Orientation Control in Thin Films of a High-χ Block Copolymer with a Surface Active Embedded Neutral Layer

Abstract

Directed self-assembly (DSA) of block copolymers (BCPs) is an attractive advanced patterning technology being considered for future integrated circuit manufacturing. By controlling interfacial interactions, self-assembled microdomains in thin films of polystyrene-block-poly(methyl methacrylate), PS-b-PMMA, can be oriented perpendicular to surfaces to form line/space or hole patterns. However, its relatively weak Flory interaction parameter, χ, limits its capability to pattern sub-10 nm features. Many BCPs with higher interaction parameters are capable of forming smaller features, but these "high-χ" BCPs typically have an imbalance in surface energy between the respective blocks that make it difficult to achieve the required perpendicular orientation. To address this challenge, we devised a polymeric surface active additive mixed into the BCP solution, referred to as an embedded neutral layer (ENL), which segregates to the top of the BCP film during casting and annealing and balances the surface tensions at the top of the thin film. The additive comprises a second BCP with a "neutral block" designed to provide matched surface tensions with the respective polymers of the main BCP and a "surface anchoring block" with very low surface energy that drives the material to the air interface during spin-casting and annealing. The surface anchoring block allows the film to be annealed above the glass transition temperature of the two materials without intermixing of the two components. DSA was also demonstrated with this embedded neutral top layer formulation on a chemical patterned template using a single step coat and simple thermal annealing. This ENL technology holds promise to enable the use of high-χ BCPs in advanced patterning applications.

Thermal Approaches to Perpendicular Block Copolymer Microdomains in Thin Films: A Review and Appraisal

“…Interestingly, the first demonstration of fluorinated additives in BCP thin films used PS‐ b ‐PMMA as the matrix (presumably due to the low annealing temperature which causes a larger mismatch in the γ of PS and PMMA), using P(S‐ r ‐MMA) with a short perfluoroalkyl chain end. This concept has been applied to PS‐ b ‐P2VP by Zhang et al . using a short PMMA‐containing BCP with a semifluorinated methacrylate block ( Figure ) (non‐preferential interactions between PS and P2VP with PMMA has been demonstrated in previous literature) .…”

“…SEM images of PS‐ b ‐P2VP thin films with 0 wt% (left), 10 wt% (middle), and 20 wt% (right) surface‐active embedded neutral layer. Reproduced with permission . Copyright 2015, American Chemical Society.…”

Perpendicularly aligned nanodomains on versatile substrates via rapid thermal annealing assisted by liquid crystalline ordering in block copolymer films

“…In addition to these three parameters, the interface interactions among the air, BCP and substrate are also substantial factors affecting the nanostructures, especially their orientation within BCP thin lms. [16][17][18][19] Solvent or thermal annealing as a posttreatment is necessary to determine the orientation and alignment of BCP microdomains. [20][21][22][23][24] In industry, thermal annealing is preferred because it avoids the use of solvents and the associated problems, such as dewetting and corrosion.…”

Spatial arrangement of block copolymer nanopatterns using a photoactive homopolymer substrate

“…The resulting self-assembled nanostructures have been applied in a range of areas including in nanolithography, 2 electronic devices 7 and biomaterials. 6,8 In particular, owing to the ability to form sub-20 nm nanopatterns, [9][10][11][12][13][14][15] block copolymer selfassembly has emerged as a viable alternative approach to conventional photolithography with high potential for gaining industrial relevance. Compared to other high resolution lithography techniques such as extreme ultraviolet 16 and electron beam lithography, 17 block copolymer lithography has advantages of potentially high throughput and low cost, and has become one of the most important alternative next-generation lithography techniques.…”