A photoacid generator (PAG) is described that can be efficiently activated by two-photon excitation and can be used for high-sensitivity three-dimensional micro-patterning of acid-sensitive media. The molecule has been specifically engineered to have both a large peak two-photon absorption cross section (δ = 690 x 10<sup>-50</sup> cm<sup>4</sup> s photon<sup>-1</sup> at 705 nm) and a high quantum yield for the photochemical generation of acid (φ<sub>H</sub>+ ≈ 0.5). Under near-infrared laser irradiation, the PAG produces acid subsequent to two-photon excitation and initiates the polymerization of epoxides. The PAG was used in conjunction with the epoxide resist SU-8 for negative-tone three-dimensional microfabrication and was incorporated into a specially formulated chemically amplified resist for positive-tone fabrication of a three-dimensional grating structure. These material systems expand the potential of three-dimensional microfabrication as a tool for manufacturing micro-electromechanical systems, micro-fluidics, and micro-optical structures.
A new photoacid generator (PAG) is described that can be efficiently activated by two-photon excitation and can be used for high-sensitivity three-dimensional micro-patterning of acid-sensitive media. The molecule has a large two-photon absorption cross section that peaks near 705 nm (<i>δ</i> = 690 x 10<sup>-50</sup> cm<sup>4</sup> s photon<sup>-1</sup>) and a high quantum yield for the photochemical generation of acid (<i>φ</i><sub>H+</sub> ≈ 0.5). Under near-infrared laser irradiation, the molecule produces acid subsequent to two-photon excitation and initiates the polymerization of epoxides at an incident intensity that is one to two orders of magnitude lower than that needed for conventional ultraviolet-sensitive initiators. The new PAG was used in conjunction with the solid epoxide resist Epon SU-8 for negative-tone three-dimensional microfabrication.
Hydrogels have gained general acceptance as biocompatible materials and are the basis of many promising applications in tissue engineering, drug release formulations and biosensors. Polymer processing techniques that can generate miniature hydrogel microstructures are not only critical as scaffolds for tissue re-growth but also very effective for increasing the efficiency of drug delivery and biosensors. Our approach is to use both optical and soft lithographic methods to microfabricate hydrogels. In this paper, we describe a photolithographic process to pattern hydrogel materials and analyze factors influencing sensitivity and lateral resolution. The model system we are investigating is based on 2-hydroxyethyl methacrylate (HEMA), which is well known for its non-toxicity and its widespread use in the contact lens industry.
Plasma (dry) etching is a key step in semiconductor device manufacturing processes whereby the resist pattern is transferred to a substrate. As the resist thickness is reduced to meet stringent transparency requirements in photolithography, the usage of fast etching material as BARC is considered to be increasingly critical in minimizing resist thickness loss in pattern transfer steps. Several models emphasizing correlation between polymeric structure and etch resistance based on empirical parameters have been developed but are hard to generalize. We have examined the reactive ion etch (RIE) properties of a variety of polymer groups including natural polymers, poly(styrenic)s, poly(acrylate)s, poly(olefin)s, poly(ester)s and several polymers grafted with UV light absorbing chromophores. With the assumption that in the etching processes the reactive species from plasma attack the polymeric materials at a molecular level instead of an atomic level, we have developed a model based on the contribution of chemical bonds in the polymer structure to predict etch rates. The present study shows that this model revealed marked correlations across polymer families for three different etch processes. This model has also proved to be an effective tool in predicting the etch behavior of polymers for use in BARCs.