Anguang Yu

Control of the orientation of symmetric poly(styrene)-block-poly(D,L-lactide) block copolymers using statistical copolymers of dissimilar composition

The interactions of block copolymers with surfaces can be controlled by coating those surfaces with appropriate statistical copolymers. Usually, a statistical copolymer comprised of monomer units identical to those of the block copolymer is used; that is, typically a poly(styrene)-stat-poly(methyl methacrylate) (PS-stat-PMMA) is used to direct the alignment of poly(styrene)-block-poly(methyl methacrylate) (PS-block-PMMA), and poly(styrene)-stat-poly(2-vinylpyridine) (PS-stat-P2VP) has been used for poly(styrene)-block-poly(2-vinylpyridine) (PS-block-P2VP). Reports of controlling the orientation of block copolymers with statistical copolymers with a dissimilar composition are limited. Here, we demonstrate that this method can be further extended to show that PS-stat-PMMA can be used to control the wetting properties of poly(styrene)-block-poly(D,L-lactide) (PS-block-PDLA). Surfaces were modified with a series of cross-linked PS-stat-PMMA-stat-glycidyl methacrylate terpolymers, and the surface chemistries and energies were assessed using angle-dependent X-ray photoelectron spectroscopy and the two-liquid harmonic method, respectively. From these experiments, an expected neutral compositional window was identified for symmetrical PS-block-PDLA. Moreover, high-resolution SEM, AD-XPS, and grazing-incidence SAXS measurements were used to evaluate the morphology of PS-block-PDLA as a function of the surface composition of the underlying cross-linked copolymer films, and the neutral composition was found to range from 32 to 38 mol % of PS, in the bulk polymer. Ultimately, we demonstrated the determination of nonpreferential surface compositions that allow the self-assembly of lamellae with sizes in the sub-10 nm regime that are oriented perpendicular to the substrate. These findings have important implications for the use of PS-block-PDLA block copolymers in directed self-assembly, most specifically in advanced lithographic processes.

Controlled polymerisation of lactide using an organo-catalyst in supercritical carbon dioxide

The controlled, ring-opening polymerisation of DL-lactide in supercritical carbon dioxide (scCO2) using benzyl alcohol as an initiator and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as an organo-catalyst, is reported. Despite reports of DBU being efficiently converted to a carbonate salt in the presence of a proton source, it was found that DBU was still an efficient catalyst for the ring opening polymerisation of DL-lactide. Matrix-assisted laser desorption ionisation time of flight mass spectroscopy and 1H nuclear magnetic resonance analysis demonstrated that end-group fidelity was maintained on the resulting polymer and significant transesterification was not observed under anhydrous conditions. We report a truly ‘green’ process for the synthesis of polylactic acid (PLA) with the total absence of potentially toxic organic solvents and inorganic catalysts. In addition, the reaction in scCO2 is conducted at temperatures much lower than that required for bulk polymerisation of LA.

EUVL compatible LER solutions using functional block copolymers

Directed self assembly (DSA) of block copolymers is an emerging technology for achieving sub-lithographic resolution. We investigate the directed self assembly of two systems, polystyrene-block-poly-DL-lactic acid (PS-b-PDLA) and PSb- poly(methyl methacrylate). For the PS-b-PDLA system we use an open source EUVL resist and a commerciallyavailable underlayer to prepare templates for DSA. We investigate the morphology of the phase separated domains and compare the LER of the resist and the PS-PDLA interface. For the PS-b-PMMA system we again use an open source resist, but the annealing conditions in this case require crosslinking of the resist prior to deposition of the block copolymer. For this system we also investigate the morphology of the phase separated domains and compare the LER of the resist and the PS-PMMA interface.

Patterning of tailored polycarbonate based non-chemically amplified resists using extreme ultraviolet lithography

A series of high-performance polycarbonates have been prepared with glass-transition temperatures and decomposition temperatures that are tunable by varying the repeat-unit chemical structure. Patterning of the polymers with extreme UV lithography has been achieved by taking advantage of direct photoinduced chain scission of the polymer chains, which results in a molecular-weight based solubility switch. After selective development of the irradiated regions of the polymers, feature sizes as small as 28.6 nm have been printed and the importance of resist-developer interactions for maximizing image quality has been demonstrated.

Development of Polymers for Non-CAR Resists for EUV Lithography

Three strategies for approaching the design and synthesis of non-chemically amplified resists (non-CARs) are presented. These are linear polycarbonates, star polyester-blk-poly(methyl methacrylate) and comb polymers with polysulfone backbones. The linear polycarbonates were designed to cleave when irradiated with 92 eV photons and high Tg alicyclic groups were incorporated into the backbone to increase Tg and etch resistance. The star block copolymers were designed to have a core that is sensitive to 92 eV photons and arms that have the potential to provide properties such as high Tg and etch resistance. Similarly the polysulfone comb polymers were designed to have an easily degradable polymer backbone and comb-arms that impart favorable physical properties. Initial patterning results are presented for a number of the systems.

Polycarbonate based nonchemically amplified photoresists for extreme ultraviolet lithography

Some initial EUVL patterning results for polycarbonate based non-chemically amplified resists are presented. Without full optimization the developer a resolution of 60 nm line spaces could be obtained. With slight overexposure (1.4 × E0) 43.5 nm lines at a half pitch of 50 nm could be printed. At 2x E0 a 28.6 nm lines at a half pitch of 50 nm could be obtained with a LER that was just above expected for mask roughness. Upon being irradiated with EUV photons, these polymers undergo chain scission with the loss of carbon dioxide and carbon monoxide. The remaining photoproducts appear to be non-volatile under standard EUV irradiation conditions, but do exhibit increased solubility in developer compared to the unirradiated polymer. The sensitivity of the polymers to EUV light is related to their oxygen content and ways to increase the sensitivity of the polymers to 10 mJ cm-2 is discussed.

Electron-Beam-Induced Freezing of an Aromatic-Based EUV Resist: A Robust Template for Directed Self-Assembly of Block Copolymers

Resist freezing is routinely used in lithography applications to facilitate double patterning and the directed self-assembly (DSA) of block copolymers. Previous reports of graphoepitaxy within patterned positive-tone resists used chemical freezing agents which are known to cause significant shrinkage of critical dimensions (CD). We report the “freezing” of an aromatic-based extreme ultraviolet resist by exposure to an electron beam, so did not require the use of chemical agents. Crucially, the process did not lead to significant changes in CD and line edge roughness, where the “frozen” patterns were resistant to treatment with solvents and annealing to temperatures well above the glass transition temperature of the uncrosslinked resist. Finally, we take advantage of these properties and demonstrate the utility of this process for applications in the DSA of block copolymers leading to pattern multiplication.

Electron beam induced freezing of positive tone, EUV resists for directed self assembly applications

The commercialization of 32 nm lithography has been made possible by using double patterning, a technique that allows for an increased pattern density, potentially, through resist freezing and high precision pattern registration. Recent developments in directed self assembly (DSA) also uses resist freezing for stabilizing positive tone resists used in graphoepitaxy. We have developed a method of patterning an open source, positive tone EUV resist using electron beam lithography (EBL), and studied a novel way of freezing a positive tone EUV photoresists through electron beam induced crosslinking. Through metrological analysis, crosslinked pattern was observed to retain consistent critical dimensions (CD) and line-edge roughness (LER) after they were annealed at temperatures higher than the glass transition of the photoresist. This process has been used to freeze patterned EUV photoresists, which have been subsequently used for directed self assembly of PS-b-PMMA and has potential applications in double patterning in an LFLE scenario.

Mechanism of hydrogenation of [60]fullerene with Zn-conc. HCl

A plausible mechanism for hydrogenation of [60]fullerene with Zn-conc. HCl is given and it is confirmed by synthesis of C60H36 by reaction of [60]fullerene and Zn–ZnCl2–H2O.

Hydrogen Bonding Self‐Assembly of Functionalized [60]Fullerene with a Barbituric Acid Derivative

Abstract A new supramolecular system of functionalized [60]fullerene bearing one 2,6‐diaminopyridine moiety with a barbituric acid derivative was constructed through six‐point hydrogen‐bonding interaction. The self‐assembly systems were studied by 1H NMR, UV‐Vis spectra, and a SEM image.