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

Abstract

Fabrication of curved structures with electron-beam and surface structure characterizationA direct etching phenomenon of polytetrafluoroethylene (PTFE) is reported via 1.0 MeV proton beam writing. With a fluence level of more than 0.9 lC/mm 2 , direct etching of the PTFE is observed using a scanning electron microscope. The decrease of CF 2 and CF 3 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 lC/mm 2 , the depth of the micromachining increases to around 55 lm, which is larger than the predicted range of 16.5 lm 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 lm wide and with a height of 16 lm has been demonstrated. This direct PTFE etching technique may open new possibilities for micromachining PTFE molds by proton beam writing for polydimethylsiloxane replica molding.

The potentialities of ultrasound as an alternative to chemical etching for proton beam writing micropatterning

“…For the present case, the efficient removal of material depends on several factors including the type of polymer, the irradiation parameters and the etching technique adopted as a post-irradiation treatment. For PTFE, previous studies showed that techniques like a thermal treatment carried out after the patterning through PBW 11 and in-air patterning 12 turns rough structures into smooth ones with good aspect ratio. For other polymers such as polyethylene terephthalate (PET, Mylar ® ), an etching procedure consisting of a 6 M NaOH solution in a thermal bath with magnetic stirring has been used successfully for the removal of the damaged structures.…”

“…10 Moreover, Nishikawa and Hozumi showed that a thermal treatment carried out after the patterning of PTFE through PBW turns rough structures into smooth ones with good aspect ratio. 11 Smooth structures have been obtained as well once the PWB process takes place in the presence of an oxygen-rich environment. Therefore, this kind of experiment can be carried out under ambient pressure (in air) with an external beam setup 12 if good aspect ratio structures are needed.…”