SELECTIVE FEMTOSECOND LASER STRUCTURING OF A PLATINUM/TANTALUM PENTOXIDE THIN FILM LAYER SYSTEM BY INDUCED LASER ABLATION INVESTIGATED WITH PUMP-PROBE MICROSCOPY

摘要

A biocompatible sensor chip consists of a 200 nm conducting platinum layer between a glass substrate and a 200 nm tantalum pentoxide layer as insulator on top. The irradiation of the biochip from the Ta_2O_5 side with ultra-short laser pulses (660 fs) at a wavelength of 1053 nm leads to a selective ablation of the Ta_2O_5 layer from the platinum. The ablation threshold for the removal of the Ta_2O_5 layer is about 0.08 J/cm~2. Moreover, the Ta_2O_5 lifts-off in form of an intact disk at a fluence of 0.14 J/cm~2. For deeper understanding of the ablation mechanisms, a pump-probe microscopy setup was utilized to record a stop-motion movie of the lift-off process. The setup utilizes an optically combined with an electronically delayed probe pulse. For the first time to our knowledge the laser lift-off of a transparent oxide could be recorded over the complete temporal dynamic range. The movies reveal that an intact disk leaves the hole after a few 10 ns. At higher fluences of about 0.20 J/cm~2 the disk disrupts in several particles at about 40 ns.