Time and space resolved investigations of confined fs ablation of Ta 2 O 5 /Pt thin film systems

Maskless patterning of biocompatible sensor chips consisting of a Ta 2 O 5 /Pt/glass layer system can be realized by ultrashort laser pulse ablation allowing fast and precise structuring. Here, a 650 fs laser at a center wavelength of 1053 nm is used at a peak fluence of 5 J/cm 2 . It was observed, that a greater diameter of the Pt film (400 nm) is ablated when it’s coated with Ta 2 O 5 (200 nm) compared to the uncoated Pt. One reason was found in the anti-reflective effect of the Ta 2 O 5 layer causing an increase of energy deposition in the material. The underlying physical effects of the ablation reaction are investigated over the whole reaction time ranging temporally from fs to μs by ultrafast pump-probe microscopy. For the direct ablation of the uncoated Pt, results show ultrafast heating and melting after 2 ps, the creation of a gas-liquid mixture and plasma at 10 ps. At around 100 ns the actual ablation takes place indicated by the ejection of small particles. The results for the Ta 2 O 5 /Pt layer system reveal heating and electron excitation in the Ta 2 O 5 layer during the first 2 ps. In the following the spot center behaves identical to the direct ablation of Pt. Here, the Ta 2 O 5 is ablated with the Pt. A confined ablation where an additional amount of laser energy is deposited in the layer system or at the layer interface is assumed to take place. In the rim of the spot only the Ta 2 O 5 is removed by indirectly-induced ablation at around 35 ns.