DOPANT-INDUCED EXCIMER LASER ABLATION OF POLY(TETRAFLUOROETHYLENE) .2. EFFECT OF DOPANT CONCENTRATION

Clean ablation of poly(tetrafluoroethylene) (PTFE) at etch rates in excess of 7 mum/pulse has been achieved with an excimer laser using 308 nm radiation and a 25 ns pulse width. This was accomplished by doping the ultraviolet-transparent PTFE polymer with polyimide. Ablation rates were investigated as a function of fluence in the range from 1 to 12 J/cm2 and dopant levels up to 15% (wt/wt). Results show that at a given fluence there exists an optimum absorption coefficient alpha(max), for which maximum ablation rates are achieved. The value of alpha(max) was found to decrease with increasing fluence. The relationship between alpha(max) and fluence was determined from existing ablation rate models and found to compare favorably with empirical results.