The properties of a new aqueous-base-develop, negative-tone photosensitive polynorbornene have been characterized. High-aspect-ratio features of 7:1 (height:width) were produced in 70-lm-thick films in a single coat with straight side-wall profiles and high fidelity. The polymer films studied had contrast of 12.2 and low absorption coefficient. To evaluate the polymerÕs suitability to microelectronics applications, epoxy crosslinking reactions were studied as a function of processing condition through Fourier-transform infrared spectroscopy, nanoindentation, and dielectric measurements. The fully crosslinked films had an elastic modulus of 2.9 GPa and hardness of 0.18 GPa.

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.

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