Ablation plume particle dynamics during excimer laser ablation of polyimide

The dynamics of polyimide ablation plume particles generated during ArF excimer laser (193 nm) ablation were investigated using time-resolved, laser light scattering and Raman spectroscopy. The evolution of plume particle size is determined over a range of 300-1150 μm above the polymer target surface. Raman-scattering measurements of the ablation plume allow in situ identification of the particle composition, which is equivalent to flame generated soot. The total mass of particulate carbon within the plume accounts for approximately 1% of the total carbon mass within the ablated polyimide. Scanning electron microscopy was used to examine the size and morphology of collected plume particles, which were found to correlate remarkably with the light-scattering results. The formation of particulate carbon within the ablation plume is apparently complete within 500 μm above the polymer surface, corresponding to a time scale of 30 μs, and then gives way to carbon oxidation at greater heights. It is concluded that particulate carbon is formed within the resulting ablation plume, with subsequent particle growth and oxidation processes being important in the evolution of the particles.