Optimization of particle fluence in micromachining of CR-39

Polyallyl diglycol carbonate (CR-39 etched track detector) material was irradiated with various doses of 2 MeV protons and alpha-particles in order to optimize the fluence for P-beam writing of CR-39. Irradiation were performed at the Institute of Nuclear Research, Debrecen, Hungary and at the National University of Singapore. Post irradiation work has been carried out in Debrecen. The fluence in the irradiated area was sufficiently high that the latent tracks overlapped and the region could be removed collectively by short etching times of the order of less than 1 min. Theoretical calculations based on analytical and Monte Carlo simulations were done in order to calculate the probability of multiple latent track overlap. Optimal particle fluence was found by minimising the fluence and etching time at which collective removal of latent tracks could be observed. Short etching time is required to obtain high resolution microstructures, while low particle fluence is desirable for economical reasons, and also because high fluences increase the risk of unwanted damage (e.g. melting).