We demonstrate a novel approach for fabricating vertically orientated, sub-10 nm, block copolymer (BCP) nanodomains on a substrate via molecular tailoring of poly(styrene-bmethyl methacrylate) (PS-b-PMMA) BCP, one of the most widely used BCPs for nanopatterning. The idea is to incorporate a short middle block of self-attracting poly(methacrylic acid) (PMAA) between the PS and PMMA blocks, where the PMAA middle block promotes phase separation between PS and PMMA, while maintaining the domain orientation perpendicular to the substrate. The designed PS-b-PMAA-b-PMMA triblock copolymers, which were synthesized via well-controlled anionic polymerization, exhibited order−disorder transition temperatures higher than that of pristine PS-b-PMMA BCPs, indicating the promotion of phase separation by the middle PMAA block. For PS-b-PMAA-b-PMMA BCPs with total molecular weights of 21 and 18 kg/mol, the domain spacing corresponds to 19.3 and 16.7 nm, respectively, allowing us to fabricate sub-10 nm nanodomain structures. More importantly, it was demonstrated that the PMAA middle block, which has a higher surface energy than PS and PMMA, does not significantly alter lateral concentration fluctuations, which are responsible for phase-separation in the lateral direction. This enabled the vertical orientation of microdomains with sub-10 nm feature size on a PS-r-PMMA neutral surface without an additional neutral top layer. We anticipate that this approach provides an important platform for next-generation lithography and nanopatterning applications that require sub-10 nm features over large areas with simple process and reduced cost.
Balancing the interfacial interactions between a polymer and substrate is one of the most commonly employed methods to ensure the vertical orientation of nanodomains in block copolymer lithography. Although a number of technologies have been developed to meet this challenge, there remains a need for a universal solution for surface neutralization that combines simple synthesis, fast processing times, generality toward substrate, low density of film defects, and good surface adhesion. The chemistry of ketenes, which combines highly efficient polymer crosslinking through dimerization and surface adhesion through reaction with the substrate, is shown to be well suited to the challenge. The versatile chemistry of ketenes are accessed through the post‐polymerization of Meldrum's acid, which can be easily incorporated into copolymers through controlled radical polymerization processes. Further, the Meldrum's acid monomer is synthesized on a large scale in one step without the need for chromatography. Processing times of seconds, low defect density, simple synthetic procedures, and good substrate adhesion make these materials attractive as robust block copolymer neutralization layers.
We demonstrated a simple and time-efficient processing method for facilitating a microphase separation of block copolymers (BCPs) based on a single step of spincasting with low volatile solvent and in situ annealing. Wellordered lamellar patterns of poly(styrene-b-methyl methacrylate) BCP films having wide range of molecular weights (51− 235 kg/mol) were fabricated by a single 3 min process of spincasting, even without the conventional pretreatment of substrate neutralization. The formation of this well-ordered lamellar structure is attributed to a synergetic effect between slow solvent evaporation and thermal energy that may provide an efficient cooling profile for the BCP film during the spincasting process. P atterning via self-assembly of block copolymers (BCPs)can be regarded as one of the promising alternatives that overcome the technological and economical limitations associated with photolithographic approaches. 1−6 For instance, with a number of advantages intrinsic to polymer materials, this cost-effective patterning method is expected to replace in part conventional lithographic process for nanoelectronics applications. 7−11 However, despite this potential usability, many technological issues regarding the pattern fidelity and high throughput still remain unresolved, bottlenecking the viability of BCP patterning technology to be used in the actual applications.Low throughput, which is basically due to the slow ordering kinetics of BCPs in molten state, is one of the main obstacles preventing the practical commercialization for BCP patterning. The most common and traditional process for the pattern formation of BCPs relies on the sequential process consisting of substrate neutralization, spin-casting, and thermal annealing (TA), which undesirably takes several hours or days for achieving sufficient phase separation. 12−18 Many works have been done to facilitate the ordering kinetics of BCP thin film, which commonly employs the solvent vapor annealing (SVA) method to infiltrate solvent vapor into the BCP film in the course of phase-separation. 11,19−21 These works have demonstrated that BCPs under SVA become phase-separated more rapidly with enhanced order than under TA, possibly due to lowered local free energy barriers on the ordering pathway as well as the drastic increase in chain mobility in the solventswollen film. In particular, recent SVA approaches suggested that the ordering kinetics is even more facilitated when additional stimuli are combined with SVA. 22−26 Buriak and coworkers demonstrated the ultrafast formation of the BCP pattern using microwaves that instantaneously elevated the solvent vapor pressure and the annealing temperature accelerating ordering kinetics. 25 Ross and co-workers employed a solvothermal annealing setup combining TA and SVA for BCP film accomplishing excellent order within few minutes, 23 which indicates a synergetic effect on facilitating BCP ordering kinetics. While these combined approaches based on SVA is certainly promising for high-throughput BCP patterning in ...
Self-assembly of a binary mixture of poly(styrene)336-block-poly(4-vinyl pyridine)25 (PS336-b-P4VP25) and poly(ethylene glycol)113-block-poly(4-hydroxy styrene)25 (PEG113-b-P4HS25) is shown to give rise to a cylindrical morphology in thin films through pyridine/phenol-based hetero-complementary hydrogen bonding interactions between the P4VP and P4HS copolymer segments. Removal of the cylindrical phase (PEG-b-P4HS) allowed access to porous materials having a pore surface decorated with P4VP polymer blocks. These segments could be transformed into cationic polyelectrolytes through quaternization of the pyridine nitrogen atom. The resulting positively charged nanopore surface could recognize negatively charged gold nanoparticles through electrostatic interactions. This work, therefore, outlines the utility of the supramolecular AB/CD type of block copolymer towards preparation of ordered porous thin films carrying a chemically defined channel surface with a large number of reactive sites.
Block copolymer (BCP) lithography has generally been synonymous to one-or two-dimensional single layered lithographic templates as a means to fabricate simple nanoscaled structures. Recently, the rapidly increasing demand for complex nanostructures and the corresponding evolution in BCP lithography have led to three-dimensional (3D) BCP nanostructures, which can be fabricated in various ways such as directed self-assembly or stacking of cross-linked BCP patterns. This review covers the recent advances in the 3D multilayered structures from cross-linkable BCPs, which provide an easy and robust means for integrating various BCP structures into one scaffold. In this case, wetting-optimized adjustment of BCP microdomains at the layer interface plays a critical role in the formation of well-defined 3D multilayer nanostructures.B lock copolymer (BCP) lithography, referring to a
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