Ultraviolet Laser Photoablation of Polymers: A Review and Recent Results

The evolution since 1982, of far-UV laser photoablation of polymers is described. The experimental datacan be fitted by using a dynamic model which states that the irradiated interface moves at a rateproportional to the difference between, the intensity reaching it, and the ablation threshold intensityI t .The screening effect of the ablated gaseous products is taken into account. The experimental etch depthversus fluence, obtained with our new quartz crystal microbalance technique, can be fitted by adjustingtwo parameters of this model; the mean absorption coefficient of the products β and the so-called ablationrate constant k, which is the etch rate forI=I t + 1 MW/cm 2 . These two parameters are wavelengthdependent. The model allows also the calculation of the dose of absorbed energy as a function of depth inthe material. For each layer of the ablated depth, the dose absorbed before and after (reabsorption of thegas products) ablation are distinguished. The dose of reexcitation varies highly with fluence and thedistribution of gas products broadens accordingly. However, primary products need to be studied. Surfaceproducts are formbd on the final surface, during the postablation phase of the pulsed irradiation. Theprobable mechanism of the evolution of excitation energy is discussed, with stress on the elementary stepsleading to heat production. The perspectives of evolution of etching and patterning polymer surfaces by far-UV photoablation arehigh in basic research and technology.