Metal line with increased inter-metal breakdown voltage

1. A method of forming an integrated circuit comprising:

forming a first metal layer;

subsequently forming a dielectric layer over the first metal layer;

subsequently forming a wide trench having a width W 1 and forming narrow trenches having a width W 2 that is less than W 1 in the dielectric layer, the wide trench extending deeper in outer regions than in a central region;

subsequently performing a trench modification step that changes the width of the wide trench and reduces a depth difference between the outer regions and the central region of the wide trench; and

subsequently depositing a second metal layer that fills the wide trench and the narrow trenches.

2. The method of claim 1 wherein the trench modification step includes deposition of a filler layer in the wide trench and subsequent etching back of the filler layer thereby reducing the width of the wide trench to W 3 , where W 3 is less than W 1 , and thereby partially filling outer regions of the wide trench with the filler layer.

3. The method of claim 2 wherein the deposition of the filler layer in the wide trench and the subsequent etching back of the filler layer reduces the depth difference between the outer regions and the central region of the wide trench to about zero.

4. The method of claim 2 wherein the deposition of the filler layer does not deposit significant filler layer material in the narrow trenches.

5. The method of claim 4 wherein the filler layer is formed of silicon oxide deposited by chemical vapor deposition using silane (SiH4).

6. The method of claim 5 wherein the etching back of the filler layer removes substantially all of the filler layer from the central region of the wide trench and removes substantially all of the filler layer from over the dielectric layer.

7. The method of claim 6 wherein the etching back includes an anisotropic etching step that exposes vias in the central region of the wide trench.

8. The method of claim 1 wherein the trench modification step includes slimming of etch mask portions and subsequent extending of the wide trench to have a width W 4 in an upper portion, where W 4 is greater than W 1 .

9. The method of claim 8 wherein the wide trench is formed having a width W 1 by applying a set of etch conditions and the wide trench is extended by applying the set of etch conditions.

10. The method of claim 9 wherein the set of etch conditions provide a first etch rate in the outer regions when forming the wide trench having a width W 1 and subsequently provide a second etch rate in the outer regions when extending the wide trench, the second etch rate being less than the first etch rate.

11. The method of claim 10 wherein, when forming the wide trench having a width W 1 and subsequently when extending the wide trench, the set of etch conditions provide substantially the second etch rate in the central region.

12. The method of claim 9 wherein the set of etch conditions produces etch byproducts at exposed regions of the dielectric layer, the etch byproducts distributed unevenly within the wide trench, and inhibiting subsequent etching unevenly within the wide trench.

13. The method of claim 1 further comprising subsequently removing excess second metal layer to form bit lines of a NAND flash memory in the narrow trenches and to form a wide conductive line in the wide trench.

14. An integrated circuit comprising:

a first layer of metal conductive lines;

a dielectric layer overlying the first layer of metal conductive lines, the dielectric layer having narrow trenches and a wide trench, the wide trench having stepped sidewalls and extending deeper in edge regions than in a central region; and

a wide metal line formed in the wide trench.

15. The integrated circuit of claim 14 wherein each of the narrow trenches has stepped sidewalls.

16. The integrated circuit of claim 14 wherein each of the narrow trenches contains a bit line of a NAND flash memory.

17. An integrated circuit comprising:

a first layer of metal conductive lines;

a dielectric layer overlying the first layer of metal conductive lines, the dielectric layer having narrow trenches and a wide trench;

a wide metal line formed in the wide trench, the wide metal line lying in direct physical contact with the dielectric layer in a central region; and

filler portions in edge regions of the wide trench located on either side of the central region, the filler portions extending under the wide metal line in the edge regions.

18. The integrated circuit of claim 17 wherein the filler portions extend between sidewalls of the wide trench and sides of the wide metal line.

19. The integrated circuit of claim 17 wherein the wide metal line has substantially same vertical distance from the first layer of metal conductive lines in the edge regions and in the central region.

20. The integrated circuit of claim 17 wherein the integrated circuit is a NAND flash memory and the narrow trenches contain bit lines.