Browsing by Subject "Photopolymerization"

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Design, synthesis and testing of materials for 157 nm photolithography
(2005) Chambers, Charles Ray; Willson, C. G. (C. Grant), 1939-
The microelectronics industries’ ability to keep pace with Moore’s law (the doubling of the number of transistors per integrated circuit every 18 to 24 months) has been due to advances in the photolithographic process. Shrinking the feature sizes that can be printed has been accomplished by decreasing the exposure wavelength which allows higher resolution and thereby more transistors per area. Currently i-line (365 nm) and deep UV (248 nm) are the most frequently used wavelengths for integrated circuit manufacturing. As device geometries shrink below 100 nm, the lithography for critical layers will be performed at an exposure wavelength of 193 nm. The 193 nm technology is being implemented now. Some “next generation” photolithography will be used to print features down to 45 nm. The technology that has investigated the most for printing the 45 nm node is uses 157 nm as the exposure wavelength. As the move is made from one exposure wavelength to the next new photoresist materials are required that have a low absorbance at the lower wavelength. Finding materials for 157 nm photolithography was particularly challenging due to the inherently high absorbance of most materials at this short wavelength. It was discovered that the addition of fluorine into organic molecules greatly increased their transparency at 157 nm. Fluorine or other transparency enhancing moieties were therefore incorporated into analogues of the 193 nm photoresist polymers. New fluoro polymers were prepared by free radical copolymerizations of electron deficient olefins with fluorinated and nonfluorinated norbornenes. Unfortunately the transparency requirements were not fully achieved with the 193 nm photoresist polymer analogues. Highly transparent fluorinated norbornene polymers were prepared using metal catalysts. One such polymer is poly(2-(3,3,3-trifluoro-2-trifuoromethyl-2- hydroxypropyl)bicyclo[2.2.1]hept-5-ene) (PNBHFA). It was discovered that PNBHFA has unique dissolution inhibition properties which are reminiscent of the novolac resin used in two component, non-chemically amplified photoresist system used at 365 nm. A more transparent fluoropolymer (Asahi RS001 polymer) was later introduced. Transparent, highly functionalized additives that could be blended with PNBHFA or the Asahi polymer and used to print high resolution, high aspect ratio images at 157 nm were designed, synthesized and tested.
Investigating the influence of thermal and mechanical properties of resin on the sedimentation rate of the printed geometry in the volumetric additive manufacturing technique
(2022) Salajeghe, Roozbeh; Kruse, Carl Sander; Meile, Daniel Helmuth; Marla, Deepak; Spangenberg, Jon
y layer, volumetric additive manufacturing produces the whole geometry at the same time. While it is faster, creates features with high surface quality, requires no overhang support structures, and can print in high-viscosity resins, all of which push the limits of additive manufacturing, this technique is still premature and suffers from some effects such as body sedimentation that impacts the geometric fidelity and resolution of the final product. The sedimentation rate of the printed body during its formation is highly dependent on the resin type, its viscosity, and its curing behavior. Herein, we propose a CFD model that takes into account the synergistic effect of reaction-based heating, curing behavior, and resin properties to predict the sedimentation rate of the printed geometry. The results show that heating effects can slow down the sedimentation rate of the curing part significantly.
Novel pH-responsive microgels and nanogels as intelligent polymer therapeutics
(2008-08) Fisher, Omar Zaire, 1979-; Peppas, Nicholas A., 1948-
Disease processes that are currently among the leading causes of death now require much more than just a stethoscope for diagnosis and a pill for treatment. The next generation of therapeutics needs to possess a degree of intelligence; the ability to sense and respond to their environment. Biomedical hydrogels have the ability to sense and respond to external stimulus and with the advent of nanotechnology; these polymers can be fabricated on the same size scale as cellular and sub-cellular processes. Throughout the body gradients in pH are used at the cellular level to regulate processes such nutrient transport and to fight infection. Sites of damage or disease within the body are associated with both a change in pH and abnormal nanoporous vasculature. pH-Responsive microgels and nanogels are small enough to access these locations within the body, sense the change in environment, and locally release a therapeutic agent In this work heterogeneous, photoinitiated free radical polymerizations were developed to synthesize novel pH-responsive microgels and nanogels that could be loaded with macromolecular therapeutics and could respond to either a basic or acidic change in pH. A novel photo-dispersion polymerization scheme was developed to synthesize poly(ethylene glycol) grafted poly(methacrylic acid) (P(MAA-g-PEG)) polycomplexation gels for oral protein delivery. These ranged in size from 100- 300 nm in diameter and could swell up to a 17-fold increase in volume, in response to a rise in pH. This property allowed them to protect insulin at low pH and release the protein at neutral pH. In this way the carriers could be used to transport proteins through the stomach to the small intestine for absorption. A novel photo-emulsion polymerization scheme was developed to synthesize poly(ethylene glycol) grafted poly[2-(diethylamino)ethyl methacrylate] nanogels, between 70-150 nm in diameter. These could swell up to a 22-fold increase in volume, in response to a drop in pH. These nanostructures were able to successfully target clathrin-dependent endocytosis and deliver macromolecules to the cytosol.
A Simple Polymer Shrinkage Model Applied to Stereolithography
(1994) Flach, Lawrance; Chartoff, Richard P.
A simple polymer shrinkage model has been successfully applied to the stereolithography process. The shrinkage model, which computes specific volume changes from the degree of conversion of monomer to polymer, incorporates a lag between conversion and shrinkage. An overall process model used to simulate the stereolithography process was modified by inclusion of the shrinkage model. Use of the modified stereolithography process model allows prediction of the shrinkage that might be expected to occur when fabricating a strand of plastic. By varying the lag between conversion and shrinkage it is shown that faster shrinking resins should exhibit lower overall shrinkage than slower shrinking resins. This is a direct result of the fact that less shrinkage occurs after the strand has been scanned for the faster shrinking resins.
Synthesis of organic compounds for two-photon initiated polymerization and molecular recognition
(2003) Postnikova, Brenda Jean; Anslyn, Eric V.
In section I, three-dimensional polymeric objects were fabricated using two-photon initiated polymerization (TPIP) with a two-photon absorbing chromophore and an acrylate resin. The feasibility of fabricating polymeric features on the nanoscale was explored using an enhanced field generated at the apex of a gold tip as the excitation source, as used in near-field excitation (NFE). In section II, C3-symmetric chiral receptors were used to direct enantioselective enolate alkylation. A series of host compounds was synthesized and 1:1 host to enolate binding was observed by 1 H NMR titration experiments. A moderate increase in the enantioselectivity of the alkylation of 2-acetylcyclohexanone was observed in the presence of host 2.22. Also in section II, the use of enolate stabilization via charge-pairing was investigated for the reduction of the pKa of 2- acetylcyclopentanone. In the presence of host 3.12, the pKa of 2- acetylcyclopentanone was reduced by 10 pKa units. In comparison with the 2.9 pKa unit shift observed with host 3.11, this result suggests that charge-pairing is more effective in stabilizing enolates in enzyme active sites than traditional hydrogen bonding.