Micromachining of polymethylmethacrylate and polydimethylsiloxane using laser plasma soft X-rays

We have investigated micromachining of polymethylmetacrylate (PMMA) and polydimethylsil-ioxan (PDMS) by irradiation with laser plasma soft X-rays. We generated wide band soft X-rays around 10 nm by irradiation of Ta targets with Nd:YAG laser light. In addition, narrow band soft X-rays at 11 nm and 13.5 nm were generated by irradiation of solid Xe and Sn targets, respectively, with pulsed CO ₂ laser light. The generated soft X-rays were focused on samples, using an ellipsoidal mirror. The soft X-rays were incident through windows of contact masks on the samples. We found that PMMA sheets were ablated by irradiation with soft X-rays at 13.5 nm. PDMS sheets are also ablated by soft X-ray irradiation at 1×10 ⁸ W/cm ², while PDMS surfaces were swelled by irradiation with soft X-rays at 3×10 ⁶ W/cm ². It is remarkable that through holes with a diameter of 1 μm can be fabricated in PMMA and PDMS sheets with a thickness of 4 μm. Thus, we have devel-oped a practical technique for micromachining of PMMA and PDMS sheets in a micrometer scale.