Browsing by Subject "Block copolymers"
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Item Advanced materials for block copolymer lithography(2013-05) Bates, Christopher Martin; Willson, C. Grant, 1939-The multi-billion dollar per year lithography industry relies on the fusion of chemistry, materials science, and engineering to produce technological innovations that enable continual improvements in the speed and storage density of microelectronic devices. A critical prerequisite to improving the computers of today relies on the ability to economically and controllably form thin film structures with dimensions on the order of tens of nanometers. One class of materials that potentially meets these requirements is block copolymers since they can self-assemble into structures with characteristic dimensions circa three to hundreds of nanometers. The different aspects of the block copolymer lithographic process are the subject of this dissertation. A variety of interrelated material requirements virtually necessitate the synthesis of block copolymers specifically designed for lithographic applications. Key properties for the ideal block copolymer include etch resistance to facilitate thin film processing, a large interaction parameter to enable the formation of high resolution structures, and thin film orientation control. The unifying theme for the materials synthesized herein is the presence of silicon in one block, which imparts oxygen etch resistance to just that domain. A collection of silicon-containing block copolymers was synthesized and characterized, many of which readily form features on approximately the length scale required for next-generation microelectronic devices. The most important thin film processing step biases the orientation of block copolymer domains perpendicular to the substrate by control of interfacial interactions. Both solvent and thermal annealing techniques were extensively studied to achieve orientation control. Ultimately, a dual top and bottom surface functionalization strategy was developed that utilizes a new class of "top coats" and cross-linkable substrate surface treatments. Perpendicular block copolymer features can now be produced quickly with a process amenable to existing manufacturing technology, which was previously impossible. The development of etching recipes and pattern transfer processes confirmed the through-film nature of the features and the efficacy of both the block copolymer design and the top coat process.Item Advanced organic materials for lithographic applications(2010-08) Strahan, Jeffrey Ryan; Willson, C. G. (C. Grant), 1939-; Anslyn, Eric V.; Freeman, Benny D.; Iverson, Brent L.; Willets, Katherine A.The microelectronics industry is driven by the need to produce smaller transistors at lower costs, and this requires an ever-changing approach to the chemistry involved in their fabrication. While photolithography has been able to keep pace with Moore’s law over the past four decades, alternative patterning technologies are now receiving increased attention to keep up with market demand. The first project describes work towards increasing the sensitivity of electron-beam resists by incorporating electron-withdrawing groups into the alpha position of methacrylates. After monomer design and synthesis, several polymers were synthesized that investigated the role of fluorine in the resists performance. G-values, electron-beam contrast curves, and EUV imaging showed that these fluorinated polymethacrylates outperformed current industrial resists. The next project deals with the design, synthesis, and evaluation of a resist that seeks to decouple chemical amplification from acid diffusion. While work was shown that a system comprised of a photo-labile polyphthalaldehyde and x novolak could achieve this process, the high dose required to image was problematic. An aliphatic dialdehyde was envisioned to account for these issues, but its synthesis was never achieved. A polyethylene glycol aldehyde was synthesized and polymerized, but its material properties did not perform the intended function. Ultimately, the stability of aliphatic aldehydes proved to be too unstable for this project to continue. While the synthesis was troublesome, a fundamental study of ceiling temperatures was undertaken. Numerical and analytical solutions were developed that describe the exact nature of the equilibrium constant on a living polymer system. These results were verified by a VT-NMR experiment, which accurately predicted the ceiling temperature of polythalaldehyde with a Van’t Hoff plot. Lastly, the self-assembly of block copolymers was investigated as a means to produce high resolution, high density nano-imprint lithography templates for bit patterned media. The first set of experiments involved synthesizing polymeric cross-linked surface treatments from substituted styrenes. The aryl substituent was shown to largely effect the surface energy, and after anionically synthesizing PS-b-PMMA, these materials were shown to effect block copolymer orientation. To produce a 3-D pattern of the self-assembled features, silicon was incorporated into one block to provide adequate etch resistance. Several monomers were investigated, and two, an isoprene and methacrylate analog, were successfully incorporated into two block copolymers. The silicon containing methacrylate derivative polymer was shown to successfully self-assemble in thin films under solvent annealing conditions.Item Block copolymer thin films : interfacial and confinement effects(2002-05) Limary, Ratchana; Green, Peter F. (Peter Fitzroy)Item Design of silicon-containing block copolymer materials for applications in lithography(2016-12) Blachut, Gregory; Willson, C. Grant, 1939-; Ellison, Christopher J.; Ganesan, Venkat; Mack, Chris A.; Akinwande, DejiContinual advancement in microelectronic performance has made microelectronics essentially ubiquitous, enriching modern life in ways unimaginable even a few decades ago. The advancement in microelectronic devices is made possible by advancements in the manufacturing processes used to make them. Chief among these technologies is lithography, the process by which the individual components on the device are patterned. At present, complex and complicated double-patterning processes are being used to extend the resolution of the lithographic methods used in high-volume manufacturing, but only at great cost. Future generations of microelectronic devices will require even further use of multiple-patterning processes, at which point the economics of manufacturing could prevent the commercialization of such devices. This economic reality has spurred interest in alternative patterning technologies. One of the leading potential methods is to exploit the self-assembly of block copolymers (BCPs). BCPs are a type of polymer consisting of two or more chemically distinct blocks that are covalently joined together. The components of a BCP can phase-separate, and the resultant features form on the 5 to 50 nm length-scale. This size range is coincidentally ideal for next-generation semiconductor devices. However, BCPs on their own do not immediately form device-relevant features. Processes known collectively as directed self-assembly (DSA) are needed to properly guide BCPs. The work in this dissertation focuses on a very specific class of BCPs, those that contain silicon in just one of the blocks. The presence of silicon in the molecule produces many lithographic advantages, but also requires specialized processing steps. Chapter 1 provides an overview of lithography and block copolymer self-assembly. Chapter 2 introduces the materials and techniques needed to control the behavior of silicon-containing BCPs. Chapter 3 presents and characterizes a variety of silicon-containing BCPs. Last, Chapters 4 and 5 describe two implementations of silicon-containing BCP DSA, one for semiconductor patterning, and the other for hard disk drive applications.Item Design, synthesis, and characterization of functional block copolymers containing fluorinated or hydrophilic segments by ATRP(2008-08) Bucholz, Tracy Laine, 1981-; Loo, Yueh-Lin, 1974-; Sanchez, Isaac C., 1941-Well-defined functional block copolymers containing either a fluorinated or a hydrophilic segment can be synthesized via a controlled free-radical technique, known as atom transfer radical polymerization (ATRP). Their self assembly characteristics in the solid state and in solution were examined in this work with the aim of developing ultralow dielectric constant materials and templates for conductive polymer synthesis, respectively. We demonstrated the controlled synthesis via ATRP of block copolymers containing poly(pentafluorostyrene) (PPFS) and a degradable polymer, such as poly(methyl methacrylate) (PMMA), poly([epsilon]-caprolactone) (PCL), or poly(D,L-lactide) (PLA). These block copolymers microphase separate in the solid state to form periodic nanostructures, such as alternating lamellae, a bicontinuous gyroid on a cubic lattice, cylinders on a hexagonal lattice, or spheres on a body-centered-cubic lattice, depending on the volume fraction of each block and the interblock segregation strength. Additionally, we quantified the interblock segregation strength of PPFS/PMMA, demonstrating that this block copolymer is only approximately twice as segregated as its nonfluorinated counterpart poly(styrene-[beta]-methyl methacrylate) due to the symmetric placement of the polar C-F bonds on the benzene ring in PPFS. We also showed that the self-assembly characteristics of PPFS-containing block copolymers can be used to create nanoporous fluorinated films with ultra-low dielectric constants in the range of 1.7 - 1.9. The dielectric constants are tunable through manipulation of the volume fraction of the degradable block in the parent block copolymers. We also demonstrated the controlled synthesis via ATRP of block copolymers containing poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAAMPSA) with either poly(oligo(ethylene glycol) methyl ether methacrylate) (PEGMA) or poly(methyl acrylate) (PMA). We showed that PEGMA/PAAMPSA formed well-ordered nanostructures in the solid state when cast from strong hydrogen bond accepting solvents, such as DMSO and DMF. PEGMA/PAAMPSA can also be used as the acid dopant in the synthesis of conductive polyaniline (PANI). Additionally, we studied the micelle formation of PMA/PAAMPSA and subsequently used these micelles as templates to create spherical conductive PANI nanoparticles. The size and size distribution of these PANI nanoparticles were dictated by the corresponding characteristics of the micellar template.Item High interaction parameter block copolymers for advanced lithography(2013-12) Cushen, Julia Dianne; Ellison, Christopher J.Block copolymers demonstrate potential in next-generation lithography as a solution for overcoming the limitations of conventional lithographic techniques. Ideal block copolymer materials for this application can be synthesized on a commercial scale, have high [chi]-parameters promoting self-assembly into sub-20 nm pitch domains, have controllable alignment and orientation, and have high etch contrast between the domains for facilitating pattern transfer into the underlying substrate. Block copolymers that contain silicon in one domain are attractive for nanopatterning since they often fulfill at least three of these requirements. However, silicon-containing materials are notoriously difficult to orient in thin films due to the low surface energy of the silicon-containing block, which typically wets the free surface interface. In this work, the methodology behind material choice and the synthesis of new silicon-containing block copolymers by a variety of polymerization techniques will be described. Thin film self-assembly of the block copolymers with domains oriented perpendicular to the plane of the substrate is achieved using different solvent annealing and neutral surface treatments with thermal annealing conditions. Block copolymer patterns are transferred to the underlying substrate by reactive ion etching and directed self-assembly of the polymers is demonstrated using chemical contrast patterns. Interesting thermodynamics governing the self-assembly of block copolymers with solvent annealing will also be discussed. Finally, new amphiphilic block copolymers will be described that were created with lithographic applications in mind but that are most useful for biological applications in drug delivery.Item Modification of surfaces using grafted polymers : a self consistent field theory study(2011-08) Trombly, David Matthew; Ganesan, Venkat; Peppas, Nicholas; Ren, Pengyu; Sanchez, Isaac; Truskett, ThomasThis research focuses on the modeling of surfaces decorated by grafted polymers in order to understand their structure, energetics, and phase behavior. The systems studied include flat and curved surfaces, grafted homopolymers and random copolymers, and in the presence of solvent conditions, homopolymer melt conditions, and diblock copolymer melt conditions. We use self-consistent field theory to study these systems, thereby furthering the development of new tools especially applicable in describing curved particle systems and systems with chemical polydispersity. We study a polymer-grafted spherical particle interacting with a bare particle in a good solvent as a model system for a polymer-grafted drug interacting with a blood protein in vivo. We calculate the energy of interaction between the two particles as a function of grafting density, particle sizes, and particle curvature by solving the self-consistent field equations in bispherical coordinates. Also, we compare our results to those predicted by the Derjaguin approximation. We extend the previous study to describe the case of two grafted particles interacting in a polymer melt composed of chains that are chemically the same as the grafts, especially in the regime where the particle curvature is significant. This is expected to have ramifications for the dispersion of particles in a polymer nanocomposite. We quantify the interfacial width between the grafted and free polymers and explore its correlation to the interactions between the particles, and use simple scaling theories to justify our results. In collaboration with experimentalists, we study the behavior of the glass transition of polystyrene (PS) films on grafted PS substrates. Using the self consistent field theory methods described above as well as a percolation model, we rationalize the behavior of the glass transition as a function of film thickness, chain lengths, and grafting density. Grafting chemically heterogeneous polymers to surfaces in melt and thin film conditions is also relevant for both particle dispersion and semiconductor applications. To study such systems, we model a random copolymer brush in a melt of homopolymer that is chemically identical to one of the blocks. We modify the self-consistent field theory to take into account the chemical polydispersity of random copolymer systems and use it to calculate interfacial widths and energies as well as to make predictions about the window in which perpendicular morphologies of diblock copolymer are likely to form. We also explore the effect of the rearrangement of the chain ends on the surface energy and use this concept to create a simple modified strong stretching theory that qualitatively agrees with our numerical self-consistent field theory results. We explicitly study the system that is most relevant to semiconductor applications - that of a diblock copolymer melt on top of a substrate modified by a random copolymer brush. We explore the morphologies formed as a function of film thickness, grafting density, chain length, and chain blockiness, and make predictions about the effect of these on the neutral window, that is, the range of brush volume fractions over which perpendicular lamellae are expected to occur.Item Physical properties of poly (n-alkyl acrylate) copolymers(2005) O'Leary, Kelly Ann; Paul, Donald R.The physical properties of n-alkyl acrylate copolymers, including thermal characteristics, structure as determined by small angle X-ray scattering, and gas permeability as a function of temperature, were examined in detail and compared to the corresponding homopolymers. Two types of copolymers were examined: those with two crystalline comonomers and those with one crystalline and one non-crystalline comonomer. The crystalline / crystalline copolymers exhibit co-crystallization and, thus, for a given average side-chain length have comparable melting temperatures as the corresponding homopolymers. For a given side-chain length, the copolymers have somewhat lower heats of fusion than the corresponding homopolymers because of a reduction in crystallite size as revealed by SAXS. The crystalline / non-crystalline copolymers do not co-crystallize and experience melting point depression in which the non-crystalline comonomer does not affect the Tm and ∆Hf as much as two crystalline comonomers do. Though not entering the lattice, the non-crystalline comonomers impede the formation of perfect crystals, also reducing the crystallite size, as indicated by SAXS. This depression in crystallinity is reflected in the permeability data for the copolymers. Poly (n-alkyl acrylates) exhibit a ‘jump’ in their gas permeability at the Tm of the side-chain lengths that is mainly caused by a switch in the side-chain morphology from crystalline to amorphous upon melting. The depression in crystallinity for both types of copolymers results in a smaller permeation jump. Interestingly, copolymers containing A10, a comonomer on the border of being crystalline, experience the broadest jump peak. The jump breadth of all copolymers examined correlate with the melting endotherms for these polymers as determined by DSC. Ultimately, the melting endotherms for these copolymer systems provides an excellent tool for predicting permeability changes across the melting region.Item Self-assembly of block coplymer thin films in compressible fluids(2006) Li, Yuan, 1968-; Johnston, Keith P., 1955-; Green, Peter F. (Peter Fitzroy)Item Solvent annealing and thickness control for the orientation of silicon-containing block copolymers for nanolithographic applications(2012-05) Santos, Logan Joseph; Willson, C. G. (C. Grant), 1939-; Ellison, Christopher J.Block copolymers are an ideal solution for a wide variety of nanolithographic opportunities due to their tendency to self-assemble on nanoscopic length scales. High etch selectivity and thin-film orientation are crucial to the success of this technology. Most conventional block copolymers have poor etch selectivity; however, incorporating silicon into one block produces the desired etch selectivity. A positive side effect of the silicon addition is that the χ value (a block-to-block interaction parameter) of the block copolymer increases. This decreases the critical dimension of potential features. Unfortunately, one negative side effect is the increase in the surface energy difference between the blocks. Incorporating silicon decreases the surface energy of that block. Typically, annealing is used to induce the chain mobility that is required for the block copolymer to reach its minimum thermodynamic energy state. Thermal annealing is the easiest annealing technique; however, if the glass transition temperature (Tg) of one block is above the thermal decomposition temperature of the other block, the latter will degrade before the former can reorient. In addition, annealing silicon-containing block copolymers usually results in a wetting layer and parallel orientation since the lower surface energy block favors the air interface, minimizing the free energy. Solvent annealing replaces the air interface with a solvent, thereby changing the surface energy. The solvent plasticizes the block copolymer, effectively decreasing the Tgs of both blocks. Another benefit is the ability to reversibly alter the orientation by changing the solvent or solvent concentration. The challenge with solvent annealing is that it depends on a number of parameters including: solvent selection, annealing time, and vapor concentration, which generate a very large variable space that must be searched to find optimum screening conditions.