Excimer laser light induced ablation and reactions at polymer surfaces as measured with a quartz-crystal microbalance

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Abstract
We have developed a new technique to measure the etch rate of polymer films under the ablative photodecomposition condition obtained by absorption of the far-UV radiation of the excimer laser. The technique is based on the use of a quartz-crystal microbalance interfaced with a microcomputer. It has high accuracy (17 ng/cm2). Etch rates of poly(ethylene terephthalate), polycarbonate, and polystyrene were measured as a function of the laser intensity, at 193 and 248 nm. The etch rate in the region of the ablation threshold intensity is obtained precisely. A slow ablation regime between the threshold and the linear regime is evidenced. For polycarbonate and polystyrene, a reaction of the irradiated surface with molecular oxygen accelerates the ablation process at low fluence of the 248 nm radiation. The degradation reaction of poly(ethylene therephthalate) is monitored as a function of fluence by selective dissolution in acetone. A sudden increase of the degraded depth is seen at the transition between the two ablation regimes. This is attributed to the melting of the surface.

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