Etching polymer films with ultraviolet laser pulses of long (10–400 μs) duration

Abstract

Continuous wave ultraviolet laser radiation (300–330 nm) from an argon ion laser was chopped mechanically with a rotating disk containing an aperture to yield pulses of ∼10–400 μs duration. Such pulses when focused to give spots of radiation of 10–100 kW/cm2 of power density etched films of polymers such as polyimide (KaptonTM), polyethylene terephthalate, and polymethyl methacrylate doped with Tinuvin. This etching process shows several features that are significantly different from the etching of the same materials by 5–35 ns pulses of 308 nm radiation from an excimer laser. These differences are in the fluence threshold for etching, the evidence (or lack thereof) for ablation of the products, and the nature of the etched surface. The etched holes show that there is considerable involvement of a heating effect in this process, but lateral thermal damage outside of the irradiated area is insignificant. The characteristics of this process seem analogous to those seen in photokinetic etching, which uses a moving spot of cw ultraviolet laser light to cut polymer surfaces in transit times of the same order as the durations of the pulses used here.