The copolymerization of ethene with norbornene derivatives, as well as their terpolymerization with 1-alkenes, using a series of neutral, square-planar nickel complexes containing anionic P∼O chelates is described. In copolymerizations, up to 50 mol % incorporation of norbornene, leading to an essentially alternating copolymer, is obtained. With norbornene derivatives bearing oxygen functionalities, the level of incorporation is lower, as are the reaction rates and polymer molecular weights. In the case of terpolymerization of ethene and norbornene with 1-alkenes, the polymer molecular weights tend to be low because of slower monomer insertion and additional chain-transfer pathways that are available following 1-alkene insertion. For the ethene/norbornene polymers synthesized, the glass transition temperature (T g) increases smoothly with increasing norbornene content. Solution-cast films of the polymers show good optical clarity.

A processing method has been demonstrated for the fabrication of microchannels using photosensitive polynorbornene copolymer based sacrificial materials. The channel geometric patterns of sacrificial polymer were made via photolithography. The sacrificial polymer patterns were encapsulated with a dielectric medium and then thermally decomposed to form air channels. For the thermal decomposition of sacrificial polymer, the heating program was determined on the basis of the kinetic model obtained from thermogravimetric analysis to maintain the decomposition at a constant rate. The results indicate that a properly selected heating program can avoid the deformation in the channel structure; at the same conditions, a large-size channel is more easily deformed than a small one. The tapered-structure microchannels were also produced using a gray-scale mask. The result shows that a suitably low contrast for the photosensitive sacrificial material can lead to smooth and tapered microchannels.

The effect of epoxy-based cross-linking additives with different functionalities on the photolithographic properties, adhesion to substrates, and cross-link density of a tetramethyl ammonium hydroxide-developable polynorbornene-based dielectric was investigated. Three different multifunctional epoxy additives were investigated: difunctional, trifunctional, and tetrafunctional compounds. It was found that incorporation of a small quantity (1 wt % of solution) of an ultravioletabsorbing tetrafunctional cross-linker, tetraphenylol ethane tetraglycidyl ether, activated the photo-catalyst and improved the sensitivity of a previously photosensitive polynorbornene-based formulation by a factor of 3.7. The impact of the epoxy cross-linkers on the physical and optical properties of the polymer formulations was evaluated. The contrast was improved from 7.37, for the control formulation, to 24.2. The polymer-to-substrate adhesion was also improved by addition of the tetrafunctional epoxy cross-linker, which facilitates the development of high-aspect-ratio structures. Hollow-core pillar structures in 40-lm-thick films with a depth-towidth aspect ratio of 13 : 1 were produced. The cross-link density was studied by using swelling measurements of cured films to evaluate the average molecular weight between cross-links.

Previously, a novel method for fabricating microfluidic and microelectromechanical devices with buried microchannel structures using thermally sacrificial polymers was reported. These previous methods required separate lithographic and etching sequences to pattern the sacrificial polymer. In this work, a more advanced approach in which the sacrificial material is radiation sensitive and can be patterned directly using standard lithographic techniques is explored. The lithographic performance of a new class of photosensitive polynorbornene ͑PNB͒ sacrificial materials has been characterized. The effect of soft bake and postexposure bake ͑PEB͒ on the cross-linking of photodefinable PNB has also been investigated. It was found that significant cross-linking of PNB occurs after exposure during the subsequent postexposure bake. However, this phenomenon is strongly dependent on the soft bake conditions used in preparing the sample, presumably due to varying levels of residual solvent content. This may be due to the high mass transport of the reactive species because of evaporation of residual solvent and shrinking of polymer matrix during the PEB process. No noticeable influence of residual solvent on cross-linking has been found during exposure.

Low dielectric constant materials are critical to meeting the demand for continual reduction in feature sizes and increase in interconnect density required for future high-speed microelectronic devices. Polymers based on functionalized norbornenes are inherently attractive for these applications as they exhibit good electrical properties such as a low dielectric constant and appealing mechanical properties. Although polynorbornenes inherently possess properties that are attractive for microelectronics packaging, films of these polymers are not solvent-resistant. Solventresistant crosslinked films can be attained by generation of acid species to promote cationic crosslinking of epoxide side groups. This article is the second part of a two-part study investigating the crosslinking of a copolymer of decyl norbornene and epoxide norbornene. In the first part of this study, it was proposed that epoxide decomposition reactions are also possible at cure temperatures greater than 160°C. This decomposition mechanism results in the complete loss of crosslinkable epoxide groups while leaving the norbornene backbone intact. Although crosslinking and decomposition reactions have independent mechanisms, both reactions directly affect the level of crosslinking. In this part of the study, the solvent swelling behavior, tensile modulus, elongation to break, and residual stress were investigated for polymer films cured under various conditions to validate the proposed mechanisms. The trends observed with these properties are consistent with the counteracting nature of epoxide crosslinking and decomposition reactions.