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

The controlled, ring-opening polymerisation of DL-lactide in supercritical carbon dioxide (scCO(2)) 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 H-1 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 scCO(2) is conducted at temperatures much lower than that required for bulk polymerisation of LA

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 SEMI 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

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

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

Electron-beam-induced freezing of a positive tone EUV resist for use in 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