We compared dressed-photon-phonon (DPP) etching to conventional photochemical etching and, using a numerical analysis of\ntopographic images of the resultant etched polymethyl methacrylate (PMMA) substrate, we determined that the DPP etching\nresulted in the selective etching of smaller scale structures in comparison with the conventional photochemical etching. We\ninvestigated the wavelength dependence of the PMMA substrate etching using an O2 gas. As the dissociation energy of O2 is\n5.12 eV, we applied a continuous-wave (CW) He-Cd laser (? = 325 nm, 3.81 eV) for the DPP etching and a 5th-harmonic Nd:YAG\nlaser (? = 213 nm, 5.82 eV) for the conventional photochemical etching. From the obtained atomic force microscope images, we\nconfirmed a reduction in surface roughness, R\na, in both cases. However, based on calculations involving the standard deviation of\nthe height difference function, we confirmed that the conventional photochemical etchingmethod etched the larger scale structures\nonly, while the DPP etching process selectively etched the smaller scale features
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