The emerging technology of excimer laser processing in polymeric, ceramic, metallic, and high Tc materials is of growing interest to the microelectronics and computer industry. Since the first observation of efficient and clean material removal in the early 1980s, using strongly absorbing materials like polyimide, there has been a parallel interest in low dielectric, very weakly absorbing polymeric systems such as PTFE. Since the absorption coefficients of these different materials range from above 106 cm−1 to below 102 cm−1, one observes concomitantly large differences in the fluences necessary to remove material efficiently in these different systems. The initial reports of the suspected mechanism of excimer laser ablation assumed that large absorption cross sections leads to selective bond breakage and relatively low temperatures at the surface of the polymer. This would then explain the clean, damage free features observed in the early patterning efforts. The near threshold spectroscopic measurements that were done on several diatomic species, produced from 308 nm ablation of polyimide, showed that these species displayed relatively low rotational temperatures (<1000 K), which lead to the conclusion that a photochemical process may dominate the early stages of the bond breakage and the eventual removal of macroscopic amounts of material.
© 1991 Optical Society of AmericaPDF Article