Yoshihito Ishida

One-Step Direct-Patterning Template Utilizing Self-Assembly of POSS-Containing Block Copolymers.

We report the self-assembly of organic-inorganic block copolymers (BCP) in thin-films by simple solvent annealing on unmodified substrates. The resulting vertically oriented lamellae and cylinders are converted to a hard silica mask by a single step highly selective oxygen plasma etching. The size of the resulting nanostructures in the case of cylinders is less than 10 nm.

Directed Self-Assembly of Triblock Copolymer on Chemical Patterns for Sub-10-nm Nanofabrication via Solvent Annealing

Directed self-assembly (DSA) of block copolymers (BCPs) is a leading strategy to pattern at sublithographic resolution in the technology roadmap for semiconductors and is the only known solution to fabricate nanoimprint templates for the production of bit pattern media. While great progress has been made to implement block copolymer lithography with features in the range of 10-20 nm, patterning solutions below 10 nm are still not mature. Many BCP systems self-assemble at this length scale, but challenges remain in simultaneously tuning the interfacial energy atop the film to control the orientation of BCP domains, designing materials, templates, and processes for ultra-high-density DSA, and establishing a robust pattern transfer strategy. Among the various solutions to achieve domains that are perpendicular to the substrate, solvent annealing is advantageous because it is a versatile method that can be applied to a diversity of materials. Here we report a DSA process based on chemical contrast templates and solvent annealing to fabricate 8 nm features on a 16 nm pitch. To make this possible, a number of innovations were brought in concert with a common platform: (1) assembling the BCP in the phase-separated, solvated state, (2) identifying a larger process window for solvated triblock vs diblock BCPs as a function of solvent volume fraction, (3) employing templates for sub-10-nm BCP systems accessible by lithography, and (4) integrating a robust pattern transfer strategy by vapor infiltration of organometallic precursors for selective metal oxide synthesis to prepare an inorganic hard mask.

Alkylated cage silsesquioxanes: a comprehensive study of thermal properties and self-assembled structure

Derivations of mono-substituted polyhedral oligomeric silsesquioxanes (POSS) with long aliphatic chains were synthesized and self-assembled structures were investigated. The effects of the alkyl chain length and branching on the thermal self-assembling behaviors of the POSS derivatives were examined by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). In addition, small- and wide-angle X-ray scattering (SAXS/WAXS) as well as transmission electron microscopy (TEM) were employed to elucidate their self-assembled morphologies. Long-range straight ordered lamellar structures with sharp boundaries could be reliably formed in the bulk samples of alkylated cage silsesquioxanes by thermal annealing. Furthermore, this research demonstrates an approach to precisely control the feature size at the nanometer scale by carefully tuning parameters of alkyl chain length and branching number.

Synthesis, end-functionalization and characterization of hyperbranched polysiloxysilanes from AB3 type monomer

Hyperbranched polysiloxysilanes (HBPSs), with a variety of terminal functional groups (vinyl, epoxy, carboxyl and hydroxyl), were synthesized by the self-polymerization of an AB3 type monomer of tris(dimethylvinylsiloxy) silane, with subsequent end-functionalizations, such as epoxidation and radical addition reaction, respectively. The ratio of the α- and β-addition linkages in the HBPS polymerized by hydrosilylation of the AB3 monomer was found to be approximately 1 to 3. The thermal stability and solubility were affected by the terminal functional groups.

Improved lithography by directed self-assembly of ultra-high-density patterns

Innovative lithographic processes are critical to continue shrinking semiconductor devices beyond the 22nm node, and to enable new devices with nanometer-scale features. Although photolithography is the industry standard, resolution requirements have reached beyond the wavelength of light. Consequently, it is becoming increasingly complicated and expensive to further minimize feature dimensions. Among the available lithographic alternatives, self-assembling processes have received much attention. Directed self-assembly (DSA) of block copolymers on chemically patterned templates is one promising route to obtaining patterns with sub-photolithographic resolution. This material consists of immiscible polymers that are joined end to end. They exhibit a wide variety of structures (morphologies) by virtue of microphase separation, including ordered arrays of lamellar (layered), cylindrical, and spherical microdomains in the equilibrium configuration. The morphologies depend on the relative volume fraction of the constituent polymers and on temperature, whereas the sizes of the structures depend on their molecular weight. The typical size of the microdomains is a few tens of nanometers, which makes that system typically attractive for lithographic application.1 A large body of work has been done in this field using poly(styrene-block-methylmethacrylate) (PS-bPMMA) as a phase-segregating material.2–7 However, because low molecular weight PS-b-PMMA is a weakly segregating system, the minimum dimension achievable is about 20–25nm full pitch. Although various higher-segregating block copolymer systems have been proposed to overcome this size limitation,8–10 Figure 1. Chemical structure of poly(methyl methacrylate-blockmethacrylate polyhedral oligomeric silsesquioxane) (PMMA-bPMAPOSS). Si: Silicon. m, n: Degree of polymerization.

Synthesis of diblock copolymers consisting of POSS-containing random methacrylate copolymers and polystyrene and their cross-linked microphase-separated structure via fluoride ion-mediated cage scrambling

Synthesis of a series of diblock copolymers consisting of POSS-containing random methacrylate copolymers and polystyrene (P(MAPOSS-r-methyl methacrylate)-b-polystyrene etc.) has been established by reversible addition–fragmentation chain-transfer (RAFT) polymerisation. The polymerisation of styrene as the second block was well controlled when POSS-containing random copolymers were used as the chain transfer agent (CTA). Dynamic cross-linking of POSS-containing block copolymers, which utilized a cage scrambling reaction among pendant POSS units mediated by a fluoride ion, was achieved by evaporating the solvent from a solution of block copolymers tetrabutylammonium fluoride (TBAF) and 1,4-bis(triethoxysilyl)benzene (BTSB) in THF. During the solvent evaporation and thermal annealing that provided cross-linked polymer films, a phase-separated structure was formed. The microphase-separated structure of the cross-linked block copolymers showed the cylindrical morphology of the POSS-containing blocks, which was proved by small angle X-ray scattering (SAXS) measurements and transmission electron microscopy (TEM) observations. A clear microphase-separated structure was obtained when a larger amount of fluoride ions was used for cage scrambling. The morphology was maintained even after immersing in tetrahydrofuran, indicating that the phase-separated structure was completely immobilized by cross-linking.