Method for controlling the structure and surface qualities of a thin film and product produced thereby

• US 20070111345A1
• Filed: 02/17/2006
• Published: 05/17/2007
• Est. Priority Date: 11/14/2005
• Status: Active Grant

• Current Assignee: Palo Alto Research Center, Inc. (Xerox Holdings Corp.)
• Original Assignee: Palo Alto Research Center, Inc. (Xerox Holdings Corp.)
• Inventors: Wong, William, Teepe, Mark, Kneissl, Michael
• Granted Patent: US 7,501,299 B2
• Time in Patent Office: Days
• US Class Current: 438/22
• CPC Class Codes: B82Y 20/00 Nanooptics, e.g. quantum optics or photonic crystals
• CPC Class Codes: H01L 33/0093 Wafer bonding; Removal of the growth substrate
• CPC Class Codes: H01S 5/0213 Sapphire, quartz or diamond based substrates
• CPC Class Codes: H01S 5/0216 using an intermediate compound, e.g. a glue or solder
• CPC Class Codes: H01S 5/0217 Removal of the substrate
• CPC Class Codes: H01S 5/32341 blue laser based on GaN or GaP
• CPC Class Codes: H01S 5/34333 with a well layer based on Ga(In)N or Ga(In)P, e.g. blue laser

Abstract

A system and method for providing improved surface quality following removal of a substrate and template layers from a semiconductor structure provides an improved surface quality for a layer (such as a quantum well heterostructure active region) prior to bonding a heat sink/conductive substrate to the structure. Following the physical removal of a sapphire substrate, a sacrificial coating such as a spin-coat polymer photoresist is applied to an exposed GaN surface. This sacrificial coating provides a planar surface, generally parallel to the planes of the interfaces of the underlying layers. The sacrificial coating and etching conditions are selected such that the etch rate of the sacrificial coating approximately matches the etch rate of GaN and the underlying layers, so that the physical surface profile during etching approximates the physical surface profile of the sacrificial coating prior to etching. Following etching, a substrate is bonded to the exposed surface which acts as a heat sink and may be conductive providing for backside electrical contact to the active region.

Claims

1. A method of fabricating a semiconductor device in which a relatively high aluminum content layer is formed over an Al₂O₃ substrate and a GaN buffer layer formed over and in physical contact with the Al₂O₃ substrate so as to create a bond at an interface between the GaN layer and the Al₂O₃ substrate, comprising:

weakening the bond between the GaN layer and the Al₂O₃ substrate by irradiating, through the Al₂O₃ substrate, the interface between the GaN layer and the Al₂O₃ substrate;

physically removing the Al₂O₃ substrate to thereby expose a surface of the GaN layer;

applying a planarizing coating over and in physical contact with the exposed surface of the GaN layer;

etching the planarized coating and GaN layer to at least significantly remove both; and

securing a thermally conductive substrate over said relatively high aluminum content layer on the side thereof previously occupied by the Al₂O₃ substrate and GaN layer.

2. The method of claim 1, further comprising, following the step of etching and before the step of securing an electrically conductive substrate, forming at least one intermediate layer over and in physical contact with a surface exposed by said etching step.

3. The method of claim 1, wherein said planarizing coating is photoresist, which is spun onto the exposed surface of the GaN layer.

4. The method of claim 1, further comprising the step of polishing the planarized coating prior to etching.

5. A method of fabricating a surface emitting light emitting device capable of emitting light in the ultra violet wavelengths from a structure of the type in which a high aluminum content multiple quantum well active region is formed over an Al₂O₃ substrate and a GaN buffer layer formed over and in physical contact with the Al₂O₃ substrate so as to create a bond at an interface between the GaN layer and the Al₂O₃ substrate, comprising:

weakening the bond between the GaN layer and the Al₂O₃ substrate by irradiating, through the Al₂O₃ substrate, the interface between the GaN layer and the Al₂O₃ substrate;

physically removing the Al₂O₃ substrate to thereby expose a surface of the GaN layer;

applying a planarizing coating over and in physical contact with the exposed surface of the GaN layer;

etching the planarized coating, and GaN layer to at least significantly remove both; and

securing an electrically conductive substrate over said high aluminum content multiple quantum well active region on the side thereof previously occupied by the Al₂O₃ substrate and GaN layer.

6. The method of claim 5, further comprising, following the step of etching and before the step of securing an electrically conductive substrate, forming at least one intermediate layer over and in physical contact with a surface exposed by said etching step.

7. The method of claim 6, wherein said intermediate layer is reflective at the wavelength of emission of the light emitting device, to thereby form one side of a lasing cavity for a semiconductor laser.

8. The method of claim 5, wherein the light emitting device is a light emitting diode.

9. The method of claim 5, wherein said planarizing coating is photoresist, which is spun onto the exposed surface of the GaN layer.

10. The method of claim 5, further comprising the step of polishing the planarized coating prior to etching.

20. The method of claim 10, further comprising the step of polishing the planarized coating prior to etching.

11. A method of fabricating a surface emitting light emitting device capable of emitting light in the ultra violet wavelengths, comprising the steps of:

forming over and in contact with a Al₂O₃ substrate a GaN template layer such that a physical bond is created at an interface between the GaN layer and the Al₂O₃ substrate;

forming over and in contact with said GaN template layer a superlattice structure, said superlattice structure comprising a plurality of layer pairs, a first layer of said layer pairs being AlN and a second layer of said layer pairs being GaN;

forming over said superlattice structure a multiple quantum well heterostructure;

forming over said multiple quantum well heterostructure a contact layer;

securing an intermediate substrate to said contact layer;

removing said Al₂O₃ substrate;

applying a planarizing coating over and in physical contact with the exposed surface of the GaN layer;

etching the planarized coating, and GaN layer to at least significantly remove both; and

securing said semiconductor light emitting device to a permanent substrate at a surface opposite said intermediate substrate.

12. The method of fabricating a surface emitting light emitting device of claim 11, wherein the step of removing said Al₂O₃ substrate comprises:

weakening the bond between the GaN layer and the Al₂O₃ substrate by irradiating, through the Al₂O₃ substrate, the interface between the GaN layer and the Al₂O₃ substrate; and

physically removing the Al₂O₃ substrate to thereby expose a surface of the GaN layer.

13. The method of fabricating a surface emitting light emitting device of claim 11, wherein said permanent substrate is electrically conductive, and forms an electrical contact with said multiple quantum well heterostructure.

14. The method of fabricating a surface emitting light emitting device of claim 11, wherein said intermediate substrate is transparent to light in the ultra violet spectrum.

15. The method of fabricating a surface emitting light emitting device of claim 11, further comprising the step of removing said intermediate substrate.

16. The method of fabricating a surface emitting light emitting device of claim 11, further comprising, following the step of etching and before the step of securing an electrically conductive substrate, forming at least one intermediate layer over and in physical contact with a surface exposed by said etching step.

17. The method of claim 16, wherein said intermediate layer is reflective at the wavelength of emission of the light emitting device, to thereby form one side of a lasing cavity for a semiconductor laser.

18. The method of claim 11, wherein the light emitting device is a light emitting diode.

19. The method of claim 11, wherein said planarizing coating is photoresist, which is spun onto the exposed surface of the GaN layer.