Brian K. Long

A Robust Ni(II) α-Diimine Catalyst for High Temperature Ethylene Polymerization

Sterically demanding Ni(II) α-diimine precatalysts were synthesized utilizing 2,6-bis(diphenylmethyl)-4-methyl aniline. When activated with methylaluminoxane, the catalyst NiBr2(ArN═C(Me)-C(Me)═NAr) (Ar = 2,6 bis(diphenylmethyl)-4-methylbenzene) was highly active, produced well-defined polyethylene at temperatures up to 100 °C (Mw/Mn = 1.09-1.46), and demonstrated remarkable thermal stability at temperatures appropriate for industrially used gas-phase polymerizations (80-100 °C).

Relationship between nanoscale roughness and ion-damaged layer in argon plasma exposed polystyrene films

The uncontrolled development of nanoscale roughness during plasma exposure of polymer surfaces is a major issue in the field of semiconductor processing. In this paper, we investigated the question of a possible relationship between the formation of nanoscale roughening and the simultaneous introduction of a nanometer-thick, densified surface layer that is formed on polymers due to plasma damage. Polystyrene films were exposed to an Ar discharge in an inductively coupled plasma reactor with controllable substrate bias and the properties of the modified surface layer were changed by varying the maximum Ar+ ion energy. The modified layer thickness, chemical, and mechanical properties were obtained using real-time in situ ellipsometry, x-ray photoelectron spectroscopy, and modeled using molecular dynamics simulation. The surface roughness after plasma exposure was measured using atomic force microscopy, yielding the equilibrium dominant wavelength λ and amplitude A of surface roughness. The comparison of mea...

Materials for step and flash imprint lithography (S-FIL®)

Step and flash imprint lithography, or S-FIL®, was introduced in 1999 by The University of Texas at Austin (Proc. SPIE-Int. Soc. Opt. Eng., 1999, 3676, 379), and has progressed from an academic curiosity to commercialization in less than five years (J. Microlithogr., Microfabr., Microsyst., 2005, 4, 1). It has proven to be a cost effective, high resolution alternative to traditional optical lithography and has been placed on The International Technology Roadmap for Semiconductors (ITRS) as a potential candidate for 32 nm device fabrication (http://www.itrs.net/Links/2006Update/FinalToPost/08_Lithography2006Update.pdf.). This article summarizes the efforts made towards the development of imprint materials for S-FIL and the obstacles that have yet to be overcome.

Semi-Crystalline Polar Polyethylene: Ester-Functionalized Linear Polyolefins Enabled by a Functional-Group-Tolerant, Cationic Nickel Catalyst.

A dibenzobarrelene-bridged, α-diimine Ni(II) catalyst (rac-3) was synthesized and shown to have exceptional behavior for the polymerization of ethylene. The catalyst afforded high molecular weight polyethylenes with narrow dispersities and degrees of branching much lower than those made by related α-diimine nickel catalysts. Catalyst rac-3 demonstrated living behavior at room temperature, produced linear polyethylene (Tm =135 °C) at -20 °C, and, most importantly, was able to copolymerize ethylene with the biorenewable polar monomer methyl 10-undecenoate to yield highly linear ester-functionalized polyethylene.

Study of ion and vacuum ultraviolet-induced effects on styrene- and ester-based polymers exposed to argon plasma

Plasma-polymer interactions are important for the purpose of etching, deposition, and surface modification in a wide range of different fields. An Ar discharge from an inductively coupled plasma reactor was used to determine the factors in a simple plasma that control etch and surface roughness behavior for three styrene-based and three ester-based model polymers. The authors compared the etch behavior of polymers in Ar plasma discharges with low and high energy ions by changing the substrate bias, compared cooled and elevated substrate temperature conditions, and compared fully plasma-exposed conditions and vacuum ultraviolet (vuv)-only conditions by employing a magnesium fluoride window to prevent ion bombardment in the vuv-only case. It was found that ions, vuv radiation, and temperature all had significant impact on the etch behavior of polymers. The dependence of polymer structure on etch and surface roughness was also compared. Polymers with styrene and ester side groups were compared and polymers w...

Near-surface modification of polystyrene by Ar+: Molecular dynamics simulations and experimental validation

Results are presented from molecular dynamics (MD) simulations of 100eV Ar+ bombardment of a model polystyrene (PS) surface. The simulations show that the system transitions from an initially high sputter yield (SY) for the virgin polymer to a drastically lower SY as steady state is approached. This is consistent with corresponding ion beam experiments. The MD indicates that this drop in SY is due to the formation of a heavily cross-linked, dehydrogenated damaged layer. The thickness and structure of this layer are also consistent with ellipsometry and x-ray photoelectron spectroscopy measurements of Ar plasma-exposed PS samples.

Design of Reversible Cross-Linkers for Step and Flash Imprint Lithography Imprint Resists

Progress in the semiconductor manufacturing industry depends upon continuous improvements in the resolution of lithographic patterning through innovative materials development and frequent retooling with expensive optics and radiation sources. Step and Flash Imprint Lithography is a low-cost, nanoimprint lithography process that generates nanopatterned polymeric films via the photopolymerization of low-viscosity solutions containing cross-linking monomers in a transparent template (mold). The highly cross-linked imprint materials are completely insoluble in all inert solvents, which poses a problem for reworking wafers with faulty imprints and cleaning templates contaminated with cured imprint resist. Degradable cross-linkers provide a means of stripping cross-linked polymer networks. The controlled degradation of polymers containing acetal- and tertiary ester-based cross-linkers is demonstrated herein. The viscosity and dose to cure are presented for several prepolymer formulations, along with imprint resolution and tensile modulus results for the cured polymers. Optimum conditions for de-cross-linking and stripping of the cross-linked polymers are presented, including demonstrations of their utility.

Fundamental Optical Properties of Linear and Cyclic Alkanes: VUV Absorbance and Index of Refraction

VUV absorbance and index of refraction data for a series of linear and cyclic alkanes have been collected in order to understand the relationship between the electronic excitation wavelength (or absorbance edge), index of refraction, and molecular structure. The absorbance edge and index for a homologous series of both linear and cyclic alkanes increase with increasing carbon number. The optical properties of complex cycloalkanes do not vary predictably with increasing carbon number but instead depend on variations in the hydrocarbon structure in addition to hydrocarbon size. An understanding of the fundamental optical properties of this class of compounds is directly applicable to the identification of a high index and low-absorbance fluid for 193 nm immersion lithography.

Molecular dynamics simulations of near-surface modification of polystyrene: Bombardment with Ar+ and Ar+/radical chemistries

Molecular dynamics (MD) simulations have been carried out to examine the effects of Ar+, Ar+/H, and Ar+/F bombardment of a model polystyrene (PS) surface. For bombardment with 100 eV Ar+ only, the simulations show the formation of a heavily cross-linked dehydrogenated damaged layer in the near-surface region after some initial fluence, consistent with plasma and beam system experimental results. The 1–2 nm thick amorphous carbon-rich modified layer has a much lower sputter yield compared to that of the virgin PS, which has a H:C ratio of 1. Simultaneous bombardment of the damaged dehydrogenated PS layer with 300 K H or F radicals and 100 eV Ar+ can facilitate the removal of the layer as well as inhibit its initial formation. The development of the steady-state dehydrogenated layer under Ar+-only bombardment results from a competition between the breaking of carbon-hydrogen bonds (which leads to dehydrogenation and subsequent cross-linking) and the breaking of carbon-carbon bonds (which leads to sputtering...

Redox-Active Ligands: An Advanced Tool To Modulate Polyethylene Microstructure.

The ability to control catalytic activity and selectivity via in situ changes in catalyst oxidation-state represents an intriguing tool for enhanced polymerization control. Herein, we report foundational evidence that catalysts bearing redox-active moieties may be used to synthesize high molecular weight polyethylene with tailored microstructure. The ability to modulate branching density and identity is facilitated by ligand-based redox chemistry, and is realized via the addition of chemical reductants into the polymerization reactor. Detailed GPC and NMR analyses demonstrate that branching density may be altered by up to ∼ 30% as a function of in situ added reductant.