Ablation of Submicrometer Holes Using an Extreme-Ultraviolet Laser

Simulations and experiments are used to study extreme-ultraviolet (EUV) laser drilling of submicrometer holes. The ablation process is studied with a 2D Eulerian hydrodynamic code that includes bound-free absorption processes relevant to the interaction of EUV lasers with a solid material. Good agreement is observed between the simulated and measured ablated depths for on-target irradiances of up to 1×1010 W cm-2. An increase in the irradiance to 1×1012 W cm-2 is predicted to ablate material to a depth of 3.8 μm from a single pulse with a hole diameter 3 to 4 times larger than the focal spot size. The model allows for the simulation of the interaction of a laser pulse with the crater created by a previous shot. Multiple-pulse lower-fluence irradiation configurations under optimized focusing conditions, i.e., approaching the diffraction limit, are shown to be advantageous for applications requiring mesoscale [(100 nm)-(1 μm)] features and a high level of control over the ablation profile.