface.

45. The method of claim 44 wherein forming light extraction features consists of roughening the primary emission surface, patterning the primary emission surface, dimpling the primary emission surface, or forming a photonic crystal.

46. The method of claim 25 wherein further processing the LED layers comprises thinning the first epitaxial layer.

47. The method of claim 25 further comprising providing an underfill between the LED layers and the package substrate.

48. The method of claim 47 wherein said providing an underfill occurs prior to removing the growth substrate.

50. A method comprising:

providing a growth substrate comprising a first layer connected to a second layer;

growing light emitting diode (LED) layers on the first layer of the growth substrate, the LED layers comprising a first epitaxial layer of a first conductivity type, a second epitaxial layer of a second conductivity type, and an active layer disposed between the first and second epitaxial layers, and

bonding the LED layers to a package substrate; and

removing at least a portion of the growth substrate by wet etching.

51. The method of claim 50 wherein the first layer is SiC.

52. The method of claim 50 wherein the second layer is an insulator.

53. The method of claim 52 wherein removing at least a portion of the growth substrate by wet etching comprises etching away the second layer.

54. The method of claim 53 further comprising after etching away the second layer, removing off the first layer.

55. The method of claim 50 wherein a nearest distance between a primary emission surface of the LED layers and a surface of the package substrate is not more than 50 microns, and wherein a lateral extent of the package substrate exceeds that of the LED layers.

56. The method of claim 50 wherein a lateral extent of the package substrate exceeds that of the LED layers.