Single-crystal hexagonal boron nitride layer and method forming same

1. A method comprising:

depositing a copper layer over a first substrate, wherein the copper layer is deposited to have a polycrystalline structure;

annealing the copper layer, wherein after the annealing, the polycrystalline structure is converted into a single-crystalline structure;

depositing a hexagonal boron nitride (hBN) film on the copper layer; and

removing the hBN film from the copper layer.

2. The method of claim 1 , wherein the copper layer is deposited to have a (iii) surface plane.

3. The method of claim 1 , wherein the annealing is performed with the copper layer facing down, and with the first substrate being over the copper layer.

4. The method of claim 1 , wherein the removing the hBN film from the copper layer comprises:

forming a protection layer over and contacting the hBN film;

forming a thermal release tape on the protection layer; and

separating the hBN film from the copper layer.

5. The method of claim 4 further comprising, after the hBN film is separated from the copper layer, adhering the hBN film to a second substrate.

6. The method of claim 5 further comprising:

depositing or transferring a Transition Metal Dichalcogenide (TMD) layer over the hBN film that is on the second substrate; and

transferring an additional hBN film over the TMD layer.

7. The method of claim 4 , wherein the hBN film is separated from the copper layer through electrochemical delamination.

8. The method of claim 1 , wherein the depositing the copper layer comprises sputtering copper from a copper target, with the sputtered copper being deposited on the first substrate.

9. The method of claim 1 , wherein the annealing the copper layer is performed at a temperature in a range between 500° C. and 1,100° C.

10. A method comprising:

forming a single-crystalline copper layer on a first substrate;

depositing a first single-crystalline hexagonal boron nitride (hBN) film over the single-crystalline copper layer;

transferring the first single-crystalline hBN film onto a second substrate;

forming a Transition Metal Dichalcogenide (TMD) layer over the first single-crystalline hBN film;

transferring a second single-crystalline hBN film over the TMD layer; and

forming a transistor comprising the TMD layer as a channel.

11. The method of claim 9 , wherein the forming the transistor comprises:

forming a source/drain region over and contacting the second single-crystalline hBN film, wherein the source/drain region is physically separated from the TMD layer by the second single-crystalline hBN film.

12. The method of claim 9 , wherein the forming the transistor comprises:

forming a source/drain region having a first sidewall contacting a second sidewall of the second single-crystalline hBN film and a third sidewall of the TMD layer.

13. The method of claim 9 , wherein the depositing the first single-crystalline hBN film is self-stopping, and the first single-crystalline hBN film is a mono-layer film.

14. The method of claim 9 , wherein the forming the single-crystalline copper layer comprises:

depositing a polycrystalline copper layer; and

performing an annealing process to convert the polycrystalline copper layer into the single-crystalline copper layer.

15. The method of claim 11 , wherein the annealing process is performed at a temperature in a range between 500° C. and 1,100° C.

16. A method comprising:

depositing a first single-crystalline hexagonal boron nitride (hBN) film over a copper layer, wherein the copper layer has a single-crystalline structure, with the first single-crystalline hBN film being deposited on a (iii) surface of the copper layer;

forming a protection layer over and contacting the first single-crystalline hBN film;

performing an electrochemical delamination process to separate the first single-crystalline hBN film and the protection layer from the copper layer;

adhering the first single-crystalline hBN film and the protection layer to a substrate, with the first single-crystalline hBN film contacting the substrate; and

removing the protection layer from the first single-crystalline hBN film.

17. The method of claim 16 , wherein the copper layer has a thickness in a range between 400 nm and 600 nm.

18. The method of claim 15 further comprising:

depositing a polycrystalline copper layer; and

performing an annealing process to convert the polycrystalline copper layer into the copper layer having the single-crystalline structure.

19. The method of claim 18 , wherein the annealing process is performed at a temperature in a range between 500° C. and 1,100° C.

20. The method of claim 15 , wherein the first single-crystalline hBN film is a mono-layer hBN film.