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.

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.

ABSTRACT:The exposure characteristics of norbornenebased photosensitive sacrificial materials as functions of the photoinitiator have been investigated. The results show that the initiator, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, provides high photosensitivity and an adjustable contrast factor. The kinetics of the thermal decomposition of the polymers have been investigated with dynamic and isothermal thermogravimetric analysis to determine the most appropriate conditions for the thermal decomposition of the sacrificial polymers. The reaction is slightly higher than first-order, and a single mechanism can account for the decomposition throughout the process. The dependence of the kinetic parameters on the composition of the copolymers has been studied, and the reaction order remains unchanged; however, the activation energy is lower when the alkenyl-substituted norbornene content is increased in the copolymers.