Structure property relations of photoreactive polymers designed for laser ablation

The ablation characteristics of various polymers were studied at low fluenc es, and structure property relations were obtained. The polymers containing the photochemically most active group (triazene) are also the polymers wit h the lowest threshold of ablation and the highest etch rates, followed by a designed polyester and then polyimide. No pronounced influences of the ab sorption coefficients, neither alpha (lin) nor alpha (eff), on the ablation characteristics are detected. The thermal properties of the designed polym ers are only of minor importance. Intensities of fragments obtained by time -of-flight mass spectrometry measurements show pronounced differences betwe en irradiation at the absorption band of the triazene group (308 nm) and ir radiation at a shorter wavelength (248 nm). The larger fragments reveal low er intensities for 248 nm irradiation, due to the additional decomposition of these fragments by the higher energy of 248 mn photons and the lower etc h rates for 248 mn irradiation. An excimer lamp emitting at 308 nm is appli ed to decompose the triazene group without major decomposition of the aroma tic system. Irradiation with shorter wavelengths, i.e. 222 and 172 nm, caus es in addition the decomposition of the aromatic system. Two novel applicat ions for the special designed photopolymers are shown. These polymers can b e applied in combination with phase masks for the fabrication of microoptic al elements using laser ablation. Another quite different application utili zes near-IR irradiation. The plasma created by laser ablation acts as a mic ro thruster. (C) 2001 Elsevier Science B.V. All rights reserved.