High-aspect-ratio microfabrication of crosslinked polytetrafluoroethylene using synchrotron radiation direct photo-etching

High-aspect ratio micro-fabrication of crosslinked polytetrafluoroethylene (PTFE) has been carried out using synchrotron radiation (SR) direct photo-etching. The etching rates of crosslinked PTFE samples with various crosslinked densities were studied by changing photon fluence of SR at different sample temperatures. The maximum etching rate of 150 micron/min was achieved at SR beam current of 600 mA. The etching rate of the sample with higher crosslinking density resulted in a higher etching rate. This rate was about two times higher than that of non-crosslinked PTFE. The effects of molecular motion and fragmentation of the molecules on etching process were discussed from temperature dependence on etching rate. Furthermore, we have found that surface modification of non-crosslinked PTFE had been proceeding during irradiation of SR to the surfaces at 140 °C. The modified surfaces were examined on behavior of crystallites by differential scanning calorimetry, and on chemical structure by FTIR spectroscopy and solid-state F NMR spectroscopy. The results showed that properties of modified layers have dependence on depth. Crosslinking reaction would be induced by SR irradiation even in its solid state within about 50 μm from the surface.