The effects of feedback control parameters on the formation of protuberances in poly(methyl methacrylate) by dynamic plowing lithography

In this study, nanoscale protuberances were fabricated on poly(methyl methacrylate) (PMMA) thin-film surface by mechanical scanning probe lithography, namely dynamic plowing lithography (DPL). However, the formation mechanism of protuberances by DPL remains unclear. Therefore, this paper investigated the formation mechanism and fine control of the protuberances. Considering the influence of the dynamic response of the probe cantilever, proportional gain and integral gain were investigated when the tip scratched PMMA film in scan mode. Using feedback loop control, the increased depth of the groove at the beginning was attributed to the peak of the oscillation amplitude caused by the interplay between lithography and feedback. The cantilever vibrated dramatically when integral gain was increased. When the integral gain was increased to 5, the machined depth was approximately 82 nm, which exposed the substrate. Furthermore, the machined depth depended on the proportional gain when the integral gain was 0. The increased steady-state error that occurred at decreased proportional gain caused the tip to penetrate the sample deeper. In addition, the volume of the pile-up was larger than the removed material. And the material pile-up contributed to the fabrication of the protuberance. Finally, uniform and reliable protuberances were fabricated without proportional gain and integral gain.