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 forming an integrated circuit, comprising:
providing a substrate, wherein a temporary layer overlies the substrate and a photodefinable layer overlies the temporary layer;
forming a pattern in the photodefinable layer;
transferring the pattern to the temporary layer to form a plurality of spaced-apart placeholders in the temporary layer;
depositing a blanket layer of spacer material over the plurality of placeholders;
selectively removing the spacer material from horizontal surfaces to form a plurality of spacer loops formed of spacer material around sides of the spaced-apart placeholders;
selectively removing the placeholders relative to the spacer material to leave the plurality of spacer loops overlying the substrate;
etching the spacer loops to form a pattern of separated spacers, each spacer having two opposing sides extending a length of the spacer;
forming an other photodefinable layer around and on the same level as the separated spacers; and
patterning elongated photodefined features in the other photodefinable layer, wherein the photodefined features and the spacers are aligned such that each of the photodefined features contacts one side of each of the spacers without contacting the opposite side of the spacer.
2. The method of claim 1 , wherein a long side of each of the interconnect masking structures is substantially co-linear with a long side of each of the spacers.
3. The method of claim 1 , wherein the photodefinable layer comprises photoresist.
4. The method of claim 3 , wherein the photodefinable layer comprises positive photoresist.
5. The method of claim 4 , wherein the other photodefinable layer comprises photoresist.
6. The method of claim 5 , wherein the other photodefinable layer comprises negative photoresist.
7. The method of claim 5 , further comprising overdeveloping the photoresist.
8. The method of claim 5 , wherein the photoresist is compatible with 248 nm wavelength photolithography systems.
9. The method of claim 1 , wherein an other long side of the patterned interconnect masking structures opposite from the long side tapers toward an other side of the spacers opposite from the long side of each of the spacers.
10. The method of claim 1 , wherein the temporary layer comprises amorphous carbon.
11. The method of claim 10 , further comprising transferring the patterned photodefined features and the pattern of spacers to an additional mask layer underlying the pattern of spacers.
12. The method of claim 11 , wherein the additional mask layer comprises amorphous carbon.
13. The method of claim 1 , wherein forming a pattern in the photodefinable layer comprises exposing, developing and etching the photodefinable layer and subsequently isotropically etching the photodefinable layer.
14. The method of claim 1 , wherein a hard mask layer separates the temporary layer and the photodefinable layer.
15. The method of claim 14 , wherein the hard mask layer comprises a dielectric antireflective coating.
16. The method of claim 15 , wherein the dielectric antireflective coating comprises silicon oxynitride.
17. The method of claim 1 , wherein depositing a blanket layer of spacer material comprises depositing a layer of silicon by chemical vapor deposition.