Metal routing with flexible space formed using self-aligned spacer patterning

1. A method comprising:

forming a first hard mask over a target layer;

forming a treatment mask comprising an opening;

performing a treatment on a first portion of the first hard mask to form a treated portion, with a second portion of the first hard mask left untreated as an untreated portion, wherein during the treatment, the first portion of the first hard mask is exposed through the opening in the treatment mask, and the second portion of the first hard mask is covered by the treatment mask;

etching to remove the untreated portion of the first hard mask using an etching chemical, wherein the treated portion is in physical contact with the etching chemical, and the treated portion remains after the etching; and

etching a layer underlying the first hard mask, wherein the treated portion of the first hard mask is used as a part of an etching mask in the etching.

2. The method of claim 1 further comprising forming a spacer on a sidewall of the treated portion of the first hard mask, wherein in the etching the layer underlying the first hard mask, both the spacer and the treated portion of the first hard mask are in combination used as the etching mask.

3. The method of claim 1 , wherein the treatment comprises a plasma treatment.

4. The method of claim 1 , wherein the treatment comprises an implantation.

5. The method of claim 1 further comprising performing a baking step after the treatment.

6. The method of claim 5 , wherein the baking step is performed at a temperature in a range between about 250° C. and about 500° C.

7. The method of claim 1 further comprising filling a conductive material into a trench formed by the etching the layer to form a conductive line.

8. The method of claim 1 further comprising, after the treatment, removing the treatment mask.

9. A method comprising:

forming a first hard mask;

forming a second hard mask over the first hard mask;

patterning the second hard mask to form a first opening therein;

modifying a first portion of the second hard mask to have properties different from a second portion of the second hard mask, wherein the modifying the first portion of the second hard mask comprises:

forming a treatment mask having a second opening therein, wherein the first portion of the second hard mask is exposed through the second opening; and

performing a treatment to modify the first portion of the second hard mask;

forming a spacer on a sidewall of the first portion of the second hard mask;

removing the second portion of the second hard mask, with the first portion of the second hard mask remaining after the removing; and

transferring patterns of the first portion of the second hard mask and the spacer into an underlying layer.

10. The method of claim 9 , wherein during the removing the second portion of the second hard mask, the first portion of the second hard mask is subject to a same etchant for etching the second portion.

11. The method of claim 9 , wherein the transferring the patterns comprises:

etching the first hard mask using the first portion of the second hard mask and the spacer in combination as an etching mask;

etching a dielectric layer underlying the first hard mask to form a trench; and

filling the trench to form a metal line.

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

forming a blanket spacer layer extending into the first opening; and

removing horizontal portions of the blanket spacer layer, with a portion of vertical portions of the blanket spacer layer being the spacer.

13. The method of claim 12 , wherein the spacer forms a ring encircling a middle portion of the first opening.

14. The method of claim 9 , wherein the treatment comprises an implantation with oxygen or boron being used as an implanted species.

15. The method of claim 9 , wherein the treatment comprises a plasma treatment using oxygen or carbon dioxide to generate plasma.

16. The method of claim 9 , further comprising performing a baking step after the treatment.

17. A method comprising:

forming a first opening, a second opening, a third opening, and a fourth opening in a hard mask;

forming a treatment mask covering a first portion of the hard mask between the first opening and the second opening, wherein a second portion of the hard mask between the third opening and the fourth opening is exposed through an opening in the treatment mask;

performing a treatment on the second portion of the hard mask;

removing the treatment mask;

forming spacers in the first opening, the second opening, the third opening, and the fourth opening;

exposing both the first portion and the second portion of the hard mask to an etchant, wherein the first portion is etched by the etchant, and the second portion has at least a bottom portion remaining; and

using the spacers and the second portion of the hard mask as an etching mask to etch an underlying layer.

18. The method of claim 17 , wherein the treatment comprises an implantation or a plasma treatment.

19. The method of claim 17 , wherein the hard mask comprises amorphous silicon, and the treatment is performed using an oxygen-containing species.

20. The method of claim 17 further comprising baking the treated hard mask.