Observation of a Spot Diameter Dependency in Confined Laser Ablation of Zinc Oxide on Copper-Indium-Diselenide

Confined laser ablation with ultra-short laser pulses, also referred to as laser “lift-off”, is initiated at the interface of transparent thin films and underlying absorbing substrates. The energy per ablated volume at confined laser ablation (<10J/mm3) is higher than at direct laser ablation (about 100 J/mm3). In this paper the selective laser structuring of a zinc oxide (ZnO) / copper-indium-diselenid (CIS) layer system is investigated with 10 ps and 460 fs long laser pulses. Spot diameters between 14 μm and 100 μm were selected to show the relation between the spot diameter and the so called punching fluence. This value describes the lowest fluence at which the laser “lift-off” takes place. For both pulse durations the punching fluence depends on the spot diameter. The punching fluence increases from about 0.4 J/cm2 at spot diameters ≥40 μm to about 1.1 J/cm2 for decreasing spot diameters <40 μm.