Printable inorganic semiconductor structures
View Patent ↗The present invention provides structures and methods that enable the construction of micro-LED chiplets formed on a sapphire substrate that can be micro-transfer printed. Such printed structures enable low-cost, high-performance arrays of electrically connected micro-LEDs useful, for example, in display systems. Furthermore, in an embodiment, the electrical contacts for printed LEDs are electrically interconnected in a single set of process steps. In certain embodiments, formation of the printable micro devices begins while the semiconductor structure remains on a substrate. After partially forming the printable micro devices, a handle substrate is attached to the system opposite the substrate such that the system is secured to the handle substrate. The substrate may then be removed and formation of the semiconductor structures is completed. Upon completion, the printable micro devices may be micro transfer printed to a destination substrate.
1. A method of making an inorganic semiconductor structure suitable for micro-transfer printing, comprising:
providing a source substrate;
forming a semiconductor layer on the source substrate, wherein the semiconductor layer has a first side and a second side opposite the first side and adjacent to the substrate;
removing a portion of the semiconductor layer to form a cantilever extension;
forming a first electrical contact on the semiconductor layer;
forming a second electrical contact on the cantilever extension;
removing a portion of the semiconductor layer surrounding each pair of first and second electrical contacts to form a trench surrounding a semiconductor element made from the semiconductor layer, the semiconductor element having a substrate side in contact with the source substrate and a handle side opposite the substrate side;
providing a sacrificial layer covering the first and second electrical contacts and covering at least a portion of the handle side of the semiconductor element and filling a portion of the trench;
providing an interlayer over the sacrificial layer, the interlayer having different chemical selectivity than the sacrificial layer, wherein a portion of the interlayer contacts the source substrate at the base of the trench to form an anchor;
adhering the interlayer to a handle substrate;
removing the source substrate to expose the substrate side of the semiconductor element;
forming a tether bridging the exposed substrate side of the semiconductor element to the anchor; and
removing the sacrificial layer, thereby forming a printable semiconductor structure partially released from the handle substrate and physically secured to the anchor by the tether.
2. The method of claim 1 , wherein the sacrificial layer comprises a material selected from the group consisting of Si (1 1 1), InAlP, InP, GaAs, InGaAs, AlGaAs, GaSb, GaAlSb, AlSb, InSb, InGaAlSbAs, InAlSb, and InGaP.
3. The method of claim 1 , wherein the tether comprises a notch, the notch providing a point of fracture for a releasable micro object when retrieved by a transfer element.
4. The method of claim 1 , wherein the tether is a narrow shaped tether having a width of 10 μm to 40 μm.
5. The method of claim 1 , wherein forming the tether comprises:
forming a photo-sensitive layer on the exposed substrate side of the semiconductor element and the anchor;
selectively exposing portions of the photo-sensitive layer to an energized beam to alter solubility of the photo-sensitive layer to a photoresist developer; and
selectively removing portions of the photo-sensitive layer to define the tether comprising portions of the photo-sensitive layer.
6. The method of claim 1 , wherein the source substrate is a sapphire substrate.
7. The method of claim 1 , wherein the semiconductor layer comprises GaN and/or doped GaN.
8. The method of claim 1 , wherein the semiconductor layer comprises multiple sub-layers.
9. The method of claim 1 , wherein adhering the interlayer to a handle substrate comprises providing an adhesive layer on the interlayer and adhering the handle substrate to the adhesion layer.
10. The method of claim 1 , wherein removing the source substrate comprises removing the source substrate using laser ablation.
11. The method of claim 1 , comprising removing a portion of the semiconductor element to expose a portion of the first electrical contact.
12. The method of claim 1 , comprising forming protrusions on the first electrical contact.
13. The method of claim 1 , wherein the trench extends through the semiconductor layer to the source substrate.
14. The method of claim 1 , wherein the trench extends partially into the semiconductor layer such that a portion of the semiconductor layer forms an ablation layer between the semiconductor element and the source substrate.
15. The method of claim 1 , wherein the interlayer has a thermal conductivity greater than or equal to 1 W/mK.
16. The method of claim 1 , wherein the semiconductor element, the first electrical contact, and the second electrical contact form a diode, a laser, or a light-emitting diode, or
the method comprises providing one or more additional electrical contacts and the semiconductor element, the first electrical contact, and the second electrical contact and the one or more additional electrical contacts form a transistor.
17. The method of claim 1 , wherein the first electrical contact has a different thickness than the second electrical contact.
18. The method of claim 1 , wherein the first electrical contact and the second electrical contact extend to a common distance from a surface of the semiconductor element.
19. An inorganic semiconductor structure comprising:
a source substrate;
a semiconductor element surrounded by a trench, the semiconductor element having a substrate side in contact with the source substrate and a handle side opposite the substrate side;
a first metal contact in electrical contact with the semiconductor element on the handle side;
a second metal contact in electrical contact with the semiconductor element on the substrate side;
a sacrificial layer covering at least a portion of the semiconductor element and covering the first metal contact and filling a portion of the trench;
an interlayer formed over the sacrificial layer, wherein a portion of the interlayer contacts the source substrate at a base of the trench to form an anchor;
a handle substrate adhered to the interlayer, wherein at least a portion of the interlayer is between the handle substrate and the sacrificial layer; and
a tether bridging the substrate side of the semiconductor element to the anchor.