Method of Forming Three-Dimensional Features on Light Emitting Diodes for Improved Light Extraction

• US 20070037307A1
• Filed: 07/31/2006
• Published: 02/15/2007
• Est. Priority Date: 04/01/2004
• Status: Active Grant

• Current Assignee: CREE Led Incorporated (Smart Global Holdings Incorporated)
• Original Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Inventors: Donofrio, Matthew
• Granted Patent: US 7,384,809 B2
• Time in Patent Office: Days
• US Class Current: 438/42
• CPC Class Codes: B23K 2101/40 Semiconductor devices
• CPC Class Codes: B23K 2103/50 Inorganic material, e.g. metals, not provided for in B23K2103/02 – B23K2103/26
• CPC Class Codes: B23K 2103/52 Ceramics
• CPC Class Codes: B23K 26/066 by using masks
• CPC Class Codes: B23K 26/40 taking account of the properties of the material involved
• CPC Class Codes: H01L 33/0095 Post-treatment of devices, e.g. annealing, recrystallisation or short-circuit elimination
• CPC Class Codes: H01L 33/20 with a particular shape, e.g. curved or truncated substrate
• CPC Class Codes: H01L 33/32 containing nitrogen
• CPC Class Codes: Y10S 438/94 Laser ablative material removal

Abstract

A method is disclosed for obtaining a high-resolution lenticular pattern on the surface of a light emitting diode. The method comprises imprinting a patterned sacrificial layer of etchable material that is positioned on a semiconductor surface that is in turn adjacent a light emitting active region, and thereafter etching the imprinted sacrificial layer and the underlying semiconductor to transfer an imprinted pattern into the semiconductor layer adjacent the light emitting active region.

Claims

1. A method of obtaining a lenticular pattern on the surface of a light emitting diode, the method comprising imprinting a pattern into a layer of etchable material that is positioned on a semiconductor surface that is in turn adjacent a light emitting active region.

2. A method according to claim 1 further comprising etching the imprinted layer and the underlying semiconductor to transfer an imprinted pattern into the semiconductor layer adjacent the light emitting active region.

3. A method according to claim 1 comprising imprinting a patterned sacrificial layer on a silicon carbide surface.

4. A method according to claim 1 comprising imprinting a patterned sacrificial layer on a sapphire surface.

5. A method according to claim 1 comprising imprinting a patterned sacrificial layer on a Group III nitride surface.

6. A method according to claim 1 comprising imprinting a patterned sacrificial layer on a gallium nitride surface.

7. A method according to claim 1 comprising imprinting a patterned sacrificial layer of photoresist.

8. A method according to claim 7 comprising forming the etchable layer prior to the imprinting step by adding an epoxy-based photoresist to a silicon carbide surface.

9. A method according to claim 8 comprising soft baking the photoresist to evaporate solvent and densify the photoresist prior to the imprinting step.

10. A method according to claim 7 wherein the imprinting step comprises heating the semiconductor to a temperature sufficient to soften the photoresist but less than a temperature at which the photoresist will flow and thereafter pressing an embossing stamp into the heated photoresist.

11. A method according to claim 10 wherein the step of pressing the embossing stamp comprises pressing a soft stamp.

12. A method according to claim 10 wherein the imprinting step comprises stamping the photoresist with a negative image of the features desired in the photoresist.

13. A method according to claim 12 comprising cooling the stamped photoresist and thereafter separating the embossing stamp from the photoresist and the semiconductor surface.

14. A method according to claim 13 comprising cross-linking the imprinted photoresist and thereafter baking the photoresist below its glass transition temperature.

15. A method according to claim 14 comprising cross-linking the imprinted photoresist by exposure to ultraviolet light.

16. A method according to claim 1 comprising imprinting a pattern into an etchable material selected from the group consisting of thermosetting resins, other thermally curable resins and two-part epoxies that react upon mixing.

17. A method according to claim 14 further comprising baking the embossed exposed photoresist above the glass transition temperature of the photoresist after the photoresist is sufficiently cross-linked to remain dimensionally stable at higher temperatures.

18. A method according to claim 2 comprising etching the imprinted layer to completely sacrifice the imprinted layer and produce the resulting features in the semiconductor.

19. A method according to claim 2 comprising etching the imprinted layer in an inductively coupled plasma.

20. A method according to claim 2 comprising reactive ion etching the imprinted layer.

21. A method according to claim 2 comprising embossing the etchable layer to create an aspect ratio in the resulting embossed features that produces a desired aspect ratio in the semiconductor surface that is based upon the etch selectivity between the photoresist and the semiconductor material.

22. A method according to claim 2 wherein the etching step comprises transferring features into the semiconductor layer with footprint dimensions that are smaller than 10 microns.

23. A method according to claim 2 wherein the etching step comprises transferring features into the semiconductor layer with footprint dimensions that are smaller than 6 microns.

24. A method according to claim 2 wherein the etching step comprises transferring features into the semiconductor layer with footprint dimensions that are smaller than 1 micron.

25. A method according to claim 8 comprising minimizing the thickness of the photoresist between the imprinted pattern and the semiconductor surface to thereby increase the resolution of the resulting features in the etched semiconductor.

26. A method according to claim 8 comprising substantially eliminating the thickness of the photoresist between the imprinted pattern and the semiconductor surface to thereby increase the resolution of the resulting features in the etched semiconductor.

27. A method according to claim 2 further comprising the step of growing an epitaxial layer on the imprinted patterned semiconductor layer.

28. A method according to claim 27 comprising growing a gallium nitride layer on patterned sapphire.

29. An LED precursor structure comprising:

at least one Group III nitride active layer;

a photoresist layer on said Group III nitride-layer; and

an embossing stamp pressed into said photoresist layer.

30. An LED precursor according to claim 29 wherein said photoresist layer is heated to a temperature sufficient to soften the photoresist but below the temperature at which the photoresist would lose structural integrity.

31. An LED precursor according to claim 29 heated to a temperature of between about 50 and 100°

C.

32. An LED precursor according to claim 29 further comprising a conductive substrate supporting said Group III nitride layer.

33. A method of obtaining a high resolution lenticular pattern on a wide bandgap light emitting diode;

the method comprising;

adding a photoresist layer to the surface of a semiconductor layer which in turn is on at least one Group III nitride active layer which in turn is on a submounting structure;

heating the photoresist layer to a temperature sufficient to internally soften the photoresist but less than the temperature at which the photoresist would lose its self resolution structure;

imprinting the heated photoresist layer with an embossing stamp that carries the negative image of the pattern desired for the photoresist;

removing the stamp from the photoresist to leave behind an embossed patterned photoresist;

curing the patterned photoresist; and

removing the entire patterned photoresist layer in a plasma etch along with corresponding portions of the underlying semiconductor layer to produce a lenticular pattern in the semiconductor layer corresponding to the embossing stamp, the embossed photoresist, and the etching ratio between the photoresist and the semiconductor in the plasma etch.

34. A method according to claim 33 comprising imprinting the photoresist layer with a soft stamp.

35. A method according to claim 33 comprising cooling the photoresist between the imprinting and removing steps.

36. A method according to claim 33 comprising removing the photoresist layer and underlying semiconductor with an inductively coupled plasma etch.

37. A method according to claim 33 comprising removing the photoresist layer and underlying semiconductor with reactive ion etch.

38. A method according to claim 33 wherein the step of curing the patterned photoresist comprises exposing the photoresist to a frequency of light that initiates the cure and baking the photoresist at a temperature that substantially completes the cure.

39. A method of obtaining a lenticular surface on a light emitting diode precursor, the method comprising:

adding a planarizing material to a plurality of silicon carbide mesas and adjacent trenches on a common Group III nitride layer which in turn is on a submounting structure;

removing the planarizing material from the surface of the silicon carbide mesas while permitting the material to remain in the trenches between adjacent silicon carbide mesas and to thereby present a common planar surface of silicon carbide and planarizing material;

adding a photoresist layer to the common planar surface;

imprinting the photoresist with an embossing stamp;

removing the embossing stamp from the imprinted photoresist; and

etching the photoresist to completely remove the photoresist, the planarizing material and portions of the underlying silicon carbide to produce a lenticular pattern in the silicon carbide defined by the embossed photoresist and the etch ratio between the photoresist and the silicon carbide in the etching material.

40. A method according to claim 39 wherein the step of adding the planarizing material comprises adding a settable, embossable and curable polymer resin.

41. A method according to claim 39 wherein the step of adding the planarizing material comprises adding another photoresist.

42. A method according to claim 39 wherein the step of removing the planarizing material comprises polishing the material.

43. An LED comprising:

a conductive substrate;

at least one light-emitting active layer on said substrate; and

a patterned semiconductor lenticular surface on said active layer opposite said substrate with no more than 25 microns of non-lenticular material between said patterned lenticular surface and said active layer.

44. An LED according to claim 43 wherein said lenticular surface comprises a plurality of lenticular features that are smaller than 10 microns in their individual footprints.

45. An LED according to claim 43 wherein said lenticular surface comprises a plurality of substantially identical lenticular features.

46. An LED according to claim 43 wherein said lenticular surface comprises a plurality of lenticular features that are smaller than 6 microns in their individual footprints.

47. An LED according to claim 43 wherein said active layer comprises a Group III nitride.

48. An LED according to claim 47 wherein said lenticular surface comprises silicon carbide.

49. A method of obtaining a lenticular pattern on the surface of a light emitting diode, the method comprising:

imprinting a patterned sacrificial layer of etchable material that is positioned on the surface of a semiconductor structure that includes a light emitting active region; and

thereafter etching the imprinted sacrificial layer and the underlying semiconductor to transfer the imprinted pattern.

50. A method according to claim 49 comprising imprinting the sacrificial layer on a Group III nitride surface to produce a patterned Group III nitride surface.

51. A method according to claim 49 comprising forming the sacrificial layer prior to the imprinting step by adding an epoxy-based photoresist to a silicon carbide surface.

52. A method according to claim 49 comprising etching the imprinted sacrificial layer to completely sacrifice the imprinted layer and produce the resulting features in the semiconductor.

53. A method according to claim 49 comprising embossing the sacrificial layer to create an aspect ratio in the resulting embossed features that produces a desired aspect ratio in the semiconductor surface that is based upon the etch selectivity between the photoresist and the semiconductor material.

54. A method of obtaining a lenticular pattern on the surface of a light emitting diode, the method comprising:

imprinting a pattern into a layer of photoresist that is positioned on a semiconductor surface that is in turn adjacent a light emitting active region;

masking the photoresist with a complementary pattern;

exposing and developing the photoresist; and

thereafter etching the imprinted developed photoresist and the underlying semiconductor to transfer the imprinted and complementary patterns into the semiconductor layer adjacent the light emitting active region.

55. A method according to claim 54 comprising:

imprinting the photoresist with an embossing stamp; and

masking and exposing the photoresist with the stamp in place.

56. A method according to claim 54 comprising:

imprinting the photoresist with an embossing stamp;

removing the stamp from the photoresist; and

thereafter masking and exposing the photoresist.

57. A method according to claim 54 wherein the imprinting step comprises heating the semiconductor to a temperature sufficient to soften the photoresist but less than a temperature at which the photoresist will flow and thereafter pressing an embossing stamp into the heated photoresist.

58. A method according to claim 54 comprising etching the imprinted layer to completely sacrifice the imprinted layer and produce the resulting features in the semiconductor.

59. A method according to claim 54 comprising embossing the etchable layer to create an aspect ratio in the resulting embossed features that produces a desired aspect ratio in the semiconductor surface that is based upon the etch selectivity between the photoresist and the semiconductor material.

60. A method according to claim 54 wherein the etching step comprises transferring features into the semiconductor layer with footprint dimensions that are smaller than 10 microns.

61. A method according to claim 54 wherein the etching step comprises transferring features into the semiconductor layer with footprint dimensions that are smaller than 1 micron.

62. A method according to claim 54 comprising minimizing the thickness of the photoresist between the imprinted pattern and the semiconductor surface to thereby increase the resolution of the resulting features in the etched semiconductor.