Investigation And Optimisation Of The Microphase Separation Of Block Copolymer Thin Films For Use As Nanostructure Scaffolds And Pattern Transfer Masks
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Investigation and Optimisation of the Microphase Separation of Block Copolymer Thin Films for Use as Nanostructure Scaffolds and Pattern Transfer Masks
Upon, self-assembly block copolymers (BCP) form a variety of well-ordered nanometer-sized structures in thin films which satisfy the size requirement for many nanotechnologies. This thesis details the in-depth study of two different BCP systems including the various factors which influence the final film structure, the generation of nanoporous polymer templates and their subsequent use a lithographic etch masks. Chapter 1 provides a general introduction anda brief overview of the reasons for the research into BCP morphologies, the principals of their self-assembly and the potential applications of the systems. Chapter 2 focuses on microphase separation within cylinder-forming polystyrenepoly[ferrocenyldimethylsilane] BCP thin films. Thermal and solvent annealing were both investigated as potential routes to achieve microphase separation. With solvent annealing identified as the superior method, the effect of film thickness on the orientation and stability of the nanoscale structure was investigated. By using the directing effects imposed by topographically patterned substrates, cylindrical structures exhibiting excellent long-range order were achieved. Chapter 3 then summarises several methods of etching these polystyrene- poly[ferrocenyldimethylsilane] films, with reactive ion etching being identified as a rapid route for the generation of poly[ferrocenyldimethylsilane] template structures which can be subsequently used as a positive etch mask for pattern transfer into the underlying substrate. In Chapter 4, polymer brushes were grown from catalytic sites deposited on the substrate. These in-situ brushes were then examined as means of controlling the orientation of lamellar-forming polystyrene-poly(methylmethacrylate) thin films. Also, it was shown that variation of molecular weight of the BCP provides a simple means of controlling resultant feature sizes. The conclusions of all the research presented, as well as the potential future work generated by these results are discussed in Chapter 5. Chapter 6 provides a general overview of the various techniques used during the course of this thesis as well as providing supplementary information on other topics mentioned in previous chapters.
Directed Self-Assembly of Nanostructured Block Copolymer Thin Films Via Dynamic Thermal Annealing
The aggressive miniaturization of nanoelectronic devices poses a pressing challenge in using conventional patterning technologies that are fast approaching their intrinsic resolution limits. Molecular self-assembling block copolymers (BCPs) are promising candidates for integrating and extending the current photolithographic constraints, facilitating the fabrication of next-generation nanotemplating materials via directed self-assembly. The current work focuses on the development of viable dynamic self-assembly strategies for achieving highly ordered versatile BCP nanostructures with precise feature size control and registration, as well as provides insights into the fundamentals of BCP thin film self-assembly driven by dynamic annealing fields A continuous template-free method toward rapid fabrication (2-4 minutes) of highly ordered through-thickness vertical lamellar polystyrene-block-poly(methyl methacrylate) l-PS-b-PMMA) microdomains in l-BCP films on quartz (silicon oxide) substrate was developed. A molecular relaxation induced vertical l-BCP ordering occurs under a transient macroscopic vertical strain field, imposed by a high film thermal expansion rate under sharp thermal gradient cold zone annealing (CZA-S). The high thermal gradient had to be selectively tuned with the CZA-S sweep rates for controlling the polymer chain relaxation dynamics for vertical order. Comparable conventional static thermal annealing of identical l-BCP films using vacuum oven failed to induce the desired nanostructure. Morphology evolution tracked in real time along the CZA-S thermal gradient profile using in situ grazing incidence small angle x-ray scattering (GISAXS) demonstrated four regimes of ordering: microphase separation from a quenched-disordered state (Regime 1), initial formation of vertical lamellae due to the sharp thermal gradient imposed on the l-BCP film (Regime 2), polygrain structure resulting from the broad [del] T region around Tmax (Regime 3), and an ultimate highly vertically ordered l-BCP morphology due to grain coarsening on the cooling edge (Regime 4). A detailed examination of the influence of CZA process parameters such as temperature gradient field strength ([del] T) of the thermal annealing profile, sweep velocity (v) and the corresponding annealing time (t) on the mechanism and dynamics of l-BCP ordering was performed. The complex interplay between thermodynamic equilibrium, surface and interfacial energies, confinement effects and BCP ordering kinetics was also investigated to determine the effect of BCP film attributes on morphological development. By tuning the CZA-S process dynamics with the l-BCP relaxation timescales, this process created vertical l-BCP nanodomains with controlled feature sizes via molecular weight control. Besides regulating the out-of-plane nanostructure orientation, the alignment of BCP microdomains in-plane was locally tuned by biasing the BCP assembly energetics using an edge-templating strategy. The relaxation of residual stresses and minimization of chain distortion energy penalties along the film boundary were the factors governing the edge-templating mechanism that spontaneously aligns the BCP microdomains orthogonal to the film-discontinuity. Both, kinetic and thermodynamic factors were associated with the boundary-propagation effect. This research demonstrates a new paradigm for advancement of BCP nanotemplating and nanolithography applications due to its potential to fabricate user-defined hierarchical micro-nanopatterns.
Block Copolymer Thin Films for Nanometer Pattern Generation and Nanostructure Synthesis
This dissertation, "Block Copolymer Thin Films for Nanometer Pattern Generation and Nanostructure Synthesis" by Hai, Wang, 王海, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled BLOCK COPOLYMER THIN FILMS FOR NANOMETER PATTERN GENERATION AND NANOSTRUCTURE SYNTHESIS submitted by HAI WANG for the Degree of Doctor of Philosophy at The University of Hong Kong in August 2006 Block copolymers show great potential in nanofabrication, therefore, studies of self assembly in block copolymers and their application for nanostructure synthesis are of considerable interest. The self assembly of asymmetric di- block copolymer poly(styrene ethylene oxide) and poly(styrene-block-methyl methacrylate)thin...lmsisstudiedinthisthesisandtheapplicationofpoly(styrene ethyleneoxide) as astructuredirectingagent inthe synthesis of mesoporous ti- tania structure is also investigated. Firstly, factors aecting the self assembly were systemically examined for thin ...lms of two asymmetric diblock copolymers: poly(styrene-block-methyl methacrylate)(P(S-b-MMA))andpoly(styreneethyleneoxide)(P(S-b-EO)).ItwasfoundthatthemorphologyofP(S-b-MMA)isstronglythicknessdependent. Five representative morphologies are identi...ed. Contrary to generally-accepted concept, themorphologywithperpendicularPMMAcylindersinPSmatrixwas obtained for the ...lm thickness range of 48 nm to 63 nm on SiOx/Si substrates withoutapplyingexternalelectric...eldoranysurfacetreatment(hydrogenpas- sivation, functionalizedrandomcopolymers, orself-assembledmonolayers). The ...lms with uniform ordering at large scale can be obtained after annealing by choosing the proper spinning speed, solution concentration, substrate cleaning procedure, and annealing conditions. On the other hand, P(S-b-EO) thin ...lms donotexhibitthicknessdependenceofthemorphology. Perpendicularcylinders were obtained in all cases. Therefore, P(S-b-EO) has been chosen as a model system for comprehensive studies of factors aecting phase contrast in tapping modeatomicforcemicroscopy. Thecorrelationbetweenthephasecontrastand the elasticity of PEO domains and PS matrix in the poly(styrene ethylene ox- ide) thin ...lmwas established and explained with the energy dissipation theory. The phase contrast was also found to be dependent on the atomic force mi- croscope used due to dierent methods of detecting phase contrast in dierent microscopes. After detailed characterization of P(S-b-EO), this diblock copolymer was used as the structure directing agent for the synthesis of mesoporous titania nanostructures. The developed method for titania synthesis is simple and highly reproducible. The morphologies of the mesoporous titania structures can be controlled by titania precursor concentration, diblock copolymer P(S- b-EO), solvents and annealing conditions. The thermally stable mesoporous titania structure was used in heterojunction solar cells with device structure ITO/Titania/MEH-PPV/Au. The short circuit current densities of the solarcellswereimprovedoverthepreviousreports, whichcanbeattributedtobetter conjugatedpolymer...llingandincreasedchargecarrierpercolationpathsinthe bicontinuous titania mesostructure with large pore size. DOI: 10.5353/th_b3697984 Subjects: Copolymers Thin films Nanostructured materials - Synthesis