Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session T19: Focus Session: Thin Films of Block Copolymers and Hybrid Materials II - Directed Self Assembly |
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Sponsoring Units: DPOLY Chair: Chaitanya Ullal, Department of Materials Science and Engineering, Rensselaer Polytechnic Institute Room: 404 |
Thursday, March 6, 2014 11:15AM - 11:27AM |
T19.00001: Impact of stereocomplexation on the directed self-assembly poly (styrene-$b$-\textit{(rac)}-lactide) on chemically patterned surfaces Xiao Li, Yadong Liu, Abelardo Ramirez-Hernandez, Juan J. de Pablo, Shengxiang Ji, Paul Nealey Poly (styrene) - block -- poly (\textit{rac}- lactide) (PS-\textit{b(rac)}PLA) with bulk lamellar period, L$_{\mathrm{o}}$, was directed to assemble on chemically patterned surfaces with period , L$_{\mathrm{s}}$. The surface energies of the blocks are similar enabling thermal annealing of the films. The racemic PLA block including short sequences of L- and D-lactide acid chains formed stereocomplexes. PS-\textit{b(rac)}PLA could be directed to assemble with a high degree of perfection over the entire range of 1 \textless L$_{\mathrm{s}}$/L$_{\mathrm{o}}$ \textless 2. As the L$_{\mathrm{o}}$ increased to accommodate the larger L$_{\mathrm{s}}$, the width of the PS domain increased faster than PLA domain. This behavior contrasts sharply with the lamellae-forming systems without strong inter-chain interactions for which assembly occurs for 1\textless L$_{\mathrm{s}}$/L$_{\mathrm{o}}$ \textless 1.1. Experimental and molecular simulation results will be discussed in the context of non-equilibrium assembly behavior of triblock copolymers, and the potential for chemical complexity and chain architecture to improve the function block polymer materials for lithographic applications. [Preview Abstract] |
Thursday, March 6, 2014 11:27AM - 11:39AM |
T19.00002: Directed Assembly of Lamellae Forming Block Copolymer Thin Films near the Order-Disorder Transition Sangwon Kim, Paul Nealey, Frank Bates The impact of thin film confinement on the ordering of a lamellar morphology was investigated using partially epoxidized poly(styrene-$b$-isoprene) diblock copolymers bound by non-preferential wetting interfaces. Even in the 2-dimensional limit (\textless L\textgreater $\to $ L$_{0}$, where \textless L\textgreater and L$_{0}$ denote the average film thickness and the periodicity, respectively), the composition fluctuations are observed at the crossover from the ordered to the disordered states, establishing the order-disorder transition temperature (T$_{ODT})$ in thin films. While the minimum feature size of block copolymers achievable for nanolithography is set effectively by the T$_{ODT}$, the dimensionality reduction leaves the T$_{ODT}$ unaffected compared to the bulk limit within experimental error. Directed self-assembly with the half pitch (L$_{0}$/2) \textless 8 nm has been accomplished using chemical patterning near T$_{ODT}$. [Preview Abstract] |
Thursday, March 6, 2014 11:39AM - 11:51AM |
T19.00003: Directed self-assembly (DSA)of block copolymer-based supramolecular materials on chemically patterned surfaces Guangpeng Wu, Paul Nealey Supramolecular systems composed of coil-coil block copolymers in which small molecules are attached to the segments of one of the blocks through hydrogen-bonding interactions are of interest because they form well-defined hierarchical three-dimensional nanostructures, and the small molecules can be designed to impart functionality to the system. Previous studies have investigated the self-assembled structure-property relationships of these coil-comb molecules in the bulk and in thin films. Here we investigate the potential for directing the assembly of this class of materials on chemically nanopatterned surfaces. A lamellae-forming supramolecular system was created by attaching 3-pentadecylphenol (PDP) to the vinylpyridine segments of polystyrene-\textit{block}-poly(4-vinylpyridine) (PS-$b$-P4VP) via hydrogen bonding. The period of the lamellar structure could be controlled between 35 nm to 40 nm by changing the volume fraction of PDP. The materials were solvent annealed on chemical patterns consisting of stripes of PS on silicon substrates. Analogous to the DSA of coil-coil block copolymers, the quality of the arrays of perpendicularly oriented through-film domains depended on the period of the chemical patterns, the PDP/4VP fraction, the width of the PS stripes, and the film thickness. [Preview Abstract] |
Thursday, March 6, 2014 11:51AM - 12:03PM |
T19.00004: Dynamics of Defect Annihilation in Directed Self-Assembly of Block Copolymers Using Optical Inspection of Fully Patterned Wafers Paulina Rincon Delgadillo, Roel Gronheid, Paul Nealey Research in directed self-assembly (DSA) of block copolymers (BCP) has gained significant interest from the industry due to its potential application as a complimentary lithographic technique. This has led to the implementation of different DSA schemes, the Liu-Nealey (LiNe) chemo-epitaxy flow among others, in a fab environment, with automatic processing and specialized materials. This set-up allows a thorough evaluation of the impact of the boundary conditions on the assembly process that cannot be performed in the laboratory. In addition, the inspection tools allow the characterization of large areas of nano-patterns and provide enough information to perform statistical analysis of the assembly process. Using optical inspection, a high capture rate of dislocation defects has been achieved and fine differences in the chemically nano-patterned substrates have been related to the final defect density. At the same time, multiple time and temperature conditions during BCP anneal have been investigated. With this work, we identified the role of the boundaries (thermodynamics) and kinetics on defect annihilation on DSA of BCP using density multiplication. [Preview Abstract] |
Thursday, March 6, 2014 12:03PM - 12:15PM |
T19.00005: Finding Optimal Templates for the Directed Self-Assembly of Thin Film Block Copolymers with Inverse Self-Consistent Field Theory Simulations Adam Hannon, Yi Ding, Wubin Bai, Caroline Ross, Alfredo Alexander-Katz Achieving sub-10 nm patterns with non-periodic features is a key goal in the development of next generation integrated circuits devices. One route to create such features at this length scale is the directed self-assembly of thin film block copolymers (BCPs). Inverse design methods are becoming a key part in developing templates needed for given target patterns where the required template is both non-intuitive and requires optimization. Here we use a self-consistent field theory based inverse design algorithm to find template solutions for target structures. Recent studies have revealed a wide parameter space with multiple solutions for given target structures. Using fidelity and topology functions, we characterize how well different template solutions yield given target structures and refine these solutions beyond simply being free energy minimum solutions. Experiments using polystyrene-$b$-polydimethylsiloxane BCPs templated by hydrogen silsesquioxane posts are used for verifying and refining the simulation results. Results show that key factors influencing the fidelity and topology of the samples include the effective volume fraction of the solvent annealed system, size of the posts, and areal post density. Optimization of these parameters achieves refined template solutions with better reproducibility and lower defectivity both computationally and experimentally. [Preview Abstract] |
Thursday, March 6, 2014 12:15PM - 12:27PM |
T19.00006: Directed self-assembly of ABA triblock copolymer on chemical contrast pattern for sub-10nm nanofabrication by solvent annealing Shisheng Xiong, Lei Wan, Yves-Andre Chapuis, Thomas Albrecht, Ricardo Ruiz, Paul F. Nealey We report a room temperature solvent annealing method for directed self-assembly of symmetric ABA triblock copolymer to form perpendicularly oriented lamellae on chemical patterns.~~The phase separation of ABA triblock copolymer is analogous to the counterpart AB diblock copolymer with half molecular weight. However, a much broader neutral window for surface wetting was found for the triblock. After exposing to the solvent vapor for a certain time, thin films of a symmetric poly (2-vinylpyridine-styrene-$b$-2-vinylpyridine) (P2VP-b-PS-$b$-P2VP) triblock copolymer self assemble, while the nanostructure is retained after rapid solvent evaporation. The perpendicular lamellae with sub-10nm feature size can be assembled with density multiplication on lithographically defined chemical pre-patterns to form registered periodic arrays of striped patterns with exacting precision in continuously varying period and spacing. Using block-selective infiltration (Atomic layer deposition with sequential long soaking/purge cycles), the alumina composite with high etch resistance was specifically incorporated into the polar and hydrophilic P2VP domains. The sub-10nm scale surface pattern was stransferred into Si substrates by plasma etching. [Preview Abstract] |
Thursday, March 6, 2014 12:27PM - 1:03PM |
T19.00007: Measurement of the Buried Structure of Sub-30 nm Block Copolymer Lithography Patterns Using Resonant X-ray Scattering Invited Speaker: Joseph Kline The semiconductor industry is pushing the limits of conventional optical lithography. According to the ITRS roadmap, new lithographic methods will be required to economically produce the smaller patterned features of future processing generations. Technologies being evaluated to produce these finer feature sizes include extreme ultraviolet lithography, multiple-beam electron beam lithography, multiple exposures, and directed self-assembly (DSA) of block copolymers (BCPs). One of the critical questions remaining for BCP lithography is the buried structure and potential 3D defects not visible with surface characterization methods such as scanning electron microscopy and atomic force microscopy. We have combined resonant soft x-ray scattering with critical-dimension small-angle x-ray scattering (CD-SAXS) to determine the buried structure of the two blocks, the interfacial roughness, and the pitch uniformity in native BCP films with sub-12 nm features with programmed changes in the template. We found samples that had similar top surface structure often had substantial variations in their buried structure. We also found that lamella on a neutral surface were almost always different from the neighboring lamella on a preferential surface. We will discuss how these insights into the 3D structure of the block copolymer interface correspond to computational simulations of the directed self-assembly process of line-space pattern gratings. [Preview Abstract] |
Thursday, March 6, 2014 1:03PM - 1:15PM |
T19.00008: Directed self-assembly of lamellae-forming block copolymer with density multiplication for high aspect ratio structures Xuanxuan Chen, Paulina Rincon Delgadillo, Zhang Jiang, Jin Wang, Joseph Strzalka, Paul Nealey Directed self-assembly (DSA) of block copolymers provides the means to control structure over micro- and macroscopic dimensions. We investigate the potential for DSA to control nanostructure through sub-micron film thickness and realize near perfect structure in the plane of the film over macroscopic areas. Lamellae-forming poly (styrene) - block - poly (methyl methacrylate) (L$_{\mathrm{0}}=$28.5nm) was directed to assemble on chemical patterns with a pitch (L$_{\mathrm{S}})_{\mathrm{\thinspace }}$of 84nm. The three-dimensional structure of the films was characterized by SEM and GISAXS as a function of the geometry and chemistry of the chemical pattern, film thickness, and thermal annealing time. At optimal conditions, perpendicular through film structures was achieved with aspect ratio of 12 over 5 x 8 mm$^{\mathrm{2}}$ areas in 3 hours at 250 C. At non-optimal boundary conditions, time for assembly increases, and the maximum film thickness decreases, suggesting an assembly mechanism involving nucleation of structure at the pattern and free surface and differing governance of the pattern-directed structure in both the thermodynamics and kinetics of the system. GISAXS experiments reveals that a significant number of defect structures persist within the films even after the surface structures are perfectly aligned. [Preview Abstract] |
Thursday, March 6, 2014 1:15PM - 1:27PM |
T19.00009: Wetting Transition and Directed Assembly of Block Copolymers on UVO Tunable Nanopatterned Elastomeric Substrates Arzu Hayirlioglu, Manish Kulkarni, Alamgir Karim Controlled self-assembly of block copolymers (BCP) on flexible substrates will enable use of these unique structures in various future applications such as photovoltaic devices, capacitors, and high-density data storage devices. A notable challenge in this regard is that successful deployment of BCPs requires an understanding of BCP ordering properties on flexible substrate as a function of the surface chemistry, topography including patterning, roughness, stiffness, etc. In our studies, the surface energy (SE) of PDMS substrates was varied by UV-ozone exposure of the smooth elastomeric substrates and results indicated that a dewetting to wetting transition occurred with increasing PDMS surface energy. Consequently, the morphology variations in the wetting regime was fully investigated for cylinder and lamellae forming BCP films. Recently, we discovered that creating a uniform nanopatterned surface on PDMS substrates yields induced stability to BCP films. This allows to utilize the full range SE regime (20-70 mJ/m$^{2})$ to create stable BCP films and to examine the desired morphological behavior of BCP films on flexible substrates. This significant result allows us to exploit to full range of SE of flexible substrates for next generation of functional BCP films in flexible devices. [Preview Abstract] |
Thursday, March 6, 2014 1:27PM - 1:39PM |
T19.00010: Fabrication of large-area arrays of hybrid nanostructures on polymer-derived chemically patterned surfaces Xiaoying Liu, Dhriti Nepal, Sushmita Biswas, Kyoungweon Park, Richard Vaia, Paul Nealey The precise placement and assembly of nanoparticles (NPs) into large-area nanostructure arrays will allow for the design and implementation of advanced nanoscale devices for applications in fields such as quantum computing, optical sensing, superlenses, photocatalysis, photovoltaics, and non-linear optics. Our work is focused on using chemically nanopatterned surfaces to fabricate arrays of hybrid nanostructures with each component of the building block at well-defined positions. The precise chemical contrast patterns with densities and resolution of features created using standard tools of lithography, polymer self-assembly, and surface functionalization allow for control of position and interparticle spacing through selective surface-particle and particle-particle interactions. We have demonstrated the assembly of NPs, including metallic NPs and semiconductor quantum dots, into arrays of hybrid structures with various geometries, such as monomers, dimers, quatrefoils, stripes, and chains. We have developed protocols to fabricate NP arrays over a variety of substrates, which allows for the design and characterization of optical and electronic nanostructures and devices to meet the requirements of various technological applications. [Preview Abstract] |
Thursday, March 6, 2014 1:39PM - 1:51PM |
T19.00011: Templated Co-assembly of PS-b-PDMS Block Copolymer and Inorganic Nanoparticles Yi Ding, Kevin Gotrik, Ou Chen, Moungi Bawendi, Caroline Ross, Alfredo Alexander-Katz We studied the co-assembly behavior of block copolymer (BCP) and inorganic nanoparticles (NPs) with post arrays as graphoepitaxial template. We have developed a fabrication/characterization procedure for thin films composed of oil-soluble NPs (e.g. quantum dots capped with oleic acid and oleylamine) and polystyrene-\textit{b}-polydimethylsiloxane (PS-\textit{b}-PDMS) BCP. According to our experiments, NPs demonstrated a tendency to gather at defect points (X-shape, T-shape, L-shape) of the cylinder forming PDMS domain. Based upon this property, we used chemically functionalized hydrogen silsesquioxane (HSQ) posts as templates to direct the BCP-NPs co-assembly. The HSQ posts were designed in such a way that the cylinder-phase of PS-\textit{b}-PDMS BCP can form X-shape and T-shape structure. Different conditions to control the location of the NPs within the thin film were studied. [Preview Abstract] |
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