Experiments that demonstrate quantitatively the importance of laser absorption dynamics for ultraviolet laser ablation of organic materials are presented. Laser pulse transmission measurements have been performed on 0.1 μm spin-coated polyimide films at three ultraviolet wavelengths (193 nm, 248 nm, and 355 nm) over the fluence range 10-3 -10 J/cm2. Target transmission is observed to increase with increasing fluence by a factor of ∼5 at 193 nm, and a factor of ∼10 at 248 nm. In contrast, transmission decreases by approximately one half during 355 nm target irradiation. These results are analyzed theoretically with a two-level model of chromophore absorption. This theory is also applied to reported pulsed UV-laser polyimide ablation data. It is shown that an accurate description of the fluence-dependent film absorption leads to a prediction of the etch depth versus pulse fluence relationship in good agreement with experimental data.
ASJC Scopus subject areas
- Materials Science(all)
- Physics and Astronomy (miscellaneous)