Structure property relations of photoreactive polymers designed for laser ablation

The ablation characteristics of various polymers were studied at low fluences, and structure property relations were obtained. The polymers containing the photochemically most active group (triazene) are also the polymers with the lowest threshold of ablation and the highest etch rates, followed by a designed polyester and then polyimide. No pronounced influences of the absorption coefficients, neither alpha (lin) nor alpha (eff), on the ablation characteristics are detected. The thermal properties of the designed polymers are only of minor importance. Intensities of fragments obtained by time-of-flight mass spectrometry measurements show pronounced differences between irradiation at the absorption band of the triazene group (308 nm) and irradiation at a shorter wavelength (248 nm). The larger fragments reveal lower intensities for 248 nm irradiation, due to the additional decomposition of these fragments by the higher energy of 248 mn photons and the lower etch rates for 248 mn irradiation. An excimer lamp emitting at 308 nm is applied to decompose the triazene group without major decomposition of the aromatic system. Irradiation with shorter wavelengths, i.e. 222 and 172 nm, causes in addition the decomposition of the aromatic system. Two novel applications for the special designed photopolymers are shown. These polymers can be applied in combination with phase masks for the fabrication of microoptical elements using laser ablation. Another quite different application utilizes near-IR irradiation. The plasma created by laser ablation acts as a micro thruster. (C) 2001 Elsevier Science B.V. All rights reserved.