Method of forming a micro LED structure and array of micro LED structures with an electrically insulating layer
A method of fabricating and transferring a micro device and an array of micro devices to a receiving substrate are described. In an embodiment, an electrically insulating layer is utilized as an etch stop layer during etching of a p-n diode layer to form a plurality of micro p-n diodes. In an embodiment, an electrically conductive intermediate bonding layer is utilized during the formation and transfer of the micro devices to the receiving substrate.
1. A method of forming a micro LED array in the following sequence comprising:
bonding a first substrate stack to a second substrate stack with a bonding layer;
wherein the first substrate stack comprises:
a p-n diode layer formed on a first substrate;
a plurality of separate reflective metallization stacks on the p-n diode layer;
a patterned electrically insulating layer laterally between the plurality of separate reflective metallization stacks on the p-n diode layer;
removing the first substrate; and
etching through the p-n diode layer to form a plurality of micro p-n diodes over the plurality of separate reflective metallization stacks, and exposing the patterned electrically insulating layer laterally between the plurality of micro p-n diodes, wherein the patterned electrically insulating layer acts as an etch stop layer during the etching.
2. The method of claim 1 :
wherein the first substrate stack comprises a first electrically conductive bonding layer over the patterned electrically insulating layer and the plurality of separate reflective metallization stacks, and the second substrate stack comprises a second electrically conductive bonding layer; and
wherein bonding the first substrate stack to the second substrate stack further comprises bonding the first electrically conductive bonding layer to the second electrically conductive bonding layer to form an alloy bonding layer.
3. The method of claim 2 , wherein one of the first and second electrically conductive bonding layers has a liquidus temperature below 350° C., and the alloy bonding layer has a liquidus temperature below 350° C.
4. The method of claim 2 , wherein one of the first and second electrically conductive bonding layers has a liquidus temperature below 200° C., and the alloy bonding layer has a liquidus temperature below 200° C.
5. The method of claim 3 , wherein one of the first and second electrically conductive bonding layers comprises a material selected from the group consisting of indium and tin.
6. The method of claim 5 , wherein one of the first and second electrically conductive bonding layers has a thickness which is 5% or less a thickness of the other one of the first and second electrically conductive bonding layers.
7. The method of claim 2 , wherein the first electrically conductive bonding layer is completely consumed in the alloy bonding layer at locations where the first electrically conductive bonding layer makes contacts with the second electrically conductive bonding layer.
8. The method of claim 7 , wherein bonding the first electrically conductive bonding layer to the second electrically conductive bonding layer comprises maintaining the first and second electrically conductive bonding layers at an elevated temperature above a liquidus temperature of one of the first and second electrically conductive bonding layers.
9. The method of claim 1 , further comprising patterning a reflective metallization stack layer on the p-n diode layer to form the plurality of separate reflective metallization stacks on the p-n diode layer.
10. The method of claim 9 , further comprising depositing an electrically insulating layer over the plurality of separate reflective metallization stacks.
11. The method of claim 10 , further comprising patterning the electrically insulating layer to form the patterned electrically insulating layer including a plurality of openings exposing the plurality of separate reflective metallization stacks.
12. The method of claim 11 , further comprising depositing a first electrically conductive bonding layer over the patterned electrically insulating layer and the plurality of separate reflective metallization stacks.
13. The method of claim 1 , further comprising etching the patterned electrically insulating layer after stopping the etching of the p-n diode layer to expose a bottom surface of each of the plurality of micro p-n diodes.
14. The method of claim 13 , further comprising depositing a conformal dielectric barrier layer on side surfaces and the bottom surface of each of the plurality of micro p-n diodes.
15. The method of claim 14 , wherein the conformal dielectric barrier layer covers a side surface of a quantum well layer in the micro p-n diode.
16. The method of claim 1 , wherein etching the p-n diode layer to form the plurality of micro p-n diodes comprises plasma etching.
17. The method of claim 16 , wherein each of the plurality of micro p-n diodes includes a top surface, a bottom surface and tapered sidewalls, wherein the bottom surface is wider than the top surface.
18. The method of claim 1 , further comprising depositing an electrically insulating layer over the plurality of separate reflective metallization stacks.
19. The method of claim 18 , further comprising patterning the electrically insulating layer to form the patterned electrically insulating layer including a plurality of openings exposing the plurality of separate reflective metallization stacks.
20. The method of claim 19 , wherein the plurality of separate reflective metallization stacks are wider than the plurality of openings exposing the plurality of separate reflective metallization stacks.
21. The method of claim 20 , wherein the bonding layer comprises an electrically conductive material.
22. The method of claim 21 , wherein the bonding layer comprises a metal or metal alloy.
23. The method of claim 20 , wherein the bonding layer comprises a polymer.
24. The method of claim 20 , further comprising etching the patterned electrically insulating layer after etching of the p-n diode layer to remove the patterned electrically insulating layer from underneath a bottom surface of each of the plurality of micro p-n diodes.
25. The method of claim 20 , further comprising embedding a topography of the patterned electrically insulating layer into the bonding layer during the bonding the first substrate stack to the second substrate stack.
26. The method of claim 1 , wherein the patterned electrically insulating layer of the first substrate stack includes a plurality of openings exposing the plurality of separate reflective metallization stacks, the plurality of separate reflective metallization stacks are wider than the plurality of openings exposing the plurality of separate reflective metallization stacks, and a portion of the electrically insulating layer is formed on top of each of the separate reflective metallization stacks opposite the p-n diode layer.
27. The method of claim 26 , further comprising embedding a topography of the patterned electrically insulating layer into the bonding layer during the bonding the first substrate stack to the second substrate stack.
28. The method of claim 27 , wherein the bonding layer comprises a metal or metal alloy.
29. The method of claim 27 , wherein the bonding layer comprises a polymer.
30. The method of claim 27 , further comprising etching the patterned electrically insulating layer after etching of the p-n diode layer to remove the patterned electrically insulating layer from underneath a bottom surface of each of the plurality of micro p-n diodes.