Block copolymer materials for directed assembly of thin films
Provided herein are methods of formulating and engineering block copolymer (BCP) systems for directed self-assembly (DSA) processes. In some embodiments, the methods involve engineering a BCP material based on the interaction parameter (χ) of the material and the surface and/or interaction energies of its constituent blocks. Also provided are novel block BCP materials that can be used in DSA techniques. In some embodiments, the BCP systems described herein have micro-phase separating blocks, with at least one block including multiple types of repeat units. Also provided are structures formed by DSA, including structures having a sub-20 nm dimension. Applications included nanolithography for semiconductor devices, fabrication of cell-based assays, nanoprinting, photovoltaic cells, and surface-conduction electron-emitter displays.
1. A method of formulating a block copolymer material for directed assembly, comprising:
forming a modified block copolymer including an A block and a B′ block, wherein the B′ block is a B-C statistical or random copolymer,
wherein the interaction parameter (χ) of the modified block copolymer is larger than that of PS-b-PMMA at a particular temperature of assembly and wherein surface or interfacial energies of the A and B′ blocks are commensurate with each other such that the BCP system can assemble in a thin film with non-preferential wetting of domains of the A and B′ blocks at the surface or interface of the thin film.
2. The method of claim 1 , wherein a B block of an A-b-B block copolymer is modified to form a A-b-B′ block copolymer.
3. The method of claim 1 , wherein the B′ block includes B and C monomers and wherein the C monomers are B monomers that are modified with a functional group.
4. The method of claim 1 , wherein the difference in surface energies between the A and B′ blocks is no more than the difference in surface energies of PS and PMMA at a particular temperature of assembly.
5. The method of claim 1 , wherein the difference in interfacial energies between the A and B′ blocks is no more than the difference in interfacial energies of PS and PMMA at a particular temperature of assembly.
6. The method of claim 1 , further comprising forming the B′ random or statistical polymer prior to forming the modified block copolymer.
7. The method of claim 1 , further comprising partially epoxidizing a B homopolymer or a B block of a A-b-B block copolymer to form the B′ block.
8. The method of claim 1 , wherein the A block is a homopolymer.
9. The method of claim 1 , wherein the A block is a random or statistical polymer.
10. The method of claim 1 , further comprising directing the assembly of a thin film of the modified block copolymer.
11. The method of claim 1 , further comprising one or more of partial sulfonation, hydrogenation, fluorination, polyhedral oligomeric silsesquioxanes attachment, or liquid crystal attachment of a B homopolymer or a B block of a A-b-B block copolymer to form the B′ block.
12. The method of claim 1 , wherein the modified block copolymer has at least three blocks.
13. The method of claim 1 , wherein the modified block copolymer is a poly(styrene-b-isoprene) block copolymer, wherein about 50% to about 90% of the polyisoprene block is modified with epoxy functional groups.
14. The method of claim 13 , wherein about 70% to 80% of the polyisoprene block is modified with epoxy functional groups.
15. The method of claim 1 , wherein C is a polymer having a surface energy such that the surface energy of the A block is between that of a B polymer and C.
16. The method of claim 1 , further comprising experimentally determining the surface or interfacial energy of at least one of the A, B and C polymers.