Nano-ablation of inorganic materials using laser plasma soft X-rays at around 10 nm

We have investigated direct nanomachining of inorganic materials using laser plasma soft X-rays. Soft X-rays (X) were generated by irradiation of Ta targets (Ta) with 532 nm Nd:YAG laser light(Y) with a pulse duration of 7 ns, at an energy density of about 10⁴ J/cm². Under the condition, Ta plasma emit soft X-rays at around 10 nm. The soft X-rays were focused on samples (Q) with a spot size of 150 μm, using an ellipsoidal mirror (M) that we designed so as to focus soft X-rays at around 10 nm efficiently. It was confirmed that SiO₂ has optical absorption at around 10 nm. We found that synthetic quartz glass, fused silica, Pyrex, HF, CaF₂, Al₂O₃ and LiNbO₃ can be machined smoothly by irradiation with laser plasma soft X-rays. Typically, quartz glass is ablated at 40 nm/shot, and has a surface roughness less than 10 nm after 10 shots. In order to investigate lateral resolution, we fabricated a WSi contact mask with 200-nm-pitch line-and-space patterns on quartz glass. We found that quarts glass plates can be machined at a resolution less than 100 nm. In conclusion, we have established a technique for nanomachining a wide variety of inorganic materials using laser plasma soft X-rays at a precision less than 100 nm.