Boundary-directed epitaxy of block copolymers

Si-Containing Reverse-Gradient Block Copolymer for Inorganic Pattern Amplification in EUV Lithography

Although extreme ultraviolet lithography (EUVL) has emerged as a leading technology for achieving high quality sub-10 nm patterns, the insufficient pattern height of photoresist patterns remains a challenge. Directed self-assembly (DSA) of block copolymers (BCPs) is expected to be a complementary technology for EUVL due to its ability to form periodic nanostructures. However, for a combination with EUV patterns, it is essential to develop advanced BCP systems that are suited to inorganic-containing EUV photoresists and offer improved resolution limits, pattern quality, and etch resistance. Here, we report a reverse-gradient BCP system, poly[(styrene-gradient-pentafluorostyrene)-b-4-tert-butyldimetilsiloxystyrene] [P(S-g-PFS)-b-P4BDSS] BCP, which enables universally vertically oriented lamellae even in the absence of a neutral layer, while also containing a Si-containing block with high etch resistance. The gradient block, characterized by a gradual compositional transition from the block junction to the tail, plays a crucial role in creating an adequate surface energy contrast that energetically drives the formation of perpendicular lamellae without neutral layer. When used as a pattern height enhancement layer in EUVL, a high aspect ratio (3.29) of patterns was achieved, thereby offering a supplementary solution for next-generation EUVL.

CO2-Sourced Polymer Dyes for Dual Information Encryption

Large amounts of small molecule dyes leak into the ecosystems annually in harmful and unsustainable ways. Polymer dyes have attracted much attention because of their high migration resistance, excellent stability, and minimized leakage. However, the complex synthesis process, high cost, and poor degradability hinder their widespread application. Herein, green and sustainable polymer dyes are prepared using natural dye quercetin (Qc) and CO2 through a one-step process. The CO2-sourced polymer dyes show strong migration resistance, high stability, and can be degraded on demand. Additionally, the CO2-sourced polymer dyes showed unique responses to Zn2+, leading to significantly enhanced fluorescence, highlighting their potential for information encryption/decryption. The CO2-sourced polymer dyes can solve the environmental hazards caused by small molecule dye leakage and promote the carbon cycle process. Meanwhile, the one-step synthesis process is expected to achieve sustainable and widespread utilization of CO2-sourced polymer dyes.

Aqueous Developable and CO2-Sourced Chemical Amplification Photoresist with High Performance

Seeking high-performance photoresists is an important item for semiconductor industry due to the continuous miniaturization and intelligentization of integrated circuits. Polymer resin containing carbonate group has many desirable properties, such as high transmittance, acid sensitivity and chemical formulation, thus serving as promising photoresist material. In this work, a series of aqueous developable CO2-sourced polycarbonates (CO2-PCs) were produced via alternating copolymerization of CO2 and epoxides bearing acid-cleavable cyclic acetal groups in the presence of tetranuclear organoborane catalyst. The produced CO2-PCs were investigated as chemical amplification resists in deep ultraviolet (DUV) lithography. Under the catalysis of photogenerated acid, the acetal (ketal) groups in CO2-PC were hydrolysed into two equivalents of hydroxyl groups, which change the exposed area from hydrophobicity to hydrophilicity, thus enabling the exposed area to be developed with water. Through normalized remaining thickness analysis, the optimal CO2-derived resist achieved a remarkable sensitivity of 1.9 mJ/cm2, a contrast of 7.9, a favorable resolution (750 nm, half pitch), and a good etch resistance (38 % higher than poly(tert-butyl acrylate)). Such performances outperform commercial KrF and ArF chemical amplification resists (i.e., polyhydroxystyrene-derived and polymethacrylate-based resists), which endows broad application prospects in the field of DUV (KrF and ArF) and extreme ultraviolet (EUV) lithography for nanomanufacturing.

Focused solar annealing for block copolymer fast self-assembly

Block copolymer (BCP) self-assembly has tremendous potential applications in next-generation nanolithography. It offers significant advantages, including high resolution and cost-effectiveness, effectively overcoming the limitations associated with conventional optical lithography. In this work, we demonstrate a focused solar annealing (FSA) technique that is facile, eco-friendly, and energy-efficient for fast self-assembly of polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) thin films. The FSA principle involves utilizing a common biconvex lens to converge incident solar radiation into a high-temperature spot, which is directly used to drive the microphase separation of PS-b-PMMA thin films. As a result, PS-b-PMMA undergoes self-assembly, forming ordered nanostructures in a vertical orientation at seconds timescales on silicon substrates with a neutral layer. In addition, the FSA technique can be employed for grafting neutral polymer brushes onto the silicon substrate. Furthermore, the FSA's compatibility with graphoepitaxy-directed self-assembly (DSA) of BCP is also demonstrated in the patterning of contact holes. The results of contact hole shrinking show that contact hole prepatterns of ∼60.4 nm could be uniformly shrunk to ∼20.5 nm DSA hole patterns with a hole open yield (HOY) of 100 %. For contact hole multiplication, doublet DSA holes were successfully generated on elliptical templates, revealing an average DSA hole size of ∼21.3 nm. Most importantly, due to the direct use of solar energy, the FSA technique provides many significant advantages such as simplicity, environmental friendliness, solvent-free, low cost, and net-zero carbon emissions, and will open up a new direction for BCP lithography that is sustainable, pollution-free, and carbon-neutral.

Coarse-Grained Modeling of EUV Patterning Process Reflecting Photochemical Reactions and Chain Conformations

Enabling extreme ultraviolet lithography (EUVL) as a viable and efficient sub-10 nm patterning tool requires addressing the critical issue of reducing line edge roughness (LER). Stochastic effects from random and local variability in photon distribution and photochemical reactions have been considered the primary cause of LER. However, polymer chain conformation has recently attracted attention as an additional factor influencing LER, necessitating detailed computational studies with explicit chain representation and photon distribution to overcome the existing approach based on continuum models and random variables. We developed a coarse-grained molecular simulation model for an EUV patterning process to investigate the effect of chain conformation variation and stochastic effects via photon shot noise and acid diffusion on the roughness of the pattern. Our molecular simulation demonstrated that final LER is most sensitive to the variation in photon distributions, while material distributions and acid diffusion rate also impact LER; thus, the intrinsic limit of LER is expected even at extremely suppressed stochastic effects. Furthermore, we proposed and tested a novel approach to improve the roughness by controlling the initial polymer chain orientation.

One-pot synthesis of hyperbranched polymers via visible light regulated switchable catalysis

Switchable catalysis promises exceptional efficiency in synthesizing polymers with ever-increasing structural complexity. However, current achievements in such attempts are limited to constructing linear block copolymers. Here we report a visible light regulated switchable catalytic system capable of synthesizing hyperbranched polymers in a one-pot/two-stage procedure with commercial glycidyl acrylate (GA) as a heterofunctional monomer. Using (salen)Co^IIICl (1) as the catalyst, the ring-opening reaction under a carbon monoxide atmosphere occurs with high regioselectivity (>99% at the methylene position), providing an alkoxycarbonyl cobalt acrylate intermediate (2a) during the first stage. Upon exposure to light, the reaction enters the second stage, wherein 2a serves as a polymerizable initiator for organometallic-mediated radical self-condensing vinyl polymerization (OMR-SCVP). Given the organocobalt chain-end functionality of the resulting hyperbranched poly(glycidyl acrylate) (hb-PGA), a further chain extension process gives access to a core-shell copolymer with brush-on-hyperbranched arm architecture. Notably, the post-modification with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) affords a metal-free hb-PGA that simultaneously improves the toughness and glass transition temperature of epoxy thermosets, while maintaining their storage modulus.

Atomically Flat, 2D Edge-Directed Self-Assembly of Block Copolymers

Nanoscale shape engineering is an essential requirement for the practical use of 2D materials, aiming at precisely customizing optimal structures and properties. In this work, sub-10-nm-scale block copolymer (BCP) self-assembled nanopatterns finely aligned along the atomic edge of 2D flakes, including graphene, MoS₂ , and h-BN, are exploited for reliable nanopatterning of 2D materials. The underlying mechanism for the alignment of the self-assembled nanodomains is elucidated based on the wetting layer alternation of the BCP film in the presence of intermediate 2D flakes. The resultant highly aligned nanocylinder templates with remarkably low levels of line edge roughness (LER) and line-width roughness (LWR) yield a sub-10-nm-wide graphene nanoribbon (GNR) array with noticeable switching characteristics (on-to-off ratio up to ≈6 × 10⁴ ).

Sequence-Reversible Construction of Oxygen-Rich Block Copolymers from Epoxide Mixtures by Organoboron Catalysts

Switchable catalysis, in combination with epoxide-involved ring-opening (co)polymerization, is a powerful technique that can be used to synthesize various oxygen-rich block copolymers. Despite intense research in this field, the sequence-controlled polymerization from epoxide congeners has never been realized due to their similar ring-strain which exerts a decisive influence on the reaction process. Recently, quaternary ammonium (or phosphonium)-containing bifunctional organoboron catalysts have been developed by our group, showing high efficiency for various epoxide conversions. Herein, we, for the first time, report an operationally simple pathway to access well-defined polyether-block-polycarbonate copolymers from mixtures of epoxides by switchable catalysis, which was enabled through thermodynamically and kinetically preferential ring-opening of terminal epoxides or internal epoxides under different atmospheres (CO₂ or N₂) using one representative bifunctional organoboron catalyst. This strategy shows a broad substrate scope as it is suitable for various combinations of terminal epoxides and internal epoxides, delivering corresponding well-defined block copolymers. NMR, MALDI-TOF, and gel permeation chromatography analyses confirmed the successful construction of polyether-block-polycarbonate copolymers. Kinetic studies and density functional theory calculations elucidate the reversible selectivity between different epoxides in the presence/absence of CO₂. Moreover, by replacing comonomer CO₂ with cyclic anhydride, the well-defined polyether-block-polyester copolymers can also be synthesized. This work provides a rare example of sequence-controlled polymerization from epoxide mixtures, broadening the arsenal of switchable catalysis that can produce oxygen-rich polymers in a controlled manner.

Confined Growth of DNA-Assembled Superlattice Films

We study the assembly of DNA-functionalized nanocubes under lateral confinement in microscale square trenches on a DNA-functionalized substrate. Microfocus small-angle X-ray scattering (SAXS) and scanning electron microscopy (SEM) are used to characterize the superlattices (SLs). The results indicate that nanocubes form simple-cubic SLs with square-prism morphology and a (100) out-of-plane orientation to maximize DNA bonding. In-plane, SLs align with the template, exposing their {100} side facets, and the degree of alignment depends on trench size. Interestingly, the distribution of in-plane orientations determined from SAXS and SEM do not agree, indicating that the internal and external structures of the SLs differ. To understand this discrepancy, X-ray ptychography is employed to image the internal structures of the SLs, revealing that SLs which appear to be single-crystalline in SEM may have subsurface grain boundaries, depending on trench size. SEM reveals that the SLs grow via nucleation and growth of randomly oriented domains, which then coalesce; this mechanism explains the observed dependence of alignment and defect structure on size. Interestingly, crystallization occurs via an unusual growth mode, whereby continuous SL layers grow on top of several misoriented islands. Overall, this work elucidates the effect of lateral confinement on the crystallization of DNA-functionalized nanoparticles and shows how X-ray ptychography can be used to gain insight into nanoparticle crystallization.

Modular Organoboron Catalysts Enable Transformations with Unprecedented Reactivity

ConspectusElectron-deficient boron-based catalysts with metal-free but metallomimetic characteristics provide a versatile platform for chemical transformations. However, their catalytic performance is usually lower than that of the corresponding metal-based catalysts. Furthermore, many elaborate organoboron compounds are produced via time-consuming multistep syntheses with low yields, presenting a formidable challenge for large-scale applications of these catalysts. Given this context, the development of organoboron catalysts with the combined advantages of high efficiency and easy preparation is of critical importance.Therefore, we envisioned that the construction of a dynamic Lewis multicore system (DLMCS) by integrating the Lewis acidic boron center(s) and a Lewis basic ammonium salt in one molecule would be particularly efficient for on-demand applications because of the intramolecular synergistic effect. This Account summarizes our recent efforts in developing modular organoboron catalysts with unprecedented activities for several chemical transformations. A series of mono-, di-, tri-, and tetranuclear organoboron catalysts was readily designed and prepared in nearly quantitative yields over two steps using commercially available feedstocks. Notably, these catalysts can be modularly tailored by fine control over the electrophilic property of the Lewis acidic boron center(s), electronic and steric effects of the electropositive ammonium cation, linker length between the boron center and the ammonium cation, the number of boron centers, and the nucleophilic anion. This modular design allows systematic manipulation of the reactivity and efficacy of the catalysts, thus optimizing suitable catalysts for versatile chemical transformations. These include the coupling of CO₂ and epoxides, copolymerization of CO₂ and epoxides, ring-opening polymerization (ROP) of epoxides, and ring-opening copolymerization (ROCOP) of epoxides and cyclic anhydrides.The utilization of mononuclear organoboron catalysts provided a turnover frequency of 11050 h^-1 for the CO₂/propylene oxide coupling reaction, an unprecedented efficiency of 5.0 kg of polymer/g of catalyst for the copolymerization of CO₂ and cyclohexene oxide, and a record-breaking catalytic efficiency of 7.4 kg of polymer/g of catalyst for the ROCOP of epoxides with cyclic anhydrides. A turnover number of 56500 was observed at a catalyst loading of 10 ppm for the ROP of epoxides using the dinuclear catalysts. The tetranuclear organoboron catalysts realized the previously intractable task of the copolymerization of CO₂ and epichlorohydrin, producing poly(chloropropylene carbonate) with the highest molecular weight of 36.5 kg/mol reported to date.Furthermore, the study revealed that the interaction between the dynamic Lewis multicore, that is, the intramolecular synergistic effect between the boron center(s) and the quaternary ammonium salt, plays a key role in mediating the catalytic activity and selectivity. This was based on investigations of the crystal structures of the catalysts, key intermediates, reaction kinetics, and density functional theory calculations. The modular tactics for the construction of organoboron catalysts presented in this Account should inspire more advanced catalyst designs.

Self-Aligned Assembly of a Poly(2-vinylpyridine)-b-Polystyrene-b-Poly(2-vinylpyridine) Triblock Copolymer on Graphene Nanoribbons

Directed self-assembly (DSA) of block copolymers is one of the most promising patterning techniques for patterning sub-10 nm features. However, at such small feature sizes, it is becoming increasingly difficult to fabricate the guiding pattern for the DSA process, and it is necessary to explore alternative guiding methods for DSA to achieve long-range ordered alignment. Here, we report the self-aligned assembly of a triblock copolymer, poly(2-vinylpyridine)-b-polystyrene-b-poly(2-vinylpyridine) (P2VP-b-PS-b-P2VP) on neutral graphene nanoribbons with the gap consisting of a P2VP-preferential silicon oxide (SiO₂) substrate via solvent vapor annealing. The assembled P2VP-b-PS-b-P2VP demonstrated long-range, one-dimensional alignment on the graphene substrate in a direction perpendicular to the boundary of the graphene and substrate with a half-pitch size of 8 nm, which greatly alleviates the lithography resolution required for traditional chemoepitaxy DSA. A wide processing window is demonstrated with the gap between graphene stripes varying from 10 to 100 nm, overcoming the restriction on widths of guiding patterns to have commensurate domain spacing. When the gap was reduced to 10 nm, P2VP-b-PS-b-P2VP formed a straight-line pattern on both the graphene and the substrate. Monte Carlo simulations showed that the self-aligned assembly of the triblock copolymer on the graphene nanoribbons is guided at the boundary of parallel and perpendicular lamellae on graphene and SiO₂, respectively. Simulations also indicate that the swelling of a system allows for rapid rearrangement of chains and quickly anneal any misaligned grains and defects. The effect of the interaction strength between SiO₂ and P2VP on the self-assembly is systematically investigated in simulations.

Recent Advances in Sequential Infiltration Synthesis (SIS) of Block Copolymers (BCPs)

In the continuous downscaling of device features, the microelectronics industry is facing the intrinsic limits of conventional lithographic techniques. The development of new synthetic approaches for large-scale nanopatterned materials with enhanced performances is therefore required in the pursuit of the fabrication of next-generation devices. Self-assembled materials as block copolymers (BCPs) provide great control on the definition of nanopatterns, promising to be ideal candidates as templates for the selective incorporation of a variety of inorganic materials when combined with sequential infiltration synthesis (SIS). In this review, we report the latest advances in nanostructured inorganic materials synthesized by infiltration of self-assembled BCPs. We report a comprehensive description of the chemical and physical characterization techniques used for in situ studies of the process mechanism and ex situ measurements of the resulting properties of infiltrated polymers. Finally, emerging optical and electrical properties of such materials are discussed.

Materials Science Challenges to Graphene Nanoribbon Electronics

Graphene nanoribbons (GNRs) have recently emerged as promising candidates for channel materials in future nanoelectronic devices due to their exceptional electronic, thermal, and mechanical properties and chemical inertness. However, the adoption of GNRs in commercial technologies is currently hampered by materials science and integration challenges pertaining to synthesis and devices. In this Review, we present an overview of the current status of challenges, recent breakthroughs toward overcoming these challenges, and possible future directions for the field of GNR electronics. We motivate the need for exploration of scalable synthetic techniques that yield atomically precise, placed, registered, and oriented GNRs on CMOS-compatible substrates and stimulate ideas for contact and dielectric engineering to realize experimental performance close to theoretically predicted metrics. We also briefly discuss unconventional device architectures that could be experimentally investigated to harness the maximum potential of GNRs in future spintronic and quantum information technologies.

Mesoscale Simulations of Polymer Solution Self-Assembly: Selection of Model Parameters within an Implicit Solvent Approximation

Coarse-grained modeling is an outcome of scientific endeavors to address the broad spectrum of time and length scales encountered in polymer systems. However, providing a faithful structural and dynamic characterization/description is challenging for several reasons, particularly in the selection of appropriate model parameters. By using a hybrid particle- and field-based approach with a generalized energy functional expressed in terms of density fields, we explore model parameter spaces over a broad range and map the relation between parameter values with experimentally measurable quantities, such as single-chain scaling exponent, chain density, and interfacial and surface tension. The obtained parameter map allows us to successfully reproduce experimentally observed polymer solution assembly over a wide range of concentrations and solvent qualities. The approach is further applied to simulate structure and shape evolution in emulsified block copolymer droplets where concentration and domain shape change continuously during the process.

Hierarchical Self-Assembly of Thickness-Modulated Block Copolymer Thin Films for Controlling Nanodomain Orientations inside Bare Silicon Trenches

We study the orientation and ordering of nanodomains of a thickness-modulated lamellar block copolymer (BCP) thin film at each thickness region inside a topological nano/micropattern of bare silicon wafers without chemical pretreatments. With precise control of the thickness gradient of a BCP thin film and the width of a bare silicon trench, we successfully demonstrate (i) perfectly oriented lamellar nanodomains, (ii) pseudocylindrical nanopatterns as periodically aligned defects from the lamellar BCP thin film, and (iii) half-cylindrical nanostructure arrays leveraged by a trench sidewall with the strong preferential wetting of the PMMA block of the BCP. Our strategy is simple, efficient, and has an advantage in fabricating diverse nanopatterns simultaneously compared to conventional BCP lithography utilizing chemical pretreatments, such as a polymer brush or a self-assembled monolayer (SAM). The proposed self-assembly nanopatterning process can be used in energy devices and biodevices requiring various nanopatterns on the same device and as next-generation nanofabrication processes with minimized fabrication steps for low-cost manufacturing techniques.