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Pattern Formation and Phase Behavior in PS-B-SI Containing Block Copolymer Thin Film

Hsieh, I-Fan
http://rave.ohiolink.edu/etdc/view?acc_num=akron1364835896

Abstract Details

2013, Doctor of Philosophy, University of Akron, Polymer Science.
Since the top-down approaches, such as the extremely ultraviolet (EUV) technique and the high-index fluid-based immersion ArF lithography, may be cover one or two generations, these lithography technologies are getting more severe for the feature size scaling down to sub 10 nm. The directed self-assembly technology of block copolymers is one of the candidates for next generation lithography which can afford feature sizes that are dictated by the molecular weight of the block copolymer and are typically 15 to 30 nm. Directed self-assembly of block copolymers has attracted attention as a technology to extend photoresist-based lithography to smaller dimensions. It has been demonstrated that the directed self assembly of block copolymer offers a new route to perfect nanolithographic pattering at sub-50 nm length scale with molecular scale precision. For application in electronic media, it requires large-area, long-range ordered structures, which is both a kinetic and thermodynamic problem and requires subtle balance of various parameters and processing conditions. So far, block copolymer thin films have already achieved certain success, mainly with higher molecular weights and a feature size of ~30 nm. Several challenges still remain, such as (a) the generation of long-range ordered structure with smaller feature sizes (domain size < 22 nm), (b) iv obtaining sharp interface between two domains with high lithographic contrast, particularly for smaller feature sizes, and (c) etch selectivity and resistance between two phases in the nanostructure. To address these challenges, several different approaches have been used in our research. First approach is using PS-b-PDMS. PDMS-containing block copolymers have emerged as next generation block copolymers for nanolithography. Their films can be processed under dry conditions using oxygen plasma to produce inorganic, silica patterns which enables their integration into existing device fabrication. Also, the large thermodynamic incompatibility of silicon-containing polymers with other organic polymers is favorable for patterns with small domains sizes, large correlation lengths, and low interfacial roughness. In PS-b-PDMS system, a solvent-induced spherical structure was obtained and stabilized by preparing both the bulk and thin film from propylene glycol methyl ether acetate (PGMEA) solvent. Unlike other block copolymer thin film systems, this solvent induced spherical structure possesses very high meta-stability and can be stabilized during thermal annealing up to 200 oC. This unusual high meta-stability can be attributed to the large ¿ value between PS and PDMS blocks thus result in a high energy barrier for morphology transition. In the contrast, a unique structure evolution route was observed during solvent treatments. Under a controlled vapor of PS selective solvent annealing, install of a direct transition from the metastable spherical structure to the equilibrium cylindrical structure, an oscillation of the structural transition between spheres and cylinders was observed in the thin film state. The kinetics of this oscillation of structural transition was found to be closely related to the solvent vapor concentration v and film thickness. This experiment revealed a unique ordering pathway towards the equilibrium structure in the thin film for this PS-b-PDMS diblock copolymer. Another approach to address the issues is utilizing the self-assembly of a class of shape amphiphiles. Shape amphiphiles refer to a class of asymmetric nano-entities molecules possessing amphiphilic features based on differences in the shape of the molecular segments. Shape amphiphiles are capable of self-assembling into hierarchical structures that can cover the feature sizes of sub-10 nm, which is relatively hard to achieve by traditional coil-coil block copolymer system. A series of PS-tethered hydrophilic POSS thin films with different PS molecular weight were studied here and an interesting result was found in PS-POSS thin film system with cylindrical phase. GISAXS experiments proved that a special metastable phase with compressed packed symmetry was found in PS-POSS thin film system with parallel cylinder morphology after solvent annealing process, and this metastable phase was found in both PS-APOSS and PS-DPOSS thin film system regardless of the film thickness and solvent properties used during annealing. The phase behavior of coil-coil block-copolymers is thermodynamically controlled by the conformational entropies of two blocks and the interfacial energy. On the contrary, giant shape amphiphiles are consisted of particles and polymer chains. There is no conformational entropy for particles, and the interfacial energy is different from the block-copolymer cases. The polymer chains in giant shape amphiphiles also show more stretched near interface compared to block-copolymers. These unique properties make vi giant shape amphiphiles a new field to study. A further study of the phase transition found that the transition pathway is highly depending on the method of thermal treatment and two very unique transitions were found during continuous heating and isothermal annealing processes. During continuous heating, metastable compressed packing phase transferred to parallel cylinder with short range order packing and then transferred to thermodynamic equilibrium hexagonal packing parallel cylinder phase. On the other hand, an oscillation transition between compressed packed symmetry and hexagonal packed cylinder was found during isothermal annealing process.
Stephen Cheng, Dr. (Advisor)
Ali Dhinojwala, Dr. (Committee Member)
Darrell Reneker, Dr. (Committee Member)
Toshikazu Miyoshi, Dr. (Committee Member)
Kevin Cavicchi, Dr. (Committee Member)
Polymers
block copolymer thin film; GISAXS; pattern

Recommended Citations

Citations

  • Hsieh, I.-F. (2013). Pattern Formation and Phase Behavior in PS-B-SI Containing Block Copolymer Thin Film [Doctoral dissertation, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1364835896

    APA Style (7th edition)

  • Hsieh, I-Fan. Pattern Formation and Phase Behavior in PS-B-SI Containing Block Copolymer Thin Film . 2013. University of Akron, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1364835896.

    MLA Style (8th edition)

  • Hsieh, I-Fan. "Pattern Formation and Phase Behavior in PS-B-SI Containing Block Copolymer Thin Film ." Doctoral dissertation, University of Akron, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=akron1364835896

    Chicago Manual of Style (17th edition)

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