Method to align mask patterns
Alignment tolerances between narrow mask lines, for forming interconnects in the array region of an integrated circuit, and wider mask lines, for forming interconnects in the periphery of the integrated circuit, are increased. The narrow mask lines are formed by pitch multiplication and the wider mask lines are formed by photolithography. The wider mask lines and are aligned so that one side of those lines is flush with or inset from a corresponding side of the narrow lines. Being wider, the opposite sides of the wider mask lines protrude beyond the corresponding opposite sides of the narrow mask lines. The wider mask lines are formed in negative photoresist having a height less than the height of the narrow mask lines. Advantageously, the narrow mask lines can prevent expansion of the mask lines in one direction, thus increasing alignment tolerances in that direction. In the other direction, use of photolithography and a shadowing effect caused by the relative heights of the photoresist and the narrow mask lines causes the wider mask lines to be formed with a rounded corner, thus increasing alignment tolerances in that direction by increasing the distance to a neighboring narrow mask line.
1. A method for integrated circuit fabrication, comprising:
forming a spacer over a substrate by performing pitch multiplication, wherein performing pitch multiplication comprises:
providing a mandrel over a substrate;
blanket depositing a layer of spacer material over the mandrel;
anisotropically etching the spacer material to form the spacer on a sidewall of the mandrel; and
selectively removing the mandrel; and
forming a photoresist line in contact with an end of the spacer, the photoresist line contacting only two faces of the spacer.
2. The method of claim 1 , wherein the photoresist line has a height less than a height of the spacer.
3. The method of claim 1 , wherein a long side of the spacer is flush with a long side of the photoresist line.
4. The method of claim 1 , wherein the photoresist line contacts an entire width of the end of the spacer.
5. The method of claim 1 , wherein the photoresist line contacts less than an entire width of the end of the spacer.
6. The method of claim 1 , wherein the spacer extends linearly between first and second spaced planes extending perpendicular to the spacer.
7. The method of claim 6 , wherein the photoresist line is linear between third and fourth spaced planes extending perpendicular to the photoresist line.
8. The method of claim 1 , wherein forming the photoresist line comprises:
depositing a layer of photoresist around the spacer line; and
photolithographically patterning the layer of photoresist to form the photoresist line.
9. The method of claim 8 , further comprising overdeveloping the photoresist line.
10. The method of claim 1 , wherein the photoresist line comprises negative photoresist.
11. The method of claim 1 , further comprising transferring a pattern formed by the spacer and the photoresist line into the substrate to define a conductive interconnect.
12. The method of claim 11 , further comprising transferring the pattern formed by the spacer and the photoresist line into a hard mask layer underlying the spacer and the photoresist line before transferring the pattern formed by the spacer and the photoresist line into the substrate.
13. The method of claim 12 , wherein the hard mask layer comprises amorphous carbon.
14. The method of claim 1 , wherein the mandrels comprise amorphous carbon.
15. A process for semiconductor fabrication, comprising:
forming a plurality of mandrels over a substrate;
blanket depositing a layer of spacer material over the mandrels;
anisotropically etching the spacer material to form spacers at sides of the mandrels;
forming a plurality of free-standing spacers by selectively removing the mandrels; and
forming a photodefinable layer around the free-standing spacers, the photodefinable layer having a thickness less than a height of the free-standing spacers.
16. The process of claim 15 , wherein the thickness of the photodefinable layer is about 80% or less of a height of the mask lines.
17. The process of claim 16 , wherein the thickness of the photodefinable layer is about 75-50% of the height of the mask lines.
18. The process of claim 15 , wherein forming the photodefinable layer comprises:
depositing photoresist; and
etching back the deposited photoresist.
19. The process of claim 15 , wherein forming the photodefinable layer comprises scan coating photoresist.
20. The process of claim 15 , wherein forming the plurality of mandrels comprises:
etching a pattern in a positive photoresist layer; and
transferring the pattern to an underlying layer to form the plurality of mandrels.
21. The process of claim 20 , wherein forming the photodefinable layer comprises depositing a layer of negative photoresist.
22. The process of claim 15 , wherein the spacers each form a loop around sidewalls of the mandrels, wherein forming the plurality of free-standing spacers comprises selectively removing ends of the loops.
23. The process of claim 22 , wherein selectively removing the ends of the loops comprises:
depositing a protective layer around and over the loops;
patterning the protective layer to expose the ends of the loops; and
selectively etching the ends of the loops relative to the protective layer.
24. The process of claim 23 , wherein selectively removing the ends of the loops is performed before selectively removing the mandrels.
25. The process of claim 15 , further comprising patterning a plurality of lines in the photoresist layer, each of the lines contacting a free-standing spacer.
26. The process of claim 25 , wherein each of the lines contacts only one long side of a free-standing spacer.
27. The process of claim 26 , wherein a critical dimension of the lines is larger than a critical dimension of the spacers.
28. The process of claim 15 , wherein a pitch of the plurality of free-standing spacers is less than 100 nm.