Ablation of inorganic materials using laser plasma soft X-rays

Abstract

We have investigated ablation of inorganic materials using pulsed and focused soft X-rays. Soft X-rays in a range of 1-500 eV were produced by irradiation of Ta targets with Q-switched Nd:YAG laser light (532 nm, 0.5-0.8 J/pulse) with a pulse duration of 10 ns in a vacuum chamber. The soft X-rays were focused on the surfaces of inorganic materials using an ellipsoidal mirror at approximately 0.1 J/cm². The ellipsoidal mirror is designed so as to focus soft X-rays at about 100 eV efficiently, while it can not reflect soft X-rays above 200 eV. We found that synthetic quartz glass, Pyrex, LiF, CaF₂, Al₂O₃ and LiNbO₃, can be ablated by focused and pulsed soft X-rays. Typically, synthetic quartz glass is ablated at 50 nm/shot. We found that ablation occurs at X-ray fluences beyond the ablation threshold. Using a nano-scaled contact mask, trenches with a width of 50 nm and an aspect ratio of 1 are formed. The result indicates the diffusion length of absorbed energy during irradiation is less than 50 nm and that the accumulation results in ablation. The technique can also be applied to basic research of the interaction of intense soft X-rays with materials and resulting damage to the materials.