Air gap for dual damascene applications
An air gap structure and formation method for substantially reducing capacitance in a dual damascene based interconnect structure is disclosed. The air gap extends above, and may also additionally extend below, the damascene interconnects desired to be isolated thus minimizing fringing fields between the lines. Multiple levels of the integrated air gap structure can be fabricated to accommodate multiple metal levels.
1. A method for forming an air gap structure in an integrated circuit, the method comprising:
forming a device layer;
forming a dual damascene opening over the device layer including first and second patterned openings in at least one first dielectric layer;
forming a dual damascene conductive pattern of conductive lines by filling the first and second patterned openings with at least one conductive material;
forming a adjustable-depth trench between adjacent conductive lines in said dual damascene conductive pattern using the dual damascene conductive structure as a hard mask; and
forming a second dielectric layer over the trench to encapsulate said trench and form at least one air gap therein.
2. The method of claim 1 in which forming an adjustable-depth trench between the said dual damascene conductive pattern comprises forming the trench at least down to a top surface of said device layer.
3. The method of claim 1 in which forming said air gap comprises forming at least an air gap extending above a top surface of said dual damascene conductive pattern.
4. The method of claim 1 in which forming said air gap comprises forming at least an air gap extending down to a top surface of said device layer.
5. The method of claim 1 further comprising forming an etch stop layer underneath said first dielectric layer.
6. The method of claim 1 wherein said first dielectric layer includes a via dielectric layer and a separate line dielectric layer, and further including a step of forming an anti-reflecting layer on a top surface of the said separate line dielectric layer.
7. The method of claim 1 further comprising forming a barrier layer in said dual damascene opening.
8. The method of claim 1 further comprising forming a seed layer in said dual damascene opening.
9. The method of claim 1 in which said conductive material includes a copper based layer, said copper based layer extending to a first depth in said first patterned opening, and to a second depth in said second patterned opening which extends to said device layer.
10. The method of claim 1 further comprising chemical-mechanical polishing of said conductive layer.
11. The method of claim 1 in which forming said adjustable-depth trench between said dual damascene conductive pattern comprises forming a trench extending beyond the surface of the device layer.
12. The method of claim 1 in which forming said second dielectric layer comprises forming a dielectric layer selected from a group including SiO2, USG, PSG, BPSG, and FSG.
13. The method of claim 1 in which forming said second dielectric layer comprises forming a dielectric layer to a thickness of about 1000 to 10000 Angstroms.
14. The method of claim 1 further comprising forming a resist layer on a top surface of said at least one first dielectric layer.
15. The method of claim 14 further comprising patterning said resist layer.
16. The method for forming an air gap structure in an integrated circuit, the method comprising:
forming a device layer; and
forming at least a first dielectric layer on the device layer; and
patterning said at least first dielectric layer to form first openings therein; and
forming a copper-based layer in a dual damascene process on the at least first dielectric layer and so as to fill said first openings therein; and
removing a part of said copper-based layer to form an interconnect structure of copper conductive lines; and
forming a second opening between two adjacent copper conductive lines in said interconnect structure using said interconnect structure as a mask; and
forming a second dielectric layer over said second opening to form at least one air gap between said two adjacent copper conductive lines and extending down to a top surface of said device layer;
wherein said at least one air gap is formed without using a photoresist-based mask after said interconnect structure of copper conductive lines is completed.
17. The method of claim 16 , wherein said first openings include both damascene vias and damascene trenches.
18. The method of claim 16 in which forming a second opening between two adjacent copper conductive lines comprises forming the opening at least down to a top surface of said device layer.
19. The method of claim 16 in which forming said air gap comprises forming at least an air gap extending above a top surface of said dual damascene conductive pattern.
20. The method of forming an air gap structure in an integrated circuit, the method comprising:
forming a device layer;
forming a dual damascene opening over the device layer including first and second patterned openings in a first dielectric material;
forming a dual damascene conductive pattern of conductive lines by filling the first and second patterned openings with a conductive material;
using a timed etch process that has predominantly an anisotropic behavior to form an adjustable depth trench between adjacent conductive lines in said dual damascene conductive pattern; and
forming a second dielectric material over said adjustable depth trench to encapsulate said adjustable-depth trench and form at least one air gap therein;
wherein a size of said at least one air gap is controlled by controlling a size of said adjustable depth trench and a deposition coverage characteristic of said second dielectric material.
21. The method of claim 20 , wherein said second dielectric material has a deposition coverage characteristic that is substantially conformal.
22. The method of claim 20 , wherein said first dielectric material includes a first dielectric layer and a second dielectric layer.
23. The method of claim 20 , wherein said dual damascene opening is formed in a first etching operation that etches through both said first dielectric material and said second dielectric material, and a second etching operation that only etches said second dielectric layer.
24. The method of claim 20 , wherein said air gap comprises at least an air gap extending above a top surface of said dual damascene conductive pattern.
25. The method of claim 24 , wherein said air gap comprises at least an air gap extending down to a top surface of the device layer.