Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session D42: Focus Session: Block Copolymer Thin Films II |
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Sponsoring Units: DPOLY Chair: Chris Ellison, University of Texas at Austin Room: 214B |
Monday, March 2, 2015 2:30PM - 2:42PM |
D42.00001: Minimal Topographic Surfaces for Directed Self-assembly of Cylinder-forming Block Copolymer Thin films with Lateral Order Jaewon Choi, Kenneth Carter, Thomas Russell Controlling the orientation of cylinder-forming block copolymer microdomains in thin films is important for block copolymer applications such as lithographic masks and bit patterned media. However, it is still challenging to produce perfectly ordered cylindrical microdomains with perpendicular orientation over very large areas by using topographical surfaces. Here, we investigate the generation of a single hexagonal array of cylindrical poly(styrene-b-ethylene oxide) (PS-b-PEO) microdomains with perpendicular orientation on minimally patterned surfaces over large areas by thermal annealing without a brush layer. Key factors, such as pattern dimension and film thickness, emerge as being critical for inducing a single grain of perpendicular orientation of PS-b-PEO microdomains over large areas. We systematically investigated the effect of pattern dimension on the generation of perpendicular cylindrical PS-b-PEO microdomains. Furthermore, by solvent vapor annealing, we produced a single grain of parallel cylindrical PS-b-PEO microdomains over large areas on the same minimally patterned surfaces. This simple approach can be an alternative route to achieve the desired orientation of cylinder-forming block copolymer microdomains over large areas. [Preview Abstract] |
Monday, March 2, 2015 2:42PM - 2:54PM |
D42.00002: Pathways toward unidirectional alignment in block copolymer thin films on faceted surfaces Ilja Gunkel, Xiaodan Gu, Abhinav Sarje, Alexander Hexemer, Thomas Russell Solvent vapor annealing (SVA) has been shown recently to be an effective means to produce long-range lateral order in block copolymer (BCP) thin films in relatively short times. Furthermore, using substrates with faceted surfaces allows for generating unidirectionally aligned BCP microdomains on the size scale of an entire wafer. While in recent years SVA has been largely demystified, the detailed pathways toward obtaining unidirectional alignment still remain unclear. Grazing-incidence X-ray scattering (GISAXS) is a very powerful tool for characterizing the structure and morphology of BCPs in thin films, and is particularly useful for studying structural changes in BCP thin films during SVA. We here present in situ GISAXS experiments on cylinder-forming PS-b-P2VP BCP thin films on faceted Sapphire substrates during annealing in THF. We show that the degree of alignment of cylindrical microdomains is greatly enhanced at solvent concentrations close to the order-disorder transition of the copolymer. Furthermore, we observed that inducing disorder by further increasing the solvent concentration and subsequent quenching to the ordered (not yet glassy) state induced the highest degree of alignment with nearly unidirectional alignment of the microdomains in less than 30 min. [Preview Abstract] |
Monday, March 2, 2015 2:54PM - 3:06PM |
D42.00003: Combining Graphoepitaxy and Electric Fields towards Uniaxial Alignment of Solvent-annealed Cylinder forming Poly(styrene)-\textit{block}-poly(dimethylsiloxane) block copolymers Christine Kathrein, Wubin Bai, Larisa Tsarkova, Tao Huang, Apostolos Avgeropoulos, Alexander Boker, Caroline Ross Poly(styrene)-\textit{block}-poly(dimethylsiloxane) (PS-PDMS) is a promising candidate in nanopatterning technologies, since its allows for feature sizes down to 10 nm due to its high chi parameter and good etch selectivity between the blocks. Here we combine the advantages of fast processing of block copolymer films in vapors of selective solvents with orientational guidance of an external electric field and of a graphoepitaxy approach for which we utilize topographic substrates prepared using conventional photolithographic fabrication. Graphoepitaxy was performed between 60 nm high fins composed of SiO$_{\mathrm{2}}$. The degree of ordering strongly depends on the solvent vapor annealing conditions chosen. Highly uniform structures were obtained in a 2:1 volumetric solvent vapor mixture of toluene and heptane at a swelling ratio of 1.8. We demonstrate and analyze the interplay between the dimensions and orientation of topographic features at the substrate, the applied electric field and the composition of the solvent on the degree of ordering in thin films of cylinder-forming PS-PDMS (53 kg/mol, f(PDMS)$=$30{\%}). [Preview Abstract] |
Monday, March 2, 2015 3:06PM - 3:42PM |
D42.00004: Self-Assembly of Diblock Copolymers on Modified and Patterned Surfaces Invited Speaker: Venkat Ganesan The self assembly of diblock copolymer thin films into lamellar and cylindrical structures has been proposed as a method of creating small patterns in polymer thin films for electronic materials applications. A key obstacle, however, is inducing the resulting structures to align perpendicularly, rather than parallel, to the substrate. In this talk, we present our simulation results relating to some strategies which have been pursued by experimentalists to overcome the above goal. One part of this talk will focus on the self-assembly of block copolymers on a homogeneously grafted random copolymer brush composed of the species present in the diblock copolymer. Our study focuses on the ``neutral window'' and examines its dependencies on grafting density, relative chain length between the free and grafted polymers, and blockiness of the random copolymer chains. The second part of this talk will focus on the case of inhomogeneously patterned surfaces and identify the interplay between pattern width and the surface free energies in influencing the alignment in block copolymer films. [Preview Abstract] |
Monday, March 2, 2015 3:42PM - 3:54PM |
D42.00005: Optimizing the Morphology Characterization of Block Copolymer Directed Self-Assembly Thin Films using Inverse Genetic Algorithms Adam Hannon, Daniel Sunday, Donald Windover, Christopher Liman, Juan de Pablo, Joseph Kline Block copolymer (BCP) directed self-assembly (DSA) is one of the leading candidate methods for nanopattern transfer needed in the next generation of integrated circuit and memory storage devices. Much research has gone into precisely controlling the morphology of BCP thin films, making the development and application of metrology methods to BCPs a critical area. In particular, methods for determining the real space structure of the BCP DSA films are needed. Recently, resonant soft X-ray scattering experiments have shown promise as such a method by inversely calculating the real space structure from the scattered intensity profile [Sunday et. al. \textit{ACS Nano} \textbf{2014}, 8 (8), 8426-8437]. These inverse methods are limited in application by their computation speed. Here we present recent work in using genetic algorithms to determine the real space structure of PS-PMMA thin films. The calculated results are compared with the structure found in self-consistent field theory simulations using boundary conditions analogous to the experimental DSA templates. [Preview Abstract] |
Monday, March 2, 2015 3:54PM - 4:06PM |
D42.00006: Instantaneous Formation of Block Copolymer Patterns via Solvo-Thermal Casting Process Hyun Jung Jung, Sanghoon Woo, June Huh, Joona Bang A self-assembly of block copolymers (BCPs) exhibits one of the most promising alternative methods for the next-generation lithography. Many semiconductor companies have explored the possibility of implementing this process in actual chip process, whereas the critical challenges such as feature size control, defect density, and long processing time need to be overcome. Regarding the BCP process, the formation of BCP patterns usually requires long processing time via thermal or solvent annealing. Herein we developed a simple processing method to promote a microphase separation of BCPs using solvo-thermal spin casting process. Spin casting has a very similar mechanism to solvent vapor annealing but its short process time prevents BCP chains from reaching equilibrium morphology. To maximize the chain mobility, we employed a high boiling point solvent and also applied the heat during spin casting. As a result, a well ordered BCP patterns were obtained within less than 5 min via solvo-thermal casting process without further additional annealing step. [Preview Abstract] |
Monday, March 2, 2015 4:06PM - 4:18PM |
D42.00007: Cyclic Solvent Vapor Annealing for Rapid, Robust Vertical Orientation of Features in BCP Thin Films Sean Paradiso, Kris Delaney, Glenn Fredrickson Methods for reliably controlling block copolymer self assembly have seen much attention over the past decade as new applications for nanostructured thin films emerge in the fields of nanopatterning and lithography. While solvent assisted annealing techniques are established as flexible and simple methods for achieving long range order, solvent annealing alone exhibits a very weak thermodynamic driving force for vertically orienting domains with respect to the free surface. To address the desire for oriented features, we have investigated a cyclic solvent vapor annealing (CSVA) approach that combines the mobility benefits of solvent annealing with selective stress experienced by structures oriented parallel to the free surface as the film is repeatedly swollen with solvent and dried. Using dynamical self-consistent field theory (DSCFT) calculations, we establish the conditions under which the method significantly outperforms both static and cyclic thermal annealing and implicate the orientation selection as a consequence of the swelling/deswelling process. Our results suggest that CSVA may prove to be a potent method for the rapid formation of highly ordered, vertically oriented features in block copolymer thin films. [Preview Abstract] |
Monday, March 2, 2015 4:18PM - 4:30PM |
D42.00008: Decoupling Substrate Surface Interactions in Block Polymer Thin Film Self-Assembly Cameron Shelton, Thomas Epps Understanding the impact of the major factors that affect block polymer (BP) thin film self-assembly is necessary to control nanostructure ordering, orientation, and defect density. In this work, we systematically studied the influence of the substrate surface energy, one of the most significant parameters directing self-assembly, on wetting behavior, through-film interactions, and substrate surface field propagation. Notably, we determined the applicability of decoupled surface energy components (dispersive and polar interactions) as opposed to total surface energy, using a suite of chlorosilane monolayers and UV-ozone degradation to create a library of total, dispersive, and polar surface energy effects. Our experimental results combined with surface chemistry literature indicated repulsive total surface energy interactions are the dominant force at the substrate-polymer interface, whereas attractive decoupled surface energy interactions become significant past the contacting layer. This work represents a thorough analysis of a vital force affecting BP self-assembly as well as a blueprint for the generalized design of substrate surfaces that achieve target BP nanostructure orientations for nanolithography, templating, and nanoporous membrane applications. [Preview Abstract] |
Monday, March 2, 2015 4:30PM - 4:42PM |
D42.00009: A Block Copolymer Self-Assembly Approach for 3D Nanoconfined Dopants in Semiconductors Bhooshan Popere, Boris Russ, William Chang, Andrew Heitsch, Peter Trefonas, Rachel Segalman Continuous shrinking of electronic circuits presents a new challenge to demonstrate reliable, uniform nanoscale doping. Directed self-assembly (DSA) of block copolymers (BCP) has proved critical in meeting the technology nodes by enabling excellent pitch control for lithography. Yet, controlling the 3D dopant distribution remains a fundamental design challenge. To this end, we have utilized BCP self-assembly in a novel approach to confine dopants to nanoscopic domains within a semiconductor. The periodic nature of these domains affords precise control over the dosage and spatial positions of dopant atoms. Dopant incorporation within the block copolymer domains via hydrogen bonding eliminates the need for tailored synthesis, making the approach highly modular. Rapid thermal annealing of the self-assembled films effectively drives the dopants into the underlying substrate, thus confining them to within 10-20 nm in all dimensions. Additionally, the size, pitch, dopant dosage and the junction depth can be independently varied for a wide range of dopants. Compositional and electronic measurements indicate that the domains are indeed discrete and nanoconfined. Our approach, thereby, enables a facile method for controlled nanoscopic doping in semiconductors. [Preview Abstract] |
Monday, March 2, 2015 4:42PM - 4:54PM |
D42.00010: Defect motion and annihilation in block copolymer thin films Marcus Mueller, Weihua Li Using self-consistent field theory and computer simulation of a soft, coarse-grained particle model we study defect motion and annihilation in thin films of lamella-forming block copolymers on neutral and chemically patterned substrates. By virtue of the strain-field mediated interactions, dislocation defects with opposite orientation move towards each other. This motion depends both on the thermodynamic, strain-field mediated driving force and the single-chain dynamics that is required to alter the morphology and reduce the distance between the defect cores. This interplay results in a qualitative dependence of the time evolution on the topology of the defect morphology. Upon collision of the defects, they either spontaneously annihilate or form a metastable, tight defect pair. In the latter case, a free-energy barrier has to be overcome to finally produce a defect-free structure. Computing the minimum free-energy path within self-consistent field theory we investigate the dependence of the free-energy barriers of defect motion and annihilation on incompatibility, strength of the chemical surface pattern, and defect morphology. [Preview Abstract] |
Monday, March 2, 2015 4:54PM - 5:06PM |
D42.00011: Accelerating the search for globally stable block polymer microphases using genetic algorithms Carol Tsai, Kris Delaney, Glenn Fredrickson The diverse array of block copolymer (BCP) applications is possible because in the melt state, various morphologies that are periodic structures on the nanoscale emerge depending on the particular composition and architecture of the BCPs used. However, knowing which compositional parameters to use to obtain materials with desired properties is a Herculean task: there is an enormous parameter space to search. Furthermore, the problem is exacerbated by the fact that even at a fixed set of compositional parameters, it is difficult to determine the globally stable morphology and low-lying metastable states that will emerge, as complications arise from a rough free-energy landscape: a self-consistent field search may become trapped in high-energy metastable states, resulting in long and computationally expensive searches. We show that genetic algorithms, which are a biologically-inspired global search heuristic, may be a promising way to ameliorate this problem when used in conjunction with local optimizations performed by SCFT. [Preview Abstract] |
Monday, March 2, 2015 5:06PM - 5:18PM |
D42.00012: Kinetic Aspects of Defect Annihilation in Block Copolymer Thin Films on Patterned Substrates. Su-Mi Hur, Paulina Rincon-Delgadillo, Vikram Thapar, Abelardo Ram\'Irez-Hern\'{a}ndez, Gurdaman Khaira, Paul Nealey, Marcus M\"{u}ller, Juan de Pablo Although there has been significant progress on understanding various aspects of directed self-assembly of block copolymers at equilibrium, important challenges remain regarding the development of materials and processes leading to a perfect, defect-free assembly. We present minimum free-energy pathway calculations for annihilation of dislocation defects in block copolymer thin films using the string method combined with a Theoretically Informed Coarse-Grained (TICG) simulation approach. Our results demonstrate the importance of kinetics in the elimination of defects, where an extraordinarily large thermodynamic driving force is not necessarily sufficient for defect removal. The kinetic path follows fully three-dimensional morphological changes; the corresponding transition states often consist of a very slight connection between an edge dislocation and the neighboring domain. Investigation of the transition states provides useful insights into the possible rate-determining mechanisms for defect motion. We also explore the dependency of the kinetic-energy barriers on the defect type and position, and on processing conditions such as the type of chemical pattern or the strength of the segregation force between the blocks. [Preview Abstract] |
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