Ultraviolet Laser Photoablation of Polymers: A Review and Recent Results

Abstract

The evolution since 1982, of far-UV laser photoablation of polymers is described. The experimental data can be fitted by using a dynamic model which states that the irradiated interface moves at a rate proportional to the difference between, the intensity reaching it, and the ablation threshold intensity It. The screening effect of the ablated gaseous products is taken into account. The experimental etch depth versus fluence, obtained with our new quartz crystal microbalance technique, can be fitted by adjusting two parameters of this model; the mean absorption coefficient of the products β and the so-called ablation rate constant k, which is the etch rate for I=It+1 MW/cm2. These two parameters are wavelength dependent. The model allows also the calculation of the dose of absorbed energy as a function of depth in the material. For each layer of the ablated depth, the dose absorbed before and after (reabsorption of the gas products) ablation are distinguished. The dose of reexcitation varies highly with fluence and the distribution of gas products broadens accordingly. However, primary products need to be studied. Surface products are formbd on the final surface, during the postablation phase of the pulsed irradiation. The probable mechanism of the evolution of excitation energy is discussed, with stress on the elementary steps leading to heat production.The perspectives of evolution of etching and patterning polymer surfaces by far-UV photoablation are high in basic research and technology.