Hyo Seon Suh

Sub-10-nm patterning via directed self-assembly of block copolymer films with a vapour-phase deposited topcoat

Directed self-assembly (DSA) of the domain structure in block copolymer (BCP) thin films is a promising approach for sub-10-nm surface patterning. DSA requires the control of interfacial properties on both interfaces of a BCP film to induce the formation of domains that traverse the entire film with a perpendicular orientation. Here we show a methodology to control the interfacial properties of BCP films that uses a polymer topcoat deposited by initiated chemical vapour deposition (iCVD). The iCVD topcoat forms a crosslinked network that grafts to and immobilizes BCP chains to create an interface that is equally attractive to both blocks of the underlying copolymer. The topcoat, in conjunction with a chemically patterned substrate, directs the assembly of the grating structures in BCP films with a half-pitch dimension of 9.3 nm. As the iCVD topcoat can be as thin as 7 nm, it is amenable to pattern transfer without removal. The ease of vapour-phase deposition, applicability to high-resolution BCP systems and integration with pattern-transfer schemes are attractive properties of iCVD topcoats for industrial applications.

Three-Tone Chemical Patterns for Block Copolymer Directed Self-Assembly

Chemical patterns for directed self-assembly (DSA) of lamellae-forming block copolymers (BCP) with density multiplication can be fabricated by patterning resist on a cross-linked polystyrene layer, etching to create guide stripes, and depositing end-grafted brushes in between the stripes as background. To date, two-tone chemical patterns have been targeted with the guide stripes preferentially wet by one block of the copolymer and the background chemistry weakly preferentially wet by the other block. In the course of fabricating chemical patterns in an all-track process using 300 mm wafers, it was discovered that the etching process followed by brush grafting could produce a three-tone pattern. We characterized the three regions of the chemical patterns with a combination of SEM, grazing-incidence small-angle X-ray scattering (GISAXS), and assessment of BCP-wetting behavior, and evaluated the DSA behavior on patterns over a range of guide stripe widths. In its best form, the three-tone pattern consists of guide stripes preferentially wet by one block of the copolymer, each flanked by two additional stripes that wet the other block of the copolymer, with a third chemistry as the background. Three-tone patterns guide three times as many BCP domains as two-tone patterns and thus have the potential to provide a larger driving force for the system to assemble into the desired architecture with fewer defects in shorter time and over a larger process window.

Thermoresponsive switching of liquid flow direction on a two-face prism array

We present a simple approach to reversibly switch the direction of liquid flow on physically symmetric and chemically asymmetric prism structures by exploiting the reversibility of surface wetting properties of a thermo-responsive polymer, poly(N-isopropyl-acrylamide). Such an asymmetric prism array creates a flow path in the direction of the lower critical contact angle. This allows a unidirectional “step flow” across the ridges of prism channels, which can be made reversible with a suitable temperature change.

Characterization of the shape and line-edge roughness of polymer gratings with grazing incidence small-angle X-ray scattering and atomic force microscopy

Grazing-incidence small-angle X-ray scattering (GISAXS) is increasingly used for the metrology of substrate-supported nanoscale features and nanostructured films. In the case of line gratings, where long objects are arranged with a nanoscale periodicity perpendicular to the beam, a series of characteristic spots of high-intensity (grating truncation rods, GTRs) are recorded on a two-dimensional detector. The intensity of the GTRs is modulated by the three-dimensional shape and arrangement of the lines. Previous studies aimed to extract an average cross-sectional profile of the gratings, attributing intensity loss at GTRs to sample imperfections. Such imperfections are just as important as the average shape when employing soft polymer gratings which display significant line-edge roughness. Herein are reported a series of GISAXS measurements of polymer line gratings over a range of incident angles. Both an average shape and fluctuations contributing to the intensity in between the GTRs are extracted. The results are critically compared with atomic force microscopy (AFM) measurements, and it is found that the two methods are in good agreement if appropriate corrections for scattering from the substrate (GISAXS) and contributions from the probe shape (AFM) are accounted for.

Grazing-incidence small angle x-ray scattering studies of nanoscale polymer gratings

Grazing-Incidence Small Angle X-ray Scattering (GISAXS) offers the ability to probe large sample areas, providing three-dimensional structural information at high detail in a thin film geometry. In this study we exploit the application of GISAXS to structures formed at one step of the LiNe (Liu-Nealey) flow using chemical patterns for directed self-assembly of block copolymer films. Experiments conducted at the Argonne National Laboratory provided scattering patterns probing film characteristics at both parallel and normal directions to the surface. We demonstrate the application of new computational methods to construct models based on scattering measured. Such analysis allows for extraction of structural characteristics at unprecedented detail.

Pathways to Mesoporous Resin/Carbon Thin Films with Alternating Gyroid Morphology

Three-dimensional (3D) mesoporous thin films with sub-100 nm periodic lattices are of increasing interest as templates for a number of nanotechnology applications, yet are hard to achieve with conventional top-down fabrication methods. Block copolymer self-assembly derived mesoscale structures provide a toolbox for such 3D template formation. In this work, single (alternating) gyroidal and double gyroidal mesoporous thin-film structures are achieved via solvent vapor annealing assisted co-assembly of poly(isoprene-block-styrene-block-ethylene oxide) (PI-b-PS-b-PEO, ISO) and resorcinol/phenol formaldehyde resols. In particular, the alternating gyroid thin-film morphology is highly desirable for potential template backfilling processes as a result of the large pore volume fraction. In situ grazing-incidence small-angle X-ray scattering during solvent annealing is employed as a tool to elucidate and navigate the pathway complexity of the structure formation processes. The resulting network structures are resistant to high temperatures provided an inert atmosphere. The thin films have tunable hydrophilicity from pyrolysis at different temperatures, while pore sizes can be tailored by varying ISO molar mass. A transfer technique between substrates is demonstrated for alternating gyroidal mesoporous thin films, circumventing the need to re-optimize film formation protocols for different substrates. Increased conductivity after pyrolysis at high temperatures demonstrates that these gyroidal mesoporous resin/carbon thin films have potential as functional 3D templates for a number of nanomaterials applications.

Directed self-oriented self-assembly of block copolymers using chemically modified surfaces

A review of the factors affecting directed self-assembly (DSA) of block copolymers on chemical nanopatterns is presented. The review starts with the formation of chemical patterns suitable for DSA, including patterns and processes that are compatible with industrial fabrication. The critical role of thermodynamics in DSA is then presented, including the impact of chemical pattern geometry and chemistry on the final assembly. The foundation in thermodynamics is also used to explain defect generation and the results observed in DSA with density multiplication. The effect of kinetics in the DSA process is reviewed, focusing on reducing process time to levels that are acceptable for manufacturing process, and the role that kinetics can play in creating trapped defect states. Efforts to achieve sub-10-nm patterning with DSA are shown, including solvent annealing, the use of top-coats, and the synthesis of block copolymers with blocks having similar surface energies. Applications that could benefit from DSA are reviewed, focusing on bit patterned media and fin field-effect transistors. Finally, the integration of DSA on a 300-mm wafer line is presented, including a defect source analysis of DSA on the wafer line.

Mechanistic understanding of tungsten oxide in-plane nanostructure growth via sequential infiltration synthesis

Tungsten oxide (WO3-x) nanostructures with hexagonal in-plane arrangements were fabricated by sequential infiltration synthesis (SIS), using the selective interaction of gas phase precursors with functional groups in one domain of a block copolymer (BCP) self-assembled template. Such structures are highly desirable for various practical applications and as model systems for fundamental studies. The nanostructures were characterized by cross-sectional scanning electron microscopy, grazing-incidence small/wide-angle X-ray scattering (GISAXS/GIWAXS), and X-ray absorption near edge structure (XANES) measurements at each stage during the SIS process and subsequent thermal treatments, to provide a comprehensive picture of their evolution in morphology, crystallography and electronic structure. In particular, we discuss the critical role of SIS Al2O3 seeds toward modifying the chemical affinity and free volume in a polymer for subsequent infiltration of gas phase precursors. The insights into SIS growth obtained from this study are valuable to the design and fabrication of a wide range of targeted nanostructures.

Effect of the Orientation and Bending Stiffness of Nanopatterned Films on Wrinkling

The production of hierarchical structures has an important role for applications such as superhydrophobic surfaces, structural colors, and energy devices. Microscale wrinkling of surfaces decorated by nanoscale patterns can be one of the most efficient methods to realize hierarchical structures. Here, we investigate wrinkling of films embedding anisotropic nanopatterned surfaces prepared by nanoimprint lithography. After transferring nanoimprinted polystyrene thin films onto stretched elastomeric substrates, we achieve microscale wrinkles by releasing the strain. We examine the anisotropic wrinkles of well-defined nanolines with various widths, heights, and spacing ratios and propose a model that considers only bending stiffness of the patterned film. We compare the approach with a model that considers inplane stiffness and confirm that our scheme matches well with that of nanopatterns with thin residual layers.

Ultrathin and Conformal Initiated Chemical-Vapor-Deposited Layers of Systematically Varied Surface Energy for Controlling the Directed Self-Assembly of Block CoPolymers

Directed self-assembly (DSA) of block copolymer (BCP) thin films is a promising approach to enable next-generation patterning at increasingly smaller length scales. DSA utilizes interfacial wetting layers to force the BCP domains to self-assemble with the desired orientation with respect to the substrate. Here, we demonstrate that initiated chemical-vapor-deposited (iCVD) polydivinylbenzene (pDVB) ultrathin films can direct the self-assembly of poly(styrene- block-methylmethacrylate). We found that the methyl radicals formed at increased filament temperatures during the iCVD process result in the backbone methylation of pDVB. By tuning the degree of backbone methylation, we systematically changed the wetting properties of the iCVD pDVB from a slight poly(methylmethacrylate) preference to complete poly(styrene) preference. Additionally, we utilize the conformal nature of the iCVD to form a wetting layer over a topographical line and space pattern, which is subsequently used to produce self-assembled BCP films with both perpendicular orientation and long-range alignment.