Self-aligned single dummy fin cut with tight pitch

1. A method for forming a semiconductor device, the method comprising:

forming a first spacer comprising a first material on a substrate;

depositing a block copolymer on a sidewall of the first spacer, the block copolymer assembling into alternating regions of a first polymer and a second polymer after a directed self-assembly (DSA);

removing the first polymer such that the second polymer defines a second spacer comprising a second material on the substrate, the second spacer adjacent to the first spacer; and

applying an etch process to the first spacer and the second spacer;

wherein the etch process removes the first spacer at a first etch rate;

wherein the etch process removes the second spacer at a second etch rate;

wherein the first etch rate is different than the second etch rate;

wherein forming the first spacer further comprises;

forming a sacrificial material layer overlying the substrate;

depositing a hard mask layer on top of the substrate, the hard mask layer between the substrate and the sacrificial material layer;

removing portions of the sacrificial material layer to form a sacrificial mandrel, the sacrificial mandrel having sidewalls;

forming the first spacer adjacent to the sidewalls of the sacrificial mandrel; and removing the sacrificial mandrel.

2. The method of claim 1 , further comprising: depositing a conformal spacer layer over the mandrel; and removing portions of the conformal spacer layer, the remaining portions of the conformal spacer layer defining the first spacer.

3. The method of claim 1 , wherein the sacrificial material layer comprises a silicon nitride (SiN), and wherein the hard mask layer is amorphous carbon (aC).

4. The method of claim 1 , further comprising:

treating the sidewall of the first spacer with a precursor polymer; and

infiltrating the second polymer with a metal oxide using a sequential infiltration synthesis (SIS) process.

5. The method of claim 4 , wherein the DSA operation further comprises annealing the block copolymer using nitrogen carrier gas at a temperature of 200 to 290 degrees Celsius.

6. The method of claim 4 , wherein the block copolymer is polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA), the first polymer is PS, the second polymer is PMMA, and the precursor polymer is PS-OH, and wherein infiltrating the PMMA with a metal oxide comprises converting the PMMA to aluminum (Al 2 O 3 ).

7. The method of claim 1 , further comprising:

forming a first set of spacers of the first material on the substrate;

forming a second set of spacers of the second material on the substrate;

forming a mask material layer on the first set of spacers and on the second set of spacers;

forming an opening in the mask material layer selective to the first material, the second material, and the hard mask layer, the opening having first and second sidewalls;

positioning the first sidewall of the opening over a first spacer of the second set of spacers, the first spacer of the second set of spacers adjacent to the first spacer of the first set of spacers;

positioning the second sidewall of the opening over a second spacer of the second set of spacers, the second spacer of the second set of spacers opposite to the first spacer of the second set of spacers and adjacent to the first spacer of the first set of spacers; and

removing the first spacer of the first set of spacers selective to the second material and the hard mask layer.

8. The method of claim 7 , further comprising:

etching the hard mask layer to expose portions of the substrate;

removing exposed portions of the substrate to form a first fin and a second fin; and

forming a gate stack over a channel region of the first fin and the second fin.

9. A method for forming a semiconductor device, the method comprising:

forming a first spacer, a second spacer, and a third spacer on a substrate, the first spacer and the third spacer comprising a first material and the second spacer comprising a second material, the second spacer arranged between the first spacer and the third spacer;

applying an etch process to the first spacer, the second spacer, and the third spacer;

wherein the etch process removes the first spacer and the third spacer at a first etch rate;

wherein the etch process removes the second spacer at a second etch rate;

wherein the first etch rate is different than the second etch rate;

wherein the etch process removes the second spacer to expose a portion of the substrate.

10. The method of claim 9 , wherein forming the first and third spacers includes:

forming a sacrificial mandrel having a first and a second sidewall on a substrate;

forming the first spacer adjacent to the first sidewall of the sacrificial mandrel;

forming the second spacer adjacent to the second sidewall of the sacrificial mandrel; and

removing the sacrificial mandrel to expose portions of the substrate.

11. The method of claim 9 , wherein forming the second spacer includes:

depositing a block copolymer layer adjacent to the spacers on the substrate;

annealing to form a first material region and a second material region in the block copolymer layer;

performing an infiltration process such the second material region includes a metallic material; and

removing the first material region.

12. The method of claim 9 , wherein the first material and the second material are not the same material.

13. The method of claim 9 , further comprising:

forming a mask material layer on the three spacers;

forming an opening in the mask material layer, the opening having first and second sidewall s;

positioning the first sidewall between the first spacer and the second spacer; and

positioning the second sidewall over the substrate on a first side of the third spacer furthest from the second spacer, such that the opening extends beyond the first side and a second side of the third spacer;

wherein the opening is formed selective to the first material, the second material, and the substrate;

wherein removing the second spacer comprises an oxide etch selective to the first material and the substrate.