Brian G. Landes

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.

Monofilament drawing device for in situ x‐ray scattering studies of orientation development in polymeric fibers

The physical properties of polymer fibers are directly related to the development of orientation in the draw zone under extensional conditions. Although the final properties and microstructure of fibers can be evaluated after processing is completed, it is desirable to understand the development of orientation during drawing independently from the effects superimposed by subsequent unit operations. In situ x‐ray scattering measurements of the extrudate in the draw zone provide an ideal means of accomplishing this goal. Depending on the polymeric system to be studied, rotating anode or synchrotron‐based x‐ray sources may be required, making portability of the fiber drawing device highly desirable. This paper describes an easily transportable in situ x‐ray filament drawing device, and discusses typical data obtained using the device to produce filaments from a liquid crystalline nematic solution of poly(cis‐benzoxazole) in polyphosphoric acid.

Synthesis and characterization of urea-based polyureas: 2. Morphology control in urea-terminated poly(1,6-hexamethyleneurea) particles

Abstract The effects of reaction parameters on the synthesis of urea-terminated poly(1,6-hexamethyleneurea) particles dispersed in a polyol continuous phase have been studied. Oligomeric units are held together by hydrogen bonding into a macrostructure which separates as a stable dispersed phase during synthesis. Monomer addition rate, synthesis temperature and stirring rate are important factors in morphology control of the particles. High aspect ratio (10–20) particles having a spiral fibre bundle morphology (by scanning electron microscopy) are produced at synthesis temperature between 140 and 175°C; spherical particles are produced at 185°C. Particles produced at 140°C have a different crystalline structure from particles produced at higher temperatures. Molecular weight, particle size and the extent of hydrogen bonding increase with increasing synthesis temperature. The structure of these highly crystalline particles is established at an early stage in the reaction. Annealing up to 185°C has little effect on particle morphology. Annealing near the melting point (270°C) results in loss of crystallinity; particle macrostructure is destroyed by melting or dissolution.

High-Modulus Low-Cost Carbon Fibers from Polyethylene Enabled by Boron Catalyzed Graphitization

Currently, carbon fibers (CFs) from the solution spinning, air oxidation, and carbonization of polyacrylonitrile impose a lower price limit of ≈

High-temperature tensile cell for in situ real-time investigation of carbon fibre carbonization and graphitization processes

10 per lb, limiting the growth in industrial and automotive markets. Polyethylene is a promising precursor to enable a high-volume industrial grade CF as it is low cost, melt spinnable and has high carbon content. However, sulfonated polyethylene (SPE)-derived CFs have thus far fallen short of the 200 GPa tensile modulus threshold for industrial applicability. Here, a graphitization process is presented catalyzed by the addition of boron that produces carbon fiber with >400 GPa tensile modulus at 2400 °C. Wide angle X-ray diffraction collected during carbonization reveals that the presence of boron reduces the onset of graphitization by nearly 400 °C, beginning around 1200 °C. The B-doped SPE-CFs herein attain 200 GPa tensile modulus and 2.4 GPa tensile strength at the practical carbonization temperature of 1800 °C.

The Structural Evolution of Pore Formation in Low‐k Dielectric Thin Films

A new high-temperature fibre tensile cell is described, developed for use at the Advanced Photon Source at Argonne National Laboratory to enable the investigation of the carbonization and graphitization processes during carbon fibre production. This cell is used to heat precursor fibre bundles to temperatures up to ∼2300°C in a controlled inert atmosphere, while applying tensile stress to facilitate formation of highly oriented graphitic microstructure; evolution of the microstructure as a function of temperature and time during the carbonization and higher-temperature graphitization processes can then be monitored by collecting real-time wide-angle X-ray diffraction (WAXD) patterns. As an example, the carbonization and graphitization behaviour of an oxidized polyacrylonitrile fibre was studied up to a temperature of ∼1750°C. Real-time WAXD revealed the gradual increase in microstructure alignment with the fibre axis with increasing temperature over the temperature range 600-1100°C. Above 1100°C, no further changes in orientation were observed. The overall magnitude of change increased with increasing applied tensile stress during carbonization. As a second example, the high-temperature graphitizability of PAN- and pitch-derived commercial carbon fibres was studied. Here, the magnitude of graphitic microstructure evolution of the pitch-derived fibre far exceeded that of the PAN-derived fibres at temperatures up to ∼2300°C, indicating its facile graphitizability.

Melt and Solid-State Structures of Polydisperse Polyolefin Multiblock Copolymers

Specular x‐ray reflectivity and small angle neutron scattering were used to characterize changes in the porosity, pore size and pore size distribution on processing a polymeric low‐k material filled with 21.6 volume percent of a deuterated porogen with an average radius of 56 A. Processing yielded a decrease in porosity to about 11 %, an increase in average pore radius to 83 A, and a narrower pore size distribution. A sample with an unusual pore structure could be easily identified.