Excimer laser ablation of polyimide-doped poly(tetrafluoroethylene) at 248 and 308 nm

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Abstract
Experimental data on the 248 and 308 nm wavelength excimer laser ablation at poly(tetrafluoroethylene) doped with polymide (PI) are reported for a range of fluences and dopant concentrations. Threshold fluences were determined and a correlation was obtained between the dopant concentration and the threshold fluence. The threshold fluences and the limiting etch rates at high fluences decreased with increasing dopant concentration, and there is a minimum dopant concentration below which there is no ablation at both of the wavelengths. The side wall taper of the ablated holes increased with increasing dopant concentration. At subthreshold fluences, the polymer surface was modified with selective removal of PI from the polymer blend. The etch rates have been modeled using a two parameter thermal model to describe the etching process. The parameters obtained by fitting the data are qualitatively correlated to the dopant concentration and the measured limiting etch rates.