LED wafer with laminated phosphor layer
View Patent ↗An LED wafer with a growth substrate is attached to a carrier substrate by, for example, a heat-releasable adhesive so that the LED layers are sandwiched between the two substrates. The growth substrate is then removed, such as by laser lift-off. The exposed surface of the LED layers is then etched to improve light extraction. A preformed phosphor sheet, matched to the LEDs, is then affixed to the exposed LED layer. The phosphor sheet, LED layers, and, optionally, the carrier substrate are then diced to separate the LEDs. The LED dice are released from the carrier substrate by heat or other means, and the individual LED dice are mounted on a submount wafer using a pick-and-place machine. The submount wafer is then diced to produce individual LEDs. The active layer may generate blue light, and the blue light and phosphor light may generate white light having a predefined white point.
1. A method for fabricating a light emitting diode (LED) device comprising:
growing LED layers on a growth substrate;
providing a preformed phosphor sheet separate from the LED layers;
affixing the LED layers to a carrier substrate using a releasable adhesive;
removing the growth substrate while the carrier substrate provides mechanical support for the LED layers;
laminating the preformed phosphor sheet to an exposed surface of the LED layers;
dicing the phosphor sheet and the LED layers to create separate LED dice, each having an overlying phosphor layer;
releasing the LED layers from the releasable adhesive; and
removing the LED dice from the carrier substrate.
2. The method of claim 1 wherein the LED layers comprise an n-layer and a p-layer, the method further comprising forming metal electrodes contacting the n-layer and the p-layer prior to affixing the LED layers to the carrier substrate.
3. The method of claim 2 wherein affixing the LED layers to the carrier substrate comprises affixing at least some of the metal electrodes to the carrier substrate.
4. The method of claim 1 wherein the LED layers emit blue light when energized, and the phosphor sheet emits red light wavelengths and green light wavelengths when energized by the blue light, such that the LED dice emit white light when the LED dice are energized.
5. The method of claim 4 wherein the phosphor sheet comprises a YAG phosphor.
6. The method of claim 1 wherein the phosphor sheet has an area approximately the same as or larger than an area of the growth substrate.
7. The method of claim 1 wherein the phosphor sheet has a substantially uniform thickness.
8. The method of claim 1 further comprising mounting the carrier substrate on an adhesive sheet, and wherein dicing the phosphor sheet and the LED layers comprises also dicing the carrier substrate but not the adhesive sheet.
9. The method of claim 1 wherein removing the growth substrate comprises removing the growth substrate using a laser lift-off process.
10. The method of claim 1 wherein the releasable adhesive comprises an adhesive releasable by at least one of UV light, heat, or a solvent.
11. The method of claim 1 further comprising mounting the LED dice on a submount wafer by bonding electrodes on the submount wafer to corresponding electrodes of the LED dice.
12. The method of claim 1 further comprising using a pick-and-place machine to remove the LED dice individually from the carrier substrate.
13. A light emitting diode (LED) structure comprising:
an LED wafer, including a growth substrate, the LED wafer having a first surface;
a carrier substrate affixed to the first surface by a releasable adhesive, wherein the growth substrate is removed from the LED wafer, the LED wafer having a second surface opposite to the first surface; and
a preformed phosphor sheet, formed separate from the LED wafer, affixed to the second surface of the LED wafer,
wherein the phosphor sheet and LED wafer are not yet diced.
14. The device of claim 13 further comprising the carrier substrate being affixed to a stretchable sheet for supporting the phosphor sheet, the LED wafer, and the carrier substrate after dicing of the phosphor sheet, the LED wafer, and the carrier substrate.
15. The device of claim 13 wherein the LED wafer comprises an n-layer and a p-layer, the LED wafer further comprising metal electrodes contacting at least the p-layer, the carrier substrate being affixed to the metal electrodes by the releasable adhesive.