Aluminum-beryllium alloys for air bridges
View Patent ↗A typical air bridge is an aluminum conductor suspended across an air-filled cavity to connect two components of an integrated circuit, two transistors for example. The air-filled cavity has a low dielectric constant which reduces cross-talk between neighboring conductors and improves speed and efficiency of the integrated circuit. However, current air bridges must be kept short because typical aluminum conductors sag too much. Accordingly, one embodiment of the invention forms air-bridge conductors from an aluminum-beryllium alloy, which enhances stiffness and ultimately provides a 40-percent improvement in air-bridge lengths.
1. A method of making an air bridge for an integrated circuit, the method comprising:
providing a supporting surface;
forming a conductive member from a metallic alloy, consisting essentially of aluminum, beryllium, and at least one of copper and titanium, on the supporting surface; and
removing at least a portion of the supporting surface to form a cavity underneath the conductive member.
2. A method of using an aluminum-beryllium alloy in forming an integrated circuit, the method comprising:
depositing the aluminum-beryllium alloy on a surface of the integrated circuit; and
patterning the deposited aluminum-beryllium alloy to define a conductor.
3. The method of claim 2 further comprising removing a portion of the surface underneath the conductor to form a cavity.
4. A method of fabricating a conductor comprising:
forming an aluminum-beryllium alloy; and
fabricating a conductor from the aluminum-beryllium alooy, wherein the conductor is a bridge spanning a cavity.
5. The method of claim 4 wherein forming the aluminum-beryllium alloy comprises sputter deposition.
6. The method of claim 5 wherein sputter deposition comprises first and second targets, the first target comprises beryllium and the second target comprises aluminum, aluminum-copper, aluminum-titanium or aluminum-copper-titanium.
7. The method of claim 4 wherein forming the aluminum-beryllium alloy comprises chemical vapor deposition.
8. The method of claim 4 wherein fabricating the conductor comprises patterning the aluminum-beryllium alloy with a photolithography process followed by an etch process.
9. The method of claim 4 wherein the aluminum-beryllium alloy is formed in a damascene trench and fabricating the conductor comprises removing portions of the alloy not contained within the trench.
10. The method of claim 4 wherein the cavity is formed after the aluminum-beryllium alloy is formed.
11. The method of claim 10 wherein the cavity is formed by removing a portion of the aluminum-beryllium alloy.
12. The method of claim 10 wherein the cavity is formed by removing material from under the aluminum-beryllium alloy.
13. The method of claim 12 wherein the material removed from under the aluminum-beryllium alloy comprises silicon nitride.
14. The method of claim 4 wherein the cavity is subsequently filled with a porous insulator material.
15. A method of fabricating a conductive element comprising:
depositing an aluminum-beryllium alloy above a removable region of material; and
removing the removable region of material.
16. The method of claim 15 wherein the aluminum-beryllium alloy is deposited using either a sputter deposition or a vapor deposition operation.
17. A method of forming a conductive bridge structure comprising:
depositing an aluminum-beryllium alloy;
forming a defined conductive path from the aluminum-beryllium alloy between first and second vertical support structures; and
creating a cavity under the conductive path between the first and second support structures.
18. The method of claim 17 wherein the aluminum-beryllium alloy comprises: 15-30% beryllium, 0-6% copper, 0-2titanium, and a remainder of aluminum and any impurities.
19. The method of claim 17 wherein the aluminum-beryllium alloy comprises 0.2-2% copper.
20. The method of claim 17 wherein the aluminum-beryllium alloy comprises 0.2-1% copper.
21. The method of claim 17 wherein the aluminum-beryllium alloy comprises less than 0.1% titanium.
22. The method of claim 17 wherein an unsupported length of the conductive path is greater than 1.2 millimeters, has a vertical thickness of 500 nanometers, and a maximum allowable vertical sag of 250 nanometers under its own weight.
23. The method of claim 17 wherein the aluminum-beryllium alloy comprises: 20-30% beryllium, 0.2-1% copper, less than 0.1% titanium, and a remainder of aluminum and any impurities.
24. The method of claim 17 wherein the aluminum-beryllium alloy comprises: 1-20% beryllium, 0-6% copper, 0-2% titanium, and a remainder of aluminum and any impurities.