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

In this paper, we explore the potentialities of using ultrasound waves as a post-irradiation treatment after proton beam writing (PBW) patterning of PTFE. To that end, 2-mm-thick foils of PTFE were irradiated with 2.2 MeV protons with an average current of 50 pA. Straight line structures were patterned on the polymer with a 3.5 × 3.5 μm$^2$ focused proton beam. Post-irradiation polymers were placed in a heat bath at 60 °C and immersed either in distilled water or in a 6 M solution of NaOH under the action of 40 kHz ultrasound waves for developing the patterned structures. The results indicate that distilled water submitted to ultrasound waves is very efficient for removing rough structures created by the proton irradiation and thus providing a good aspect ratio to the PBW microstructures. On the other hand, the use of 6 M NaOH instead of water did not improve the quality of the structures patterned with the proton beam. The results are discussed in terms of the parameters that characterize the interaction of ultrasound waves with the liquid media and the polymer.