Developing Quantitative Nondestructive Characterization of Nanomaterials: A Case Study on Sequential Infiltration Synthesis of Block Copolymers

The sequential infiltration synthesis (SIS) of inorganic materials in nanostructured block copolymer templates has rapidly progressed in the last few years to develop functional nanomaterials with controllable properties. To assist this rapid evolution, expanding the capabilities of nondestructive methods for quantitative characterization of the materials properties is required. In this paper, we characterize the SIS process on three model polymers with different infiltration profiles through ex situ quantification by reference-free grazing incidence X-ray fluorescence. More qualitative depth distribution results were validated by means of X-ray photoelectron spectroscopy and scanning transmission electron microscopy combined with energy-dispersive X-ray spectroscopy

Block Copolymer Nanolithography for Sub-50 nm Structure Applications

As high technology device patterns are continuing to move towards decreasing critical dimensions and increasing pattern density, there is a need for lithography to move in the same direction. Block copolymer (BCP) lithography is a promising technique, which has single digit nanometer resolution, has a pattern periodicity of about 7-200 nm, and easily scales up to large area at a low cost. The use of BCPs with high immiscibility of constituent blocks, so-called high-Chi material, enables smaller pattern dimensions and is therefore of special interest. However, for lithography techniques to be applicable, also integration into existing nanofabrication processes is necessary. Furthermore, development of techniques to perform sub 10 nm pattern transfer is an enabler for continued device development. This dissertation first provides an overview of the BCP lithography field, to thereafter study the selective infiltration synthesis of alumina into the maltoheptaose block in high-Chi poly(styrene)-block-maltoheptaose of 12 nm pattern periodicity. The infiltration was studied using neutron reflectometry, and a subsequent sub-10 nm pattern transfer was performed into silicon. Also, it studies the process of surface reconstruction of high-Chi poly(styrene)-block-poly(4-vinylpyridine) of 50 nm pattern periodicity, more specifically the effect of time and temperature on pore diameter. Furthermore, pattern transfer of the surface reconstructed BCP film into silicon nitride, and selective area metal-organic vapor phase epitaxy (SA-MOVPE) of indium arsenide vertical nanowires on a silicon platform, using directed self-assembly is demonstrated. By directing the self-assembly along different crystal directions of the substrate, two vertical nanowire configurations were grown. Demonstration of gate all-around stack deposition of oxide/metal to the densely packed nanowire configurations was thereafter made. The results have contributed to the knowledge on BCP lithography and pattern transfer in the sub 50 nm regime, enabling new approaches for applications such as vertical nanowire, or fin transistors

Hyperbolic metamaterials by directed self-assembly of block copolymers

Hyperbolic materials are high uniaxial anisotropic materials that display hyperbolic dispersion with distinctive properties, including negative refraction index, control over light propagation and enhanced Purcell factor. Naturally-occurring hyperbolic materials exhibit these properties only in reduced wavelength ranges, thus limiting their implementation into integrated optical devices. In order to tune the hyperbolic dispersion over broader bandwidths, artificial structures capable to guarantee a greater flexibility, i.e. hyperbolic metamaterials (HMMs), are required. So far, the realization of HMMs that work in the visible and near-infrared wavelength regions has been limited to the out-of-plane configuration due to technological costraints in the fabrication of periodic structures at sub-wavelength dimensions. Here we propose a novel concept of HMMs working in the in-plane configuration, based on the use of block copolymers (BCPs) capable to self-assemble into highly ordered polimeric masks with nanometric feature sizes and periodicity, serving as templates for the subsequent fabrication of hybrid metal-dielectric HMMs. This new class of HMMs can be exploited for metrological applications such as the enhancement of single photon source's (SPS) emission properties

Directed Self-Assembly of High-χ Block Copolymers for Advanced Patterning Applications

High-χ block copolymers (BCP) have gained interest to be used as an alternative to currently used multiple patterning techniques for obtaining sub-lithographic features due to their ability to self-assemble at the nanoscale. However, there is a challenge in controlling the orientation of high-χ BCPs at the air interface. This work describes the use of a formulation-based approach wherein different surface active polymers (SAP) were added as additives to control the orientation of poly(styrene-b-methyl carbonate) (PS-b-PMeCAR) lamellae at the air interface. The resulting thin films made from these formulations showed successful formation of perpendicular lamellae on neutral underlayer substrates upon thermal annealing. The higher surface active SAP demonstrated better orientation control with lower loadings and on thicker films. These films were characterized by atomic force microscopy, grazing incidence small angle x-ray spectroscopy, and x-ray photoelectron spectroscopy to confirm the perpendicular orientation of the lamellar domains and the distribution of the SAP in the BCP thin film. The vertically oriented BCP domains were used as an etch mask by selectively removing the more etch labile PMeCAR block by reactive ion etching using oxygen plasma. A technique called sequential infiltration synthesis (SIS), followed by removing the PS block to obtain ~9.5 nm half pitch domains, was also used. Directed self-assembly via graphoepitaxy was also successfully demonstrated. Future work includes investigation of different BCP platforms and morphologies other than lamellae for patterning work

Hybrid Metrology for Nanostructured Optical Metasurfaces

Metasurfaces have garnered increasing research interest in recent years due to their remarkable advantages, such as efficient miniaturization and novel functionalities compared to traditional optical elements such as lenses and filters. These advantages have facilitated their rapid commercial deployment. Recent advancements in nanofabrication have enabled the reduction of optical metasurface dimensions to the nanometer scale, expanding their capabilities to cover visible wavelengths. However, the pursuit of large-scale manufacturing of metasurfaces with customizable functions presents challenges in controlling the dimensions and composition of the constituent dielectric materials. To address these challenges, the combination of block copolymer (BCP) self-assembly and sequential infiltration synthesis (SIS), offers an alternative for fabrication of high-resolution dielectric nanostructures with tailored composition and optical functionalities. However, the absence of metrological techniques capable of providing precise and reliable characterization of the refractive index of dielectric nanostructures persists. This study introduces a hybrid metrology strategy that integrates complementary synchrotron-based traceable X-ray techniques to achieve comprehensive material characterization for the determination of the refractive index on the nanoscale. To establish correlations between material functionality and their underlying chemical, compositional and dimensional properties, TiO2 nanostructures model systems were fabricated by SIS of BCPs. The results from synchrotron-based analyses were integrated into physical models, serving as a validation scheme for laboratory-scale measurements to determine effective refractive indices of the nanoscale dielectric materials

Nanoscale Self-Assembly: Nanopatterning and Metrology

The self-assembly process underlies a plethora of natural phenomena from the macro to the nano scale. Often, technological development has found great inspiration in the natural world, as evidenced by numerous fabrication techniques based on self-assembly (SA). One striking example is given by epitaxial growths, in which atoms represent the building blocks. In lithography, the use of self-assembling materials is considered an extremely promising patterning option to overcome the size scale limitations imposed by the conventional photolithographic methods. To this purpose, in the last two decades several supramolecular self-assembling materials have been investigated and successfully applied to create patterns at a nanometric scale. Although considerable progress has been made so far in the control of self-assembly processes applied to nanolithography, a number of unresolved problems related to the reproducibility and metrology of the self-assembled features are still open. Addressing these issues is mandatory in order to allow the widespread diffusion of SA materials for applications such as microelectronics, photonics, or biology. In this context, the aim of the present Special Issue is to gather original research papers and comprehensive reviews covering various aspects of the self-assembly processes applied to nanopatterning. Topics include the development of novel SA methods, the realization of nanometric structures and devices, and the improvement of their long-range order. Moreover, metrology issues related to the nanoscale characterization of self-assembled structures are addressed

Strategy for Enhancing Ultrahigh-Molecular-Weight Block Copolymer Chain Mobility to Access Large Period Sizes (>100 nm)

Assembling ultrahigh-molecular-weight (UHMW) block copolymers (BCPs) in rapid time scales is perceived as a grand challenge in polymer science due to slow kinetics. Through surface engineering and identifying a nonvolatile solvent (propylene glycol methyl ether acetate, PGMEA), we showcase the impressive ability of a series of lamellar poly(styrene)-block-poly(2-vinylpyridine) (PS-b-P2VP) BCPs to self-assemble directly after spin-coating. In particular, we show the formation of large-period (≈111 nm) lamellar structures from a neat UHMW PS-b-P2VP BCP. The significant influence of solvent–polymer solubility parameters are explored to enhance the polymer chain mobility. After optimization using solvent vapor annealing, increased feature order of ultralarge-period PS-b-P2VP BCP patterns in 1 h is achieved. Isolated metallic and dielectric features are also demonstrated to exemplify the promise that large BCP periods offer for functional applications. The methods described in this article center on industry-compatible patterning schemes, solvents, and deposition techniques. Thus, our straightforward UHMW BCP strategy potentially paves a viable and practical path forward for large-scale integration in various sectors, e.g., photonic band gaps, polarizers, and membranes that demand ultralarge period sizes