Excimer laser etching of polyimide

TLDR

The study used IR spectroscopy and GC/MS to detect gases released during polyimide laser etching in air and vacuum. Thin polyimide films are efficiently etched by pulsed excimer lasers at 248–351 nm, with etch rates following a Beer–Lambert relation and fluence thresholds linked to absorption, indicating a predominantly thermal mechanism independent of wavelength.

Abstract

It is reported that thin films of polyimide are efficiently etched in air at pulsed excimer laser wavelengths of 248, 308, and 351 nm. Etch rate versus incident fluence data are found to obey a Beer–Lambert etching relation. Sharp laser fluence thresholds for significant etching are found to correlate with the wavelength-dependent absorption coefficient. The absorbed energy density required to initiate significant etching is found, within experimental error, to be independent of the wavelengths examined. It is felt that this information demonstrates the predominantly thermal nature of the laser etching mechanism. Additionally, infrared spectroscopy and coupled gas chromatography/mass spectroscopy were used to identify several gases evolved during pulsed laser etching of polyimide in both air and vacuum.