REPETITION RATE EFFECT ON THE LASER-ABLATION OF POLYMER STRUCTURES

Multilayer polyimide structures may be used as an etch stop mechanism in laser ablation processing. By changing the optical properties of th e polymer it is possible to better control the depth of the patterns p roduced by the lasers. We present the effect of the repetition rate in the ablation of multilayer structures. The results are obtained from a photothermal model that includes the light absorption by the decompo sed fragments, which shield the polymer from the incoming laser beam. The model also includes an intermediate zone in which the polymer suff ers a phase transition. The evolution of the temperature profiles is s imulated during each pulse taking into account the pulse shape; howeve r, a simple diffusion model is used between pulses. The results of the simulations indicate the range of values for which the multilayer str ucture may be used as an effective etch stop mechanism. We found that the effectiveness of the multilayer structure deteriorates for increas ing repetition rates. (C) 1995 American Institute of Physics.