AMBIENT GAS EFFECTS ON DEBRIS FORMED DURING KRF LASER ABLATION OF POLYIMIDE

The surface debris that results from KrF excimer laser ablation of polyimide has been investigated as a function of the pressure, and atomic or molecular weight of several ambient gases: H-2, He, Ne, air, Ar, Kr, and Xe. A linear relation between the measured debris radius and the inverse third root of the ambient pressure was found to exist, consistent with the predictions of blast wave theory. No measurable debris could be observed using helium or hydrogen gases up to 1 atm, similar to previous reports on helium. The derived value of the blast energy, equal to about 5% of the incident pulse energy, was used to estimate a nascent blast pressure of approximately 150 atm. By making the assumption that surface debris will form if the ablation fragments are confined in a "small" volume for a "sufficient" time, conclusions from blast wave theory suggest how to decrease the amount of generated debris.