Daniel J. Murray

Real-time cryo-deformation of polypropylene and impact-modified polypropylene in the transmission electron microscope☆

Abstract Dynamic plane-stress failure has been observed directly in the transmission electron microscope as a function of temperature using a commercially available cooling/straining holder in conjunction with a copper deformation cartridge. The low-temperature cooling stage permits studies of the ductile-brittle transition when the transition is between + 23 and − 170°C. A change in deformation mode was observed on the submicrometre level for polypropylene and impact-modified polypropylene. At room temperature, polypropylene and impact-modified polypropylene deform by shear yielding. Below the ductile-brittle transition the polymer chain mobility is curtailed and crazing dominates. The stage allows observation of the deformation at varying temperature, and events occurring during the deformation can be recorded in real time using a CCD camera.

Designing new materials and processes for directed self-assembly applications

Directed self-assembly (DSA) of block copolymers (BCPs) is a promising technology for advanced patterning at future technology nodes, but significant hurdles remain for commercial implementation. The most widely studied material for DSA is poly(styrene-block-methyl methacrylate) (PS-PMMA), but this material has a relatively weak segregation strength that has limited its utility to patterns above 24 nm pitch. This paper reports on some of Dows efforts to develop new materials capable of extending DSA to smaller pitch by development of new BCP copolymer materials with stronger segregation strength. Some preliminary efforts are reported on new substrate treatments that stabilize perpendicular orientations in a high-χ block copolymer that also incorporate an etch-resistant block to facilitate patterning at small dimensions. In addition, development of new block copolymer materials that have a χ-parameter that is large enough to drive defect reduction and but not so high that it precludes thermal annealing are also presented. DSA of these new materials is demonstrated using thermal annealing processes at pitch ranging from 40 to 16 nm, and etch capability is also demonstrated on a material with 18 nm pitch. These technologies hold promise for the extension of DSA to sub 24 nm pitch.

New materials and processes for directed self-assembly

Directed self-assembly (DSA) of block copolymers (BCPs) is a promising technology for advanced patterning at future technology nodes, but significant hurdles remain for commercial implementation. The most widely studied material for DSA is poly(styrene-block-methyl methacrylate) (PS-PMMA), but the relatively weak segregation strength of PSPMMA results in some limitations. This paper reports on these limitations for PS-PMMA and highlights a path to success through use of more strongly segregated “high-χ” block copolymers. In general, stronger segregation is predicted to lower defectivity at equilibrium, but unfortunately, kinetics of self assembly also becomes much slower as segregation strength increases. Recognizing diffusion is much faster for cylinder morphologies than lamellar ones, we have investigated new cylinder-forming BCPs that enable defect elimination with thermal annealing processes. In addition, a formulation strategy is presented that further improves the kinetics of the assembly process, enabling tremendous improvements in defectivity over simple BCP systems. Excitingly, successful chemoepitaxy DSA with a high-χ lamellar BCP is also demonstrated using a thermal annealing process and no top coat. These technologies hold promise to enable DSA with thermal annealing processing across pitches from 40 - 16 nm.