Surface enhanced Raman spectroscopy for non-destructive analysis of surfaces following excimer laser removal of polyimide

In this study, surface enhanced Raman spectroscopy (SERS) has been investigated as a nondestructive technique for monitoring the cleanliness of gold surfaces following KrF excimer laser removal of ∼2 μm-thick polyimide films. 1360 cm^-1 (D line) and 1580 cm^-1 (G line) carbon sensitive bands were detected in the Raman spectra of samples cleaned with up to 100 laser pulses at fluences in the range 120-140 mJ/cm². The Raman intensity ratio I_D/I_G increased with the number of pulses, indicating that graphite-like carbon residues were being broken down into smaller fragments with prolonged exposure. The same two carbon peaks disappeared from the Raman spectra of samples subjected to further cleaning, indicating complete removal of carbon residues from the surface. The results show that SERS is a useful in-situ, non-destructive technique for monitoring polyimide laser ablation and cleaning processes.