Laser ablation of polymers in pressurized gas ambients

Abstract

Excimer-laser ablation of polyimide films into He and N₂ atmospheres in the pressure range of 5×10⁻⁵–10⁻² atm is reported. Using 193 nm radiation at 1 J/cm², it was found that the etch depth per pulse decreases by a factor of 2 with increasing ambient pressure. A description of the ablation process is presented in terms of a strong point explosion model with an outgoing shock wave which produces ingoing drag forces in the gas near the film. These drag a fraction of the ablated fragments and partially redeposit them onto the sample, thus reducing the observed etch depth per pulse.