Photokinetic etching of polymethyl methacrylate films by continuous wave ultraviolet laser radiation

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Abstract
Continuous wave laser radiation from an argon-ion laser in the wavelength range 300–330 nm or 350–380 nm can be used to etch doped polymethyl methacrylate (PMMA) films with as little thermal damage as from a pulsed, ultraviolet laser (308 or 351 nm) provided the laser spot is moved over the surface at speeds at which the transit time over its own diameter is in the order of 1–200 μs. The laser beam is focused to a spot so that its power density at the polymer surface is between 10 and 100 kW/cm2. There is an optimum speed at a given power density and wavelength at which the cutting action is a maximum. The material that is removed is vaporized in part and the rest collects in and around the cut channel as a low melting polymer. There is no acoustic report similar to that seen in ablative photodecomposition. The process is quite similar to the photokinetic etching that has been described in polyimide films using cw ultraviolet laser radiation. The mechanism of the process can be a thermal depolymerization of the PMMA that is brought about by the photon energy.