Application of proton beam writing for the direct etching of polytetrafluoroethylene for polydimethylsiloxane replica molding

A direct etching phenomenon of polytetrafluoroethylene (PTFE) is reported via 1.0 MeV proton beam writing. With a fluence level of more than 0.9 μC/mm², direct etching of the PTFE is observed using a scanning electron microscope. The decrease of CF₂ and CF₃ bonds in the PTFE composition is also observed using Fourier-transform infrared analysis, which indicates that the decomposition of the PTFE is involved in the direct etching process. With increasing proton beam fluence levels up to 9.6 μC/mm², the depth of the micromachining increases to around 55 μm, which is larger than the predicted range of 16.5 μm for 1.0 MeV protons incident on PTFE. Coupled with heat treatments in vacuum or in air at temperatures of more than 200 °C, holes with smooth sidewalls and a smooth bottom surface are obtained. Polydimethylsiloxane replication of square patterns down to 5 μm wide and with a height of 16 μm has been demonstrated. This direct PTFE etching technique may open new possibilities for micromachining PTFE molds by proton beam writing for polydimethylsiloxane replica molding.