Method for depositing a group III nitride semiconductor film
A method for depositing a Group III nitride semiconductor film on a substrate is provided that comprises: providing a sapphire substrate; placing the substrate in a vacuum chamber; conditioning a surface of the substrate by etching and providing a conditioned surface; holding the substrate away from a substrate facing surface of a heater by a predetermined distance; heating the substrate to a temperature by using the heater whilst the substrate is held away from the substrate facing surface of the heater, and depositing a Group III nitride semiconductor film onto the conditioned surface of the substrate by a physical vapour deposition method whilst the substrate is held away from the substrate facing surface of the heater and forming an epitaxial Group III nitride semiconductor film with N-face polarity on the conditioned surface of the substrate.
1. A method for depositing a Group III nitride semiconductor film on a substrate, comprising:
providing a sapphire substrate;
placing the substrate in a vacuum chamber;
conditioning a surface of the substrate by etching and providing a conditioned surface;
holding the substrate away from a substrate facing surface of a heater by a predetermined distance;
heating the substrate to a temperature T 1 by using the heater whilst the substrate is held away from the substrate facing surface of the heater;
depositing a Group III nitride semiconductor film onto the conditioned surface of the substrate by a physical vapour deposition method whilst the substrate is held away from the substrate facing surface of the heater and forming an epitaxial Group III nitride semiconductor film with N-face polarity on the conditioned surface of the substrate.
2. The method according to claim 1 , wherein the conditioning the surface of the substrate comprises plasma soft-etching the surface under vacuum.
3. The method according to claim 2 , wherein the plasma soft-etching comprises heating the substrate to a temperature T 2 , introducing Ar gas into the vacuum chamber and subjecting the surface of the substrate to a plasma.
4. The method according to claim 3 , wherein T 2 is 35° C. to 70° C.
5. The method according to claim 1 , wherein the plasma soft-etching is carried out at a pressure of 2.10 −4 mbar to 8.10 −4 mbar with a RF plasma comprising Ar + ions.
6. The method according to claim 2 , wherein T 2 <T 1 .
7. The method according to claim 2 , wherein during the plasma soft-etching the substrate is held away from the substrate facing surface of the heater.
8. The method according to claim 1 , wherein the conditioning the surface of the substrate comprises chemical etching the surface.
9. The method according to claim 1 , wherein the etching comprises preferentially removing chemically bound oxygen from the substrate.
10. The method according to claim 1 , wherein after the etching the conditioned surface is Al-terminated.
11. The method according to claim 1 , further comprising subjecting the conditioned surface to a nitrogen flow in the vacuum chamber after the conditioning.
12. The method according to claim 1 , wherein T 1 lies in the range 650° C. to 800° C.
13. The method according to claim 1 , further comprising flowing Argon gas over the substrate whilst the substrate is heated up to the temperature T 1 .
14. The method according to claim 1 , wherein the conditioning is carried out in a first vacuum chamber and the depositing is carried out in a second vacuum chamber.
15. The method according to claim 1 , further comprising reducing the pressure in the vacuum chamber after the conditioning.
16. The method according to claim 1 , wherein the Group III nitride semiconductor film is deposited onto the conditioned surface of the substrate by reactive sputtering.
17. The method according to claim 16 , wherein a DC power of 1.5 to 3 kW is used to sputter the Group III nitride semi-conductor film onto the conditioned surface.
18. The method according to claim 1 , wherein the Group III nitride semiconductor film is deposited onto the conditioned surface of the substrate by RF sputtering.
19. The method according to claim 1 , further comprising depositing a seed layer on the conditioned surface in a N 2 /Ar atmosphere, wherein a ratio of N 2 to Ar is greater than 3, and depositing the film onto the seed layer in a in a N 2 /Ar atmosphere, wherein the ratio of N 2 to Ar is less than 3.
20. The method according to claim 1 , further comprising actively cooling the substrate after depositing the Group III nitride film.
21. The method according to claim 1 , wherein the Group III nitride film is AlN.
22. The method according to claim 1 , further comprising sputtering a further Group III nitride semiconductor film onto the epitaxial Group III nitride semiconductor film, the further Group III nitride semiconductor film having Group III-face polarity.