LED units fabrication method

1. A method for fabricating a plurality of individual light emitting diode units, comprising:

providing a sapphire substrate;

forming a GaN epitaxial layer on the sapphire substrate;

forming a plurality of exhaust trenches on the GaN epitaxial layer, wherein the exhaust trenches define a plurality of individual light emitting diode units;

forming a reflective layer on the GaN epitaxial layer;

attaching the reflective layer to a conductive substrate;

removing the sapphire substrate from the GaN epitaxial layer via a laser lift-off process, wherein a gas produced during the laser lift-off process is exhausted via the exhaust trenches; and

dicing the conductive substrate along the exhaust trenches to form the plurality of individual light emitting diode units;

wherein formation of the reflective layer comprises depositing a reflective layer on the GaN epitaxial layer using plasma-enhanced chemical vapor deposition.

2. The method of claim 1 , wherein formation of the GaN epitaxial layer comprises forming an n-GaN layer, an active layer, and a p-GaN layer on the sapphire substrate in that order via metal oxide chemical vapor deposition.

3. The method of claim 1 , wherein formation of the exhaust trenches uses inductive couple plasma reactive ion etching.

4. The method of claim 1 , wherein the exhaust trenches define a preserve region in a middle portion of the GaN epitaxial layer, and a sacrifice region in a marginal portion of the GaN epitaxial layer; wherein the plurality of individual light emitting diode units is formed in the preserve region.

5. The method of claim 4 , wherein the plurality of individual light emitting diode units has the same shape, and is arranged in rows along the exhaust trenches.

6. The method of claim 5 , wherein a light spot projected on the GaN epitaxial layer by a laser beam has the same shape and size as an individual light emitting diode unit during the laser lift-off process.

7. The method of claim 6 , wherein the laser lift-off process further comprises:

projecting an initial light spot on the sacrifice region adjacent to a first row of the individual light emitting diode units;

moving the initial light spot along the exhaust trench into the preserve region, and scanning each individual light emitting diode units of the row one by one;

stopping laser beam emission when the initial light spot passes through the preserve region;

projecting a new light spot on the sacrifice region adjacent to a second row of the individual light emitting diode units, the second row being adjacent to the first row; and

repeating movement of the initial light spot along the exhaust trench until each row of the individual light emitting diode units is scanned.

8. The method of claim 7 , wherein the initial light spot entirely covers at least one individual light emitting diode unit during movement of the initial light spot.

9. The method of claim 7 , wherein the initial light spot intercrosses a rim of the GaN epitaxial layer.

10. A method for fabricating a plurality of individual light emitting diode units, comprising:

providing a sapphire substrate;

forming a GaN epitaxial layer on the sapphire substrate;

forming a plurality of exhaust trenches on the GaN epitaxial layer, wherein the exhaust trenches define a plurality of individual light emitting diode units;

forming a reflective layer on the GaN epitaxial layer;

attaching the reflective layer to a conductive substrate;

removing the sapphire substrate from the GaN epitaxial layer via a laser lift-off process, wherein a gas produced during the laser lift-off process is exhausted via the exhaust trenches; and

dicing the conductive substrate along the exhaust trenches to form the plurality of individual light emitting diode units;

wherein the exhaust trenches define a preserve region in a middle portion of the GaN epitaxial layer, and a sacrifice region in a marginal portion of the GaN epitaxial layer; wherein the plurality of individual emitting diode units is formed in the preserve region;

wherein the plurality of individual light emitting diode units has the same shape, and is arranged in rows along the exhaust trenches; and

wherein a light spot projected on the GaN epitaxial layer by a laser beam has the same shape and size as an individual light emitting diode unit during the laser lift-off process.

11. The method of claim 10 , wherein the laser lift-off process further comprises:

projecting an initial light spot the sacrifice region adjacent to a first row of the individual light emitting, diode units;

moving the initial light spot along the exhaust trench into the preserve region, and scanning each individual light emitting diode units of the row one by one;

stopping laser beam emission when the initial light spot passes through the preserve region;

projecting a new light spot on the sacrifice region adjacent to a second row of the individual light emitting diode units, the second row being adjacent the first row; and

repeating movement of the initial light spot along the exhaust trench until each row of the individual light emitting diode units is scanned.

12. The method of claim 11 , wherein the initial light spot entirely covers at least one individual light emitting diode unit during movement of the initial light spot.

13. The method of claim 11 , wherein the initial light spot intercrosses a rim of the GaN epitaxial layer.