F2 excimer laser (157 nm) ablation of polymers: Relation of neutral and ionic fragment detection and absorption

Abstract

The ablation products of various polymers (triazene polymers, polyimides and glycidyl azide polymer) with 157 nm F2 laser irradiation were studied with time-of-flight mass spectroscopy, ion probe and white-light interferometry. In contrast to the ablation with longer UV wavelengths, 157 nm irradiation results in non-preferential bond-breaking and a much more pronounced fragmentation into fragments with masses <50 amu. This result suggests a photochemical ablation process that occurs at any bond in the molecule. In addition, ions have been detected at very low fluence similar to the threshold of neutral detection, which is below 30 mJcm-2 for the triazene polymers and Kapton. The observation of ions from the onset of ablation suggests a 2-photon ablation mechanism and possibly involves an excited neutral as an intermediate step. The low thresholds were verified by ion probe measurements of the ablation plume and white-light interferometry of the ablated target surface. © 2007 IOP Publishing Ltd.