Solvent vapor annealing of block copolymers in confined topographies: commensurability considerations for nanolithography

Flash precipitation of random copolymers in a micro-mixer for controlling the size and surface charge of nanoparticles

Precisely controlling the size and surface chemistry of polymeric nanoparticles (P-NPs) is critical for their versatile engineering and biomedical applications. In this work, various NPs of amphipathic random copolymers were comparatively produced by the flash nanoprecipitation (FNP) method using a tube-in-tube type of micro-mixer up to 330 mg min-1 in production scale in a kinetically controlled manner. The NPs obtained from poly(styrene-co-maleic acid), poly(styrene-co-allyl alcohol), and poly(methyl methacrylate-co-methacrylic acid) were concurrently controlled in the range 51-819 nm in size with narrow polydispersity index (<0.1) and -44 to -16 mV in zeta potential, by depending not only on the polymeric chemistry and the concentration but also the mixing behavior of good solvents (THF, alcohols) and anti-solvent (water) under three flow regimes (laminar, vortex and turbulence, turbulent jet). Moreover, the P(St-MA) derived NPs under turbulent jet flow conditions were post-treated in the initial solution mixture for up to 16 h, resulting in lowering of the zeta potential to -52 mV from the initial -27 mV and decreasing size to 46 nm from 50 nm by further migration of hydrophilic segments with -COOH groups on the outer surface, and the removal of THF trapped in the hydrophobic core.

Green Nanofabrication Opportunities in the Semiconductor Industry: A Life Cycle Perspective

The turn of the 21st century heralded in the semiconductor age alongside the Anthropocene epoch, characterised by the ever-increasing human impact on the environment. The ecological consequences of semiconductor chip manufacturing are the most predominant within the electronics industry. This is due to current reliance upon large amounts of solvents, acids and gases that have numerous toxicological impacts. Management and assessment of hazardous chemicals is complicated by trade secrets and continual rapid change in the electronic manufacturing process. Of the many subprocesses involved in chip manufacturing, lithographic processes are of particular concern. Current developments in bottom-up lithography, such as directed self-assembly (DSA) of block copolymers (BCPs), are being considered as a next-generation technology for semiconductor chip production. These nanofabrication techniques present a novel opportunity for improving the sustainability of lithography by reducing the number of processing steps, energy and chemical waste products involved. At present, to the extent of our knowledge, there is no published life cycle assessment (LCA) evaluating the environmental impact of new bottom-up lithography versus conventional lithographic techniques. Quantification of this impact is central to verifying whether these new nanofabrication routes can replace conventional deposition techniques in industry as a more environmentally friendly option.

Directed Self-Assembly of Block Copolymers for the Fabrication of Functional Devices

Directed self-assembly of block copolymers is a bottom-up approach to nanofabrication that has attracted high interest in recent years due to its inherent simplicity, high throughput, low cost and potential for sub-10 nm resolution. In this paper, we review the main principles of directed self-assembly of block copolymers and give a brief overview of some of the most extended applications. We present a novel fabrication route based on the introduction of directed self-assembly of block copolymers as a patterning option for the fabrication of nanoelectromechanical systems. As a proof of concept, we demonstrate the fabrication of suspended silicon membranes clamped by dense arrays of single-crystal silicon nanowires of sub-10 nm diameter. Resulting devices can be further developed for building up high-sensitive mass sensors based on nanomechanical resonators.

Temperature-Controlled Solvent Vapor Annealing of Thin Block Copolymer Films

Solvent vapor annealing is as an effective and versatile alternative to thermal annealing to equilibrate and control the assembly of polymer chains in thin films. Here, we present scientific and practical aspects of the solvent vapor annealing method, including the discussion of such factors as non-equilibrium conformational states and chain dynamics in thin films in the presence of solvent. Homopolymer and block copolymer films have been used in model studies to evaluate the robustness and the reproducibility of the solvent vapor processing, as well as to assess polymer-solvent interactions under confinement. Advantages of utilizing a well-controlled solvent vapor environment, including practically interesting regimes of weakly saturated vapor leading to poorly swollen states, are discussed. Special focus is given to dual temperature control over the set-up instrumentation and to the potential of solvo-thermal annealing. The evaluated insights into annealing dynamics derived from the studies on block copolymer films can be applied to improve the processing of thin films of crystalline and conjugated polymers as well as polymer composite in confined geometries.

Three-dimensional electroactive ZnO nanomesh directly derived from hierarchically self-assembled block copolymer thin films

Three-dimensional (3D) nanoarchitectures can offer enhanced material properties, such as large surface areas that amplify the structures' interaction with environments making them useful for various sensing applications. Self-assembled block copolymers (BCPs) can readily generate various 3D nanomorphologies, but their conversion to useful inorganic materials remains one of the critical challenges against the practical application of self-assembled BCPs. This work reports the vapor-phase infiltration synthesis of optoelectrically active, 3D ZnO nanomesh architectures by combining hierarchical successive stacking of self-assembled, lamellar-phase polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) BCP thin films and a modified block-selective vapor-phase material infiltration protocol. The 3D ZnO nanomesh exhibits optoelectrical functionality, featuring stack-layer-number-dependent electrical conductance resembling the percolative transport originating from the intrinsic morphological network connectivity of the lamellar BCP pattern with symmetric block ratio. The results not only illustrate the first demonstration of electrical functionality based on the ZnO nanoarchitecture directly generated by the infiltration synthesis in self-assembled BCP thin films but also present a new, large-area scalable, metal oxide thin film nanoarchitecture fabrication method utilizing industry-compatible polymer solution coating and atomic layer deposition. Given the large surface area, three-dimensional porosity, and readily scalable fabrication procedures, the generated ZnO nanomesh promises potential applications as an efficient active medium in chemical and optical sensors.

Fabrication of Si and Ge nanoarrays through graphoepitaxial directed hardmask block copolymer self-assembly

Films of self assembled diblock copolymers (BCPs) have attracted significant attention for generating semiconductor nanoarrays of sizes below 100 nm through a simple low cost approach for device fabrication. A challenging abstract is controlling microdomain orientation and ordering dictated by complex interplay of surface energies, polymer-solvent interactions and domain spacing. In context, microphase separated poly (styrene-b-ethylene oxide) (PS-b-PEO) thin films is illustrated to fabricate nanopatterns on silicon and germanium materials trenches. The trenched templates was produced by simple electron beam lithography using hydrogen silsesquioxane (HSQ) resist. The orientation of PEO, minority cylinder forming block, was controlled by controlling trench width and varying solvent annealing parameters viz. temperature, time etc. A noticeable difference in microdomain orientation was observed for Si and Ge trenches processed under same conditions. The Ge trenches promoted horizontal orientations compared to Si due to difference in surface properties without any prior surface treatments. This methodology allows to create Ge nanopatterns for device fabrication since native oxides on Ge often induce patterning challenges. Subsequently, a selective metal inclusion method was used to form hardmask nanoarrays to pattern transfer into those substrates through dry etching. The hardmask allows to create good fidelity, low line edge roughness (LER) materials nanopatterns.

Carbohydrate-based block copolymer systems: directed self-assembly for nanolithography applications

Self-assembly of block copolymers (BCPs) provides an attractive nanolithography approach, which looks especially promising for fabrication of regular structures with characteristic sizes below 10 nm. Nevertheless, directed self-assembly (DSA) and pattern transfer for BCPs with such small features remain to be a challenge. Here we demonstrate DSA of the maltoheptaose-block-polystyrene (MH_1,2k-b-PS_4,5k) BCP system using graphoepitaxy. BCP thin films were self-organized by solvent vapor annealing in tetrahydrofuran (THF) and water into sub-10 nm scale cylinders of the maltoheptaose (MH) block oriented horizontally or perpendicularly to the surface in a polystyrene (PS) matrix. The guiding patterns for graphoepitaxy were made by the electron beam lithography (EBL) and lift-off process with the distance gradually varying between 0 and 200 nm. Atomic force microscopy (AFM) investigation of MH_1,2k-b-PS_4,5k BCP DSA patterns revealed good ordering of vertical and horizontal cylindrical MH arrays for DSA lines with 150-200 nm separation. Reactive ion etching (RIE) of MH_1,2k and PS_4,5k thin films in O₂ and CF₄ plasma showed up to 14 times higher etch rate of MH compared to PS. These results indicate that MH_1,2k-b-PS_4,5k is a promising BCP for nanolithographic applications below 10 nm.

Creating Active Device Materials for Nanoelectronics Using Block Copolymer Lithography

The prolonged and aggressive nature of scaling to augment the performance of silicon integrated circuits (ICs) and the technical challenges and costs associated with this has led to the study of alternative materials that can use processing schemes analogous to semiconductor manufacturing. We examine the status of recent efforts to develop active device elements using nontraditional lithography in this article, with a specific focus on block copolymer (BCP) feature patterning. An elegant route is demonstrated using directed self-assembly (DSA) of BCPs for the fabrication of aligned tungsten trioxide (WO₃) nanowires towards nanoelectronic device application. The strategy described avoids conventional lithography practices such as optical patterning as well as repeated etching and deposition protocols and opens up a new approach for device development. Nanoimprint lithography (NIL) silsesquioxane (SSQ)-based trenches were utilized in order to align a cylinder forming poly(styrene)-block-poly(4-vinylpyridine) (PS-b-P4VP) BCP soft template. We outline WO₃ nanowire fabrication using a spin-on process and the symmetric current-voltage characteristics of the resulting Ti/Au (5 nm/45 nm) contacted WO₃ nanowires. The results highlight the simplicity of a solution-based approach that allows creating active device elements and controlling the chemistry of specific self-assembling building blocks. The process enables one to dictate nanoscale chemistry with an unprecedented level of sophistication, forging the way for next-generation nanoelectronic devices. We lastly outline views and future research studies towards improving the current platform to achieve the desired device performance.

Strategies for Inorganic Incorporation using Neat Block Copolymer Thin Films for Etch Mask Function and Nanotechnological Application

Block copolymers (BCPs) and their directed self-assembly (DSA) has emerged as a realizable complementary tool to aid optical patterning of device elements for future integrated circuit advancements. Methods to enhance BCP etch contrast for DSA application and further potential applications of inorganic nanomaterial features (e.g., semiconductor, dielectric, metal and metal oxide) are examined. Strategies to modify, infiltrate and controllably deposit inorganic materials by utilizing neat self-assembled BCP thin films open a rich design space to fabricate functional features in the nanoscale regime. An understanding and overview on innovative ways for the selective inclusion/infiltration or deposition of inorganic moieties in microphase separated BCP nanopatterns is provided. Early initial inclusion methods in the field and exciting contemporary reports to further augment etch contrast in BCPs for pattern transfer application are described. Specifically, the use of evaporation and sputtering methods, atomic layer deposition, sequential infiltration synthesis, metal-salt inclusion and aqueous metal reduction methodologies forming isolated nanofeatures are highlighted in di-BCP systems. Functionalities and newly reported uses for electronic and non-electronic technologies based on the inherent properties of incorporated inorganic nanostructures using di-BCP templates are highlighted. We outline the potential for extension of incorporation methods to triblock copolymer features for more diverse applications. Challenges and emerging areas of interest for inorganic infiltration of BCPs are also discussed.

Morphological evolution of lamellar forming polystyrene-block-poly(4-vinylpyridine) copolymers under solvent annealing

In this work, we are reporting a very simple and efficient method to form lamellar structures of symmetric polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) copolymer thin films with vertically (to the surface plane) orientated lamellae using a solvent annealing approach. The methodology does not require any brush chemistry to engineer a neutral surface and it is the block neutral nature of the film-solvent vapour interface that defines the orientation of the lamellae. The microphase separated structure of two different molecular weight lamellar forming PS-block-P4VP copolymers formed under solvent vapour annealing was monitored using atomic force microscopy (AFM) so as to understand the morphological changes of the films upon different solvent exposure. In particular, the morphology changes from micellar structures to well-defined microphase separated arrangements. The choice of solvent/s (single and dual solvent exposure) and the solvent annealing conditions (temperature, time etc.) has important effects on structural transitions of the films and it was found that a block neutral solvent was required to realize vertically aligned P4VP lamellae. The results of the structural variation of the phase separated nanostructured films through the exposure to ethanol are also described.