Fabrication of reflective layer on semiconductor light emitting devices

• US 8,309,377 B2
• Filed: 03/01/2005
• Issued: 11/13/2012
• Est. Priority Date: 04/07/2004
• Status: Expired due to Fees

• Current Assignee: Tinggi Technologies Pte., Ltd.
• Original Assignee: Tinggi Technologies Pte., Ltd.
• Inventors: Yuan, Shu, Kang, Xuejun
• Primary Examiner(s): Ghyka, Alexander
• Assistant Examiner(s): ISAAC, STANETTA D
• Application Number:
  US11/578,281
• Publication Number:
  US 20080121908A1
• Time in Patent Office: 2,814 Days
• Field of Search: 438/29
• US Class Current: 438/29
• CPC Class Codes: H01L 33/0093 Wafer bonding; Removal of the growth substrate
• CPC Class Codes: H01L 33/405 Reflective materials
• CPC Class Codes: H01L 33/64 Heat extraction or cooling elements

Abstract

Fabrication of Reflective Layer on Semiconductor Light emitting diodes A method for fabrication of a reflective layer on a semiconductor light emitting diode, the semiconductor light emitting diode having a wafer with multiple epitaxial layers on a substrate; the method comprising applying a first ohmic contact layer on a front surface of the multiple epitaxial layers, the first ohmic contact layer being of a reflective material to also act as a reflective layer.

Claims

1. A method for fabrication of a reflective layer on a semiconductor light emitting diode, the semiconductor light emitting diode being made from a wafer with multiple epitaxial layers on a substrate, the method comprising:

applying a first ohmic contact layer on a front surface of the multiple epitaxial layers, the first ohmic contact layer being of a reflective material to also act as a reflective layer at its interface with the front surface;

applying a second ohmic contact layer on a rear surface of the multiple epitaxial layers, wherein the second ohmic contact layer is transparent or semi-transparent;

applying to a front surface of the first ohmic contact layer a seed layer of a thermally conductive metal; and

electroplating a relatively thick layer of the thermally conductive metal on the seed layer, the relatively thick layer of the thermally conductive metal being electrically conductive such that only a single bonding wire is required for the semiconductor light emitting diode.

2. A method as claimed in claim 1, further comprising:

removing the substrate.

3. A method as claimed in claim 2, wherein after electroplating a relatively thick layer and before removing the substrate there is performed the additional step of annealing the wafer to improve adhesion.

4. A method as claimed in claim 2, wherein the second ohmic contact layer is applied after removing the substrate;

the second ohmic contact layer being one of blank and patterned.

5. A method as claimed in claim 4, wherein at least one bonding pad is formed on the second ohmic contact layer.

6. A method as claimed in claim 4, wherein the second ohmic contact layer does not cover the whole area of the second surface of the epitaxial layers.

7. A method as claimed in claim 4, wherein the second ohmic contact layer is formed on n-type layers of the epitaxial layers.

8. A method as claimed in claim 2, wherein after removing the substrate ohmic contact formation and subsequent process steps are carried out, the subsequent process steps including deposition of at least bonding pad.

9. A method as claimed in claim 8, wherein the exposed epitaxial layer is cleaned and etched before the second ohmic contact layer is deposited.

10. A method as claimed in claim 8, wherein after forming the second ohmic contact layer there is included testing of the light emitting devices on the wafer, and separating the wafer into individual devices.

11. A method as claimed in claim 2, wherein the thermally conductive metal comprises copper and the epitaxial layers comprise multiple GaN-related layers.

12. A method as claimed in claim 1, wherein the first ohmic contact layer is coated with an adhesion layer prior to application of the seed layer.

13. A method as claimed in claim 1, wherein the seed layer is patterned with photoresist patterns before the electroplating the relatively thick layer, the electroplating of the relatively thick layer being between the photoresist patterns.

14. A method as claimed in claim 13, wherein the photoresist patterns are of a height of at least 50 micrometers.

15. A method as claimed in claim 13, wherein the photoresist patterns have a thickness in the range of 3 to 500 micrometers.

16. A method as claimed in claim 13, wherein the photoresist patterns have a spacing of 300 micrometers.

17. A method as claimed in claim 1, wherein the electroplating a relatively thick layer of the thermally conductive metal on the seed layer comprises electroplating the seed layer without patterning, patterning being performed subsequently.

18. A method as claimed in claim 17, wherein patterning is by one of:

photoresist patterning and then wet etching, and laser beam micro-machining of the relatively thick layer.

19. A method as claimed in claim 1, wherein the relatively thick layer is of a height no greater than the photoresist height.

20. A method as claimed in claim 1, wherein the relatively thick layer of thermally conductive metal is electroplated to a height greater than the photoresist and is subsequently thinned by polishing.

21. A method as claimed in claim 1, wherein the light emitting devices are fabricated without one or more selected from the group consisting of:

lapping, polishing and dicing.

22. A method as claimed in claim 1, wherein the first ohmic contact layer is on p-type layers of the epitaxial layers.