Mass Spectral Identification of UV-Laser Photoablation Products from Polymers

Abstract

Recently, much attention has been given to the laser photoablation of polymeric films because of applications to the etching processes involved in the microelectronics industry. For a number of compounds, including PMMA ( polymethylmethacrylate), PET (poly (ethylene terephthalate)), polycarbonate, and polyimide, it has been observed1 that short wavelength (193 nm) laser ablation results in precise and clean etching, while long wavelength (≥248 nm) ablation can result in melting, charring and burning. It has been proposed that the differences cited above in the ablative photodecomposition (APD) are a manifestation of the variation of photochemical quantum yields with wavelength, or possibly with intensity. If the quantum yield(s) for various photolytic processes are in fact wavelength dependent, one would expect that dependence to be manifest as a change in the distribution of volatilized products. We report here the direct observation of such quantum yield variations via mass spectrometric studies of the photoablation products.