Investigation of Denaturation of Hydrophobic Perfluoropolymer Surfaces and Their Applications for Micropatterns on Biochip

The mechanism causing the denaturation of hydrophobicity of a micropatterned perfluoropolymer surface through the damage that occurs during the fabrication process is investigated. Using the results of the investigation, we successfully formed highly hydrophobic patterns without any loss of hydrophobicity even on low-thermal-tolerance substrates such as polycarbonates. We previously reported that the loss of hydrophobicity could be reduced by employing Cu as a dry etching mask and that hydrophobicity could be restored by postannealing the surface at 230°C. In this study, we investigate the detailed influence of process parameters on the binding condition and hydrophobicity of the perfluoropolymer surface. Even when the postannealing temperature was reduced to 145°C , by employing 50-nm-thick Cu as an etching mask, it was possible to form highly hydrophobic perfluoropolymer patterns having a contact angle of 110.3°. The hydrophobicity of the formed surface could be restored to its original value by postannealing at 145°C. This was possible because the depth of the damaged perfluoropolymer surface that contained unsaturated bonds was shallower when a Cu mask was used than when an Al mask was used. The developed technology can be employed in biochip applications such as cell patterning and droplet generation.