Method to remove sapphire substrate

1. A method of fabricating a light-emitting diode (LED) comprising:

providing a sapphire substrate;

forming an undoped buffer layer over the sapphire substrate;

forming a light-emitting structure over the undoped buffer layer, said structure comprising:

a first doped layer doped with a first impurity of a first conductivity type;

an active layer over the first doped layer; and

a second doped layer over the active layer, the second doped layer doped with a second impurity of a second conductivity type opposite the first conductivity type;

removing a first portion of the sapphire substrate by grinding a back surface of the sapphire substrate;

thereafter removing the sapphire substrate in its entirety by etching; and

thereafter removing a portion of the undoped buffer layer so as to form a recess in the undoped buffer layer.

2. The method of claim 1 , wherein after the removing the first portion, the sapphire substrate in its entirety has a thickness in a range from about 3 μm to 6 μm.

3. The method of claim 1 , wherein the grinding the back surface of the sapphire substrate comprises sequentially using two abrasives having different hardness or particle sizes.

4. The method of claim 1 , wherein the etching includes an etching process using a plasma.

5. The method of claim 4 , wherein the plasma is inductively coupled plasma.

6. The method of claim 5 , wherein the plasma includes halogen containing etchants.

7. The method of claim 1 , wherein the etching is wet etching.

8. The method of claim 7 , wherein the wet etching comprises exposing the substrate to a solution of sulfuric acid, phosphoric acid, or a solution including both sulfuric acid and phosphoric acid.

9. The method of claim 8 , wherein a temperature of the solution is greater than 110° C., and wherein a pressure of the solution is greater than one atmosphere pressure.

10. The method of claim 1 ,

wherein the undoped buffer layer and the sapphire substrate have different material compositions.

11. A method of fabricating a LED, comprising:

providing a growth substrate;

forming a light-emitting structure on the growth substrate, said structure comprising:

a buffer layer;

a first doped layer on the buffer layer, said first doped layer doped with a first impurity of a first conductivity type;

an active layer over the first doped layer; and

a second doped layer over the active layer, the second doped layer doped with a second impurity of a second conductivity type opposite the first conductivity type;

forming a patterned contact metal layer on the second doped layer;

forming, after the forming the patterned contact metal layer, a patterned reflecting metal layer on the patterned contact metal layer;

forming, after the forming the patterned reflecting metal layer, a photoresist layer on the patterned reflecting metal layer;

forming, after the forming the photoresist layer and using the photoresist layer as a mesa pattern, a plurality of streets into the light-emitting structure, thereby forming a plurality of light-emitting mesa structures with exposed sidewalls;

depositing, after the forming the plurality of light-emitting mesa structures, a passivation layer to cover the exposed sidewalls;

removing, after the depositing the passivation layer, a portion of the passivation layer to expose a surface of the reflecting metal layer;

forming, after the surface of the reflecting metal layer has been exposed, a bonding metal layer on the exposed surface of the reflecting metal layer;

bonding, after the forming the bonding metal layer, the growth substrate to a silicon substrate having an adhesion metal layer formed thereon, wherein the bonding metal layer of the growth substrate is bonded to the adhesion metal layer of the silicon substrate;

after the bonding, removing a first portion of the growth substrate by grinding a back surface of the growth substrate, wherein the growth substrate not removed by the grinding is a second portion of the growth substrate; and

completely removing the second portion of the growth substrate by etching.

12. The method of claim 11 , further comprising removing at least a portion of the buffer layer after completely removing the second portion of the growth substrate, wherein the buffer layer contains an undoped material that is different from a material of the growth substrate.

13. The method of claim 12 , wherein the removing the at least the portion of the buffer layer exposes a surface of the first doped layer, and further comprising:

roughing a first portion of the exposed surface of the first doped layer; and

forming a metal contact on a second portion of the exposed surface of the first doped layer.

14. The method of claim 13 , further comprising:

forming a temporary contact on the adhesion metal layer;

applying a voltage across the temporary contact and the metal contact on the first doped layer so that a light is emitted from at least one of the light-emitting mesa structures;

measuring the light emitted by the at least one of the light-emitting mesa structures; and

binning the at least one of the light-emitting mesa structures based on the measuring of the emitted light.

15. The method of claim 11 , wherein the etching comprises using capacitively coupled plasma (CCP), inductively coupled plasma (ICP), magnetron plasma, electron cyclotron resonance (ECR) plasma, or microwave plasma.

16. The method of claim 11 , wherein the etching comprises exposing the substrate to a solution of H 2 SO 4 , H 3 PO 4 , or a solution including both H 2 SO 4 and H 3 PO 4 .

17. A method of fabricating a LED, comprising:

providing a growth substrate;

forming a light-emitting structure on the growth substrate, said structure comprising:

a buffer layer;

a first doped layer on the buffer layer, said first doped layer doped with a first impurity of a first conductivity type;

an active layer over the first doped layer; and

a second doped layer over the active layer, the second doped layer doped with a second impurity of a second conductivity type opposite the first conductivity type;

etching a plurality of streets into the light-emitting structure forming a plurality of light-emitting mesa structures;

removing a first portion of the growth substrate by grinding a back surface of the growth substrate so that a remaining portion of the growth substrate is a rest of the growth substrate not removed by the grinding;

completely removing the remaining portion of the growth substrate in its entirety by plasma etch or wet etch; and

thereafter forming a recess in the buffer layer by removing a portion of the buffer layer.

18. The method of claim 1 , further comprising: before the removing the first portion of the sapphire substrate, bonding the sapphire substrate to a silicon substrate, wherein the light-emitting structure is bonded between the sapphire substrate and the silicon substrate.

19. The method of claim 18 , further comprising: before the bonding:

forming a contact layer on the second doped layer;

forming a reflecting metal layer on the contact layer; and

forming a bonding metal on the reflecting metal layer;

wherein the bonding is performed such that the bonding metal is bonded between the reflecting metal layer and the silicon substrate.

20. The method of claim 17 , wherein the buffer layer is undoped and has a different material composition than the growth substrate, and further comprising:

before the removing the first portion of the growth substrate, bonding the growth substrate to a silicon substrate.