Increased light extraction from a nitride LED

• US 7,125,734 B2
• Filed: 03/09/2005
• Issued: 10/24/2006
• Est. Priority Date: 03/09/2005
• Status: Expired due to Fees

• Current Assignee: Gelcore (General Electric Company)
• Original Assignee: Gelcore (General Electric Company)
• Inventors: Gao, Xiang, Venugopalan, Hari S., Sackrison, Michael J.
• Primary Examiner(s): Fourson, George
• Assistant Examiner(s): Pham, Thanh V.
• Application Number:
  US11/075,974
• Publication Number:
  US 20060202223A1
• Time in Patent Office: 594 Days
• Field of Search: 438 25- 27, 438 33- 35, 438/38, 438/41, 250/239, 257 80- 85, 257/E33.057
• US Class Current: 438/25
• CPC Class Codes: H01L 2224/0554 External layer
• CPC Class Codes: H01L 2224/0555 Shape
• CPC Class Codes: H01L 2224/0556 Disposition
• CPC Class Codes: H01L 2224/05568 the whole external layer protruding from the surface
• CPC Class Codes: H01L 2224/05573 Single external layer
• CPC Class Codes: H01L 2224/05599 Material
• CPC Class Codes: H01L 2224/05644 Gold [Au] as principal constituent
• CPC Class Codes: H01L 2224/16 of an individual bump connector
• 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 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 33/62 Arrangements for conducting electric current to or from the semiconductor body, e.g. lead-frames, wire-bonds or solder balls

Abstract

In a method for fabricating a flip-chip light emitting diode device, a submount wafer is populated with a plurality of the light emitting diode dies. Each device die is flip-chip bonded to the submount. Subsequent to the flip-chip bonding, a growth substrate is removed. The entire submount is immersed in the etchant solution, exposed to the light for a prespecified period of time, removed from the solution, dried and diced into a plurality of LEDs. The LEDs are immediately packaged without any further processing.

Claims

1. A method for fabricating a light emitting device comprising:

depositing epitaxial layers on a growth substrate to produce an epitaxial wafer;

fabricating a plurality of light emitting diode devices with a lateral current flow geometry on the epitaxial wafer;

dicing the epitaxial wafer to generate a plurality of light emitting dies;

flip chip bonding at least one electrode of one or more die to at least one bonding pad of a mount;

subsequent to bonding of the dies, removing the growth substrate to expose an epitaxial layer; and

roughening the epitaxial layer by electrode-less photochemical etching.

2. The method as set forth in claim 1, wherein the step of roughening includes:

immersing the mount carrying the device dies in a chemical solution for a prespecified time period; and

concurrently illuminating the immersed exposed epitaxial layer with a light source.

3. The method as set forth in claim 2, further including:

removing the mount carrying the device dies from the chemical solution;

rinsing the mount carrying the device dies with water;

drying the mount carrying the device dies;

dicing the mount to generate a plurality of light emitting diode chips; and

packaging the light emitting diode chips.

4. The method as set forth in claim 2, wherein the chemical etching includes:

selecting a chemical etchant that etches the exposed layer to produce a plurality of microstructures about a top surface of the exposed layer.

5. The method as set forth in claim 2, wherein the chemical solution has ambient temperature.

6. The method as set forth in claim 2, wherein the chemical solution is at least one of:

Potassium Hydroxide, and

Hydrochloric Acid.

7. The method as set forth in claim 2, wherein the light source includes frequencies above the bandgap of the exposed epitaxial layer, the light source being at least one of:

a laser light;

a mercury-xenon arc lamp;

a mercury arc lamp; and

a UV light.

8. The method as set forth in claim 1, further including:

cleaning the exposed epitaxial layer prior to roughening.

9. The method as set forth in claim 1, further including:

deposing an underfill material at least between the mount and the flip chip bonded device die.

10. The method as set forth in claim 9, further including:

deposing a phosphor in the underfill material.

11. The method as set forth in claim 9, wherein the underfill material is selected to have a thermal expansion coefficient matching one of a thermal expansion coefficient of the device die, a thermal expansion coefficient of the mount, and a thermal expansion coefficient value intermediate between the thermal expansion coefficients of the device die and the mount.

12. The method as set forth in claim 1, wherein the epitaxial layers include group III-nitride compound semiconductor layers.

13. The method as set forth in claim 12, wherein the growth substrate is a sapphire substrate.

14. A method for fabricating a Group III Nitride semiconductor lateral current light emitting diode device comprising:

depositing epitaxial layers on a growth substrate to produce an epitaxial wafer;

fabricating a plurality of light emitting diode devices on the epitaxial wafer;

dicing the epitaxial wafer to generate a plurality of light emitting diode device dies, each including laterally disposed first and second electrodes;

flip chip bonding the device dies to a mount, the flip chip bonding including securing the device dies to the mount by bonding the first and second electrodes of each device die to corresponding bonding pads of the mount;

subsequent to the flip chip bonding of the device dies, removing the growth substrate to expose an epitaxial layer;

roughening the exposed epitaxial layer being exposed by the substrate removal by electrode-less photochemical etching without applying a bias, including;

immersing the mount, carrying the device dies, in a chemical solution for a prespecified time period, and

concurrently illuminating the immersed exposed epitaxial layer with a light source;

removing the mount carrying the device dies from the chemical solution;

rinsing the mount carrying the device dies;

drying the mount carrying the device dies;

dicing the mount to generate a plurality of light emitting diode chips; and

packaging the light emitting diode chips.