Self-aligned multi-patterning for advanced critical dimension contacts

1. A method of forming patterned features on a substrate, the method comprising:

forming a first sacrificial structural layer of core material on the substrate;

patterning the first sacrificial structural layer to form a plurality of evenly spaced cores from the first sacrificial layer such that the plurality of cores are arranged in a pattern comprising a plurality of squares with each square in the plurality of squares being defined by four adjacent cores, wherein a side of each square in the pattern has a length equal to a first pitch;

forming a conformal layer of spacer material over the cores and exposed substrate leaving a dimple at a center of each square in the pattern;

anisotropically etching the conformal layer to expose the cores and a region of the substrate at the center of each square in the pattern; and

removing the cores.

2. The method of claim 1 further comprising the steps of:

depositing a second sacrificial structural layer;

partially etching the second sacrificial structural layer; and

etching the spacer material leaving a plurality of cores, comprising a core at each corner of the square and a core at a center of the square.

3. The method of claim 1 wherein a diameter of one of the cores at the corner of the square is about one quarter of the first pitch.

4. The method of claim 1 wherein a thickness of the conformal layer is between about 40% and about 52% of the first pitch.

5. The method of claim 1 wherein a thickness of the conformal layer is between about 43% and about 49% of the first pitch.

6. The method of claim 1 wherein the core material comprises hydrogenated amorphous carbon having an atomic composition of between about 10 percent hydrogen to about 60 percent hydrogen.

7. The method of claim 1 wherein the spacer material comprises silicon nitride.

8. A method of patterning a substrate having a first sacrificial structural layer of core material using a single high-resolution photomask, the method comprising:

depositing a layer of photoresist over the first sacrificial structural layer;

patterning the layer of photoresist by exposing the layer of photoresist to radiation through the single high-resolution photomask and developing the layer of photoresist to form a first pattern of photoresist features, wherein the first pattern comprises a two-dimensional array which repeats in each dimension with a first pitch;

transferring the first pattern into the first sacrificial structural layer to form a first two-dimensional array of cores from the first sacrificial structural layer comprising a first plurality of cores arranged in a first square pattern including a first plurality of squares where each square in the first plurality of squares is defined by four adjacent cores and has a side length of about the first pitch;

forming a first conformal layer of spacer material over the first plurality of cores and exposed substrate leaving a first dimple at a center of each square in the first square pattern;

anisotropically etching the first conformal layer to expose the first plurality of cores and a region of the substrate at the center of each square in the first square pattern;

removing the first two-dimensional array of cores;

depositing a second sacrificial structural layer;

partially etching the second sacrificial structural layer to reveal spacer material;

etching the spacer material leaving a second two-dimensional array of cores formed from the spacer material comprising a second plurality of cores arranged in a second square pattern having twice the density of the first square pattern and including a second plurality of squares where each square in the second plurality of squares is defined by four adjacent cores and, has a side length of about the first pitch divided by the square root of two;

forming a second conformal layer of spacer material over the second plurality of cores and exposed substrate leaving a second dimple at a center of each square in the second square pattern;

anisotropically etching the second conformal layer to expose the second plurality of cores and a region of the substrate at the center of square in the second square pattern; and

removing the second two-dimensional array of cores.

9. The method of claim 8 further comprising:

depositing a metal layer; and

partially removing the metal layer to form a two-dimensional array of vias having four times the density of the first two-dimensional array of cores.

10. The method of claim 8 wherein a diameter of one of the cores in the first two-dimensional array of cores is about one quarter of the first pitch.

11. The method of claim 8 wherein a thickness of the first conformal layer is between about 40% and about 52% of the first pitch.

12. The method of claim 8 wherein a thickness of the first conformal layer is between about 43% and about 49% of the first pitch.

13. The method of claim 8 wherein a thickness of the second conformal layer is between about 20% and about 30% of the first pitch.

14. The method of claim 8 wherein a thickness of the second conformal layer is between about 22% and about 28% of the first pitch.

15. The method of claim 8 wherein the core material comprises hydrogenated amorphous carbon having an atomic composition of between about 10 percent hydrogen to about 60 percent hydrogen.

16. The method of claim 8 wherein the spacer material comprises silicon and at least one of oxygen and nitrogen.