GaN LED with solderable backside metal

• US 20030010975A1
• Filed: 07/05/2002
• Published: 01/16/2003
• Est. Priority Date: 07/05/2001
• Status: Active Grant

• Current Assignee: Current Lighting Solutions, LLC (f/k/a GE Lighting Solutions, LLC) (American Industrial Partners)
• Original Assignee: Gelcore (General Electric Company)
• Inventors: Karlicek, Robert F., Venugopalan, Hari S., Gibb, Shawn R., Eliashevich, Ivan, Mukerji, Prosanto K.
• Granted Patent: US 6,787,435 B2
• Time in Patent Office: Days
• US Class Current: 257/40
• 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 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• CPC Class Codes: H01L 33/40 Materials therefor
• 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

A light-emitting element (24) is disclosed. A light emitting diode (LED) includes a sapphire substrate (26) having front and back sides (33, 35), and a plurality of semiconductor layers (28, 30, 32) deposited on the front side (33) of the sapphire substrate (26). The semiconductor layers (28, 30, 32) define a light-emitting structure that emits light responsive to an electrical input. A metallization stack (40) includes an adhesion layer (34) deposited on the back side (35) of the sapphire substrate (26), and a solderable layer (38) connected to the adhesion layer (34) such that the solderable layer (38) is secured to the sapphire substrate (26) by the adhesion layer (34). A support structure (42) is provided on which the LED is disposed. A solder bond (44) is arranged between the LED and the support structure (42). The solder bond (44) secures the LED to the support structure (42).

Claims

1. A light-emitting diode comprising:

a stack of gallium nitride based layers configured to emit light responsive to an electrical input;

a light-transmissive substrate having a front side and a back side, the gallium nitride based layer stack disposed on the front side, the substrate being light-transmissive for the light produced by the gallium nitride based layer stack; and

a metallization stack including a solderable layer formed on the back side of said substrate, the metallization stack (i) reflecting a portion of the light produced by the gallium nitride based layer stack toward the front side of the substrate, and (ii) attaching the light-emitting diode to an associated support by a soldered bond.

2. The light emitting diode as set forth in claim 1, wherein the metallization stack further includes:

an adhesion layer directly adjacent to the back side of the substrate and secured to the back side of the substrate and secured to the solderable layer to effectuate a securing of the solderable layer to the substrate.

3. The light emitting diode as set forth in claim 2, wherein the adhesion layer is comprised of a material selected from a group consisting of silver, aluminum, and rhodium.

4. The light emitting diode as set forth in claim 2, wherein the metallization stack further includes:

a diffusion barrier layer arranged between the adhesion layer and the solderable layer that substantially prevents intermixing between the adhesion layer and the solderable layer.

5. The light emitting diode as set forth in claim 4, wherein the diffusion barrier layer is comprised of a material selected from a group consisting of titanium, nickel, platinum, and alloys thereof.

6. The light emitting diode as set forth in claim 4, wherein the diffusion barrier layer includes:

a first diffusion barrier layer secured to the adhesion layer; and

a second diffusion barrier layer secured to the solderable layer.

7. The light emitting diode as set forth in claim 6, wherein:

the adhesion layer is a silver layer;

the first diffusion barrier layer is a titanium layer; and

the second diffusion barrier layer is a nickel layer.

8. The light emitting diode as set forth in claim 6, wherein:

the adhesion layer is an aluminum layer;

the first diffusion barrier layer is a platinum layer; and

the second diffusion barrier layer is a nickel layer.

9. The light emitting diode as set forth in claim 2, wherein the solderable layer is selected from a group consisting of a gold layer and a silver layer.

10. A light-emitting element comprising:

a light emitting diode (LED) including a sapphire substrate having front and back sides, and a plurality of semiconductor layers deposited on the front side of the sapphire substrate, the semiconductor layers defining a light-emitting structure that emits light responsive to an electrical input;

a metallization stack including an adhesion layer deposited on the back side of the sapphire substrate, and a solderable layer connected to the adhesion layer such that the solderable layer is secured to the sapphire substrate by the adhesion layer;

a support structure on which the LED is disposed; and

a solder bond between the LED and the support structure that secures the LED to the support structure.

11. The light emitting element as set forth in claim 10, wherein the support structure is a lead frame or a heat sink.

12. The light emitting element as set forth in claim 10, wherein the metallization stack further includes:

a diffusion blocking layer disposed between the adhesion layer and the solderable layer that substantially reduces intermixing between the adhesion layer and the solderable layer.

13. The light emitting element as set forth in claim 12, wherein:

the adhesion layer is an aluminum layer, the diffusion blocking layer includes platinum and nickel, and the solderable layer is a gold layer.

14. The light emitting element as set forth in claim 12, wherein:

the adhesion layer is a silver layer, the diffusion blocking layer includes titanium and nickel, and the solderable layer is a gold layer.

15. The light emitting element as set forth in claim 10, wherein:

the adhesion layer is selected from a group consisting of an aluminum layer, a silver layer, and a rhodium layer.

16. The light emitting element as set forth in claim 10, further including:

front-side p-type and n-type contacts by which the electrical input is applied to the semiconductor layers defining the light-emitting structure.

17. The light emitting element as set forth in claim 10, wherein the plurality of semiconductor layers are selected from a group consisting of GaN, AlN, InN, and alloys thereof.

19. The method as set forth in claim 18, wherein the step of depositing a metallic bonding layer includes:

depositing an adhesion layer on the back side of the substrate; and

depositing a solderable layer on the adhesion layer.

20. The method as set forth in claim 18, wherein the step of depositing a metallic bonding layer includes:

depositing an adhesion layer on the back side of the substrate;

depositing a diffusion blocking layer on the adhesion layer; and

depositing a solderable layer on the diffusion blocking layer.

25. The method as set forth in claim 18, wherein the step of depositing a metallic bonding layer includes:

depositing a first layer comprised of at least one of silver and aluminum;

depositing a second layer comprised of at least one of silver, aluminum, and rhodium on the first layer; and

depositing a third layer comprised of at least one of silver, gold, and tin on the second layer.

26. The method as set forth in claim 18, further including:

subsequent to the step of depositing a metallic bonding layer and prior to the soldering and connecting steps, dicing the substrate wafer to form a plurality of LED chips, wherein the subsequent soldering and connecting steps are applied to and repeated for each of the plurality of LED chips.

27. The method as set forth in claim 18, further including:

annealing the metallic bonding layer at a selected temperature for a selected time in a selected ambient.

29. The method as set forth in claim 18, further including:

prior to the depositing of the metallic bonding layer, thinning the back side of the substrate wafer to a selected reduced thickness; and

subsequent to the depositing of the metallic bonding layer, dicing the substrate wafer to produce LED chips that are individually processed in the soldering and connecting steps.

18. A method for fabricating a light-emitting element, the method comprising:

depositing semiconducting layers on a front side of an electrically insulating substrate wafer such that the semiconducting layers define a light-emissive region that emits light responsive to an electrical current flowing therethrough;

forming electrical contacts contacting selected semiconducting layers;

depositing a metallic bonding layer on a back side of the substrate;

soldering the metallic bonding layer to a support structure; and

connecting the electrical contacts to electrical inputs that supply the electrical current to the light-emissive region.

21. The method as set forth in claim 78, wherein the electrically insulating substrate is a sapphire substrate.

22. The method as set forth in claim 21, wherein the step of depositing a metallic bonding layer includes:

depositing a silver layer on the substrate;

depositing a second layer onto the silver layer, the second layer including at least one of a titanium layer and a nickel layer; and

depositing a solderable layer on the second layer, the solderable layer selected from a group consisting of silver, gold, and tin.

23. The method as set forth in claim 21, wherein the step of depositing a metallic bonding layer includes:

depositing an aluminum layer on the substrate;

depositing a second layer on the aluminum layer, the second layer including at least one of a platinum layer and a nickel layer; and

depositing a solderable layer on the second layer, the solderable layer selected from a group consisting of silver, gold, and tin.

28. The method as set forth in claim 27, wherein the substrate wafer is a sapphire wafer, and the selected temperature is between about 200°

C. and about 400°

C.

30. The method as set forth in claim 29, wherein the support structure includes a plurality of support structures and the soldering step includes soldering at least one LED chip to each support structure.

31. The method as set forth in claim 29, wherein the soldering step includes:

applying a solder material to the support structure to define a plurality of solder pads on the support structure;

approximately aligning each LED chip onto a corresponding solder pad; and

reflowing the solder to effectuate solder bonding of the LED chips to the support structure and self-alignment of the LED chips with the solder pads.

24. The method as set forth in claim 78, wherein the step of depositing semiconducting layers includes:

depositing a plurality of layers defining a p/n diode structure wherein the layers are selected from a group consisting of AlN, GaN, InN, and alloys thereof.

32. A light emitting diode (LED) comprising:

a substrate;

a stack of semiconductor layers arranged on a first side of the substrate, the stack of semiconductor layers configured to emit light responsive to an electrical input; and

a metallization stack arranged on a second side of the substrate opposite the first side, the metallization stack including a plurality of layers, said layers including at least;

(i) a first layer formed from a first material that adheres to the substrate, and (ii) a second layer formed from a second material that is suitable for solder bonding, the second material being different from the first material.

33. The LED as set forth in claim 32, wherein the metallization stack further includes:

a third layer interposed between the first and second layers and substantially reducing intermixing of the first and second materials.