Degradable neutral layers for block copolymer lithography applications
Polymer films comprising crosslinked random copolymers and methods for making the films are provided. Also provided are polymer films comprising random copolymers that are covalently linked to an underlying substrate. The polymer films can be incorporated into structures in which the films are employed as surface-modifying layers for domain-forming block copolymers and the structures can be used for pattern transfer applications via block copolymer lithography. The crosslinks between the random copolymer chains in the polymer films or the links between the random copolymer chains and the substrate surface are characterized in that they can be cleaved under relatively mild conditions.
1. A method of forming a self-assembled block copolymer film, the method comprising:
forming a crosslinked copolymer film on a substrate surface, the crosslinked copolymer film comprising crosslinked random copolymer chains, wherein the crosslinks comprise photocleavable junctions or mild acid-cleavable junctions;
depositing a domain-forming block copolymer over the crosslinked copolymer film; and
subjecting the domain-forming block copolymer to conditions that induce the block copolymer to self-assemble into a pattern of block copolymer domains.
2. The method of claim 1 , wherein the crosslinked copolymer film provides a neutral layer, such that the block copolymer domains are vertically oriented.
3. The method of claim 2 , further comprising selectively removing one or more of the block copolymer domains and the portions of the crosslinked copolymer film underlying said domains, such that a mask pattern is formed over the substrate.
4. The method of claim 3 , further comprising transferring the mask pattern to the substrate.
5. The method of claim 3 , wherein the crosslinks comprise the photocleavable junctions and further wherein the step of selectively removing the portions of the crosslinked copolymer film underlying said domains comprises exposing said portions to radiation having wavelengths that cleave the photocleavable junctions in the crosslinks, such that the random copolymer chains are uncrosslinked, and removing the uncrosslinked random copolymer chains from the substrate surface.
6. The method of claim 5 , wherein the photocleavable junctions are UV-cleavable.
7. The method of claim 6 , wherein the photocleavable junctions are provided by 2-nitrobenyl groups.
8. The method of claim 6 , wherein the photocleavable junctions are reversibly photocrosslinkable junctions.
9. The method of claim 8 , wherein the reversibly photocrosslinkable junctions are provided by reversibly photodimerizable coumarin groups.
10. The method of claim 3 , wherein the step of selectively removing the portions of the crosslinked copolymer film underlying said domains comprises exposing said portions to a mild acid that cleaves mild acid-cleavable junctions in the crosslinks, such that the random copolymer chains are uncrosslinked, and removing the uncrosslinked random copolymer chains from the substrate surface.
11. The method of claim 10 , wherein the mild acid-cleavable junctions are provided by acetal groups.
12. The method of claim 1 , wherein forming the crosslinked copolymer film on the substrate surface comprises:
depositing a coating comprising the random copolymer chains onto a substrate surface, wherein the random copolymer chains comprise comonomers comprising crosslinkable functional groups; and
subjecting the coating to conditions that induce crosslinking reactions between the crosslinkable functional groups to form the crosslinks.
13. The method of claim 12 , wherein the photocleavable or mild acid-cleavable junctions are formed by the crosslinking reactions.
14. The method of claim 12 , wherein the comonomers comprising the crosslinkable functional groups further comprise the photocleavable or mild acid-cleavable junctions.
15. The method of claim 12 , wherein forming the crosslinked copolymer film on the substrate surface comprises:
depositing a coating comprising a crosslinking agent and the random copolymer chains onto a substrate surface, wherein the random copolymer chains comprise comonomers comprising crosslinkable functional groups; and
subjecting the coating to conditions that induce crosslinking reactions between the crosslinking agent and the crosslinkable functional groups to form the crosslinks.
16. A method of forming a self-assembled block copolymer film, the method comprising:
forming a copolymer film on a substrate surface, the copolymer film comprising random copolymer chains, wherein the random copolymer chains are bonded to the surface at multiple points by surface links and further wherein the surface links comprise photocleavable junctions or mild acid-cleavable junctions;
depositing a domain-forming block copolymer over the surface-linked copolymer film; and
subjecting the domain-forming block copolymer to conditions that induce the block copolymer to self-assemble into a pattern of block copolymer domains.
17. The method of claim 16 , wherein the surface-linked copolymer film provides a neutral layer, such that the block copolymer domains are vertically oriented.
18. The method of claim 17 , further comprising selectively removing one or more of the block copolymer domains and the portions of the surface-linked copolymer film underlying said domains, such that a mask pattern is formed over the substrate.
19. The method of claim 16 , wherein the crosslinks comprise the mild acid-cleavable junctions and further wherein the step of selectively removing the portions of the surface-linked copolymer film underlying said domains comprises exposing said portions to a mild acid that cleaves the mild acid-cleavable junctions in the surface links, such that the random copolymer chains are unlinked from the substrate surface, and removing the unlinked random copolymer chains from the substrate surface.
20. The method of claim 19 , wherein the mild acid-cleavable junctions are provided by acetal groups.
21. The method of claim 5 , wherein the radiation has wavelengths shorter than 254 nm that cleaves the photocleavable junctions.
22. The method of claim 10 , wherein the mild acid has a pKa higher than that of trifluoroacetic acid.
23. The method of claim 19 , wherein the mild acid has a pKa higher than that of trifluoroacetic acid.