[18p-A404-1~12] Progress in studies on mterial conversion and processing with high-power lasers

[18p-A404-4] Material processing by laser driven high power pulsed EUV radiation with improved debris mitigation

〇(PC)Nozomi Tanaka¹, Nao Wada¹, Yasuyuki Kageyama², Hiroaki Nishimura¹ (1.ILE, Osaka Univ., 2.TOYOTA CRDL, INC.)

Keywords:Extreme ultraviolet radiation, Material processing, Debris mitigation

Extreme ultraviolet (EUV) radiation at wavelength ranging from few to several tens of nanometers has attracted much attention as a material processing method for wide-band-gap or insulator materials. Laser produced plasma EUV source emits intense pulsed EUV radiation with high conversion efficiency. Such properties are advantageous for industrial use. However, a drawback is the debris accumulation on the materials and it must be minimized for applying the EUV source to material processing. The debris particles are originated from the EUV source target and sputtered optics. We have designed a low-cost debris mitigation system by exploiting the difference in the particle trajectory and the EUV optical path. The expanding EUV light from a point plasma source is focused at the intermediate focal point by the first elliptical toroidal mirror coated with Au, then EUV light expands towards the second toroidal mirror. The sample material is located at the second focal point and is ablated by the intense pulsed EUV light. We have installed a debris shield with a 3 mm aperture around the intermediate focal point. While the EUV light passes through the aperture, the shield cuts off most of the plasma particles or scattered particles from the toroidal mirror due to their wide angular distributions. Further, energetic particles that cause mirror sputtering lose their kinetic energy by the collision with the mirror surface, and second mirror does not get sputtered much. We have evaluated the debris mitigation ability of the system by experiments of Si thin film deposition and two-body collisional simulation by TRIM code. The mass ratio of debris elements was under the detection limit of x-ray fluorescent analysis, while almost half of mass ratio was debris without the debris mitigation system. The simulation results showed that the Au particles sputtered from the first toroidal mirror are reduced by three orders of magnitudes at the sample material, and Xe particles are also reduced by three orders of magnitude at the entrance of second toroidal mirror. This study showed the debris mitigation ability of the designed system. The detailed quantitative data and discussion will be presented.