Characteristics of Extreme Ultraviolet and Debris Emission From Laser Produced Bi Plasma
XIE Zhuo1, 3, WANG Hai-jian1, DOU Yin-ping1*, SONG Xiao-wei1*, LIN Jing-quan1, 2
1. School of Physics, Changchun University of Science and Technology, Changchun 130022, China
2. Jilin Provincial Key Laboratory of Ultrafast and Extreme Ultraviolet Optics, Changchun University of Science and Technology, Changchun 130022, China
3. Chongqing Research Institute, Changchun University of Science and Technology, Chongqing 401120, China
Abstract：Laser produce plasma extreme ultraviolet (EUV) source, which has the advantages of small size, high stability and adjustable output wavelength, plays a significant role in applying EUV lithography. Laser produces plasma Bi EUV source has a wide spectrum in the wavelength range of 9~17 nm, which can be used to apply extreme ultraviolet metrology in the development of extreme ultraviolet lithography. Therefore, EUV emission and debris characteristics from laser-produced Bi plasma were carried out. When the 1 064 nm pulse laser irradiated the Bi target, a natural dip displays at 12.3 nm in the EUV spectrum, corresponding to the L-edge absorption in silicon. Meanwhile, two strong peak emissions are located at 11.8 and 12.5 nm, respectively. Firstly, we studied the emission characteristics and intensity of the spectrum near the 11.8 and 12.5 nm dependence on laser power density. When the laser power density is adjusted by changing the focus spot size by fixing the laser energy, the emission intensity of two peaks increases first and then decreases with an increase in the laser power density. The maximum emission intensity of two peaks was formed when the laser power density of 2.0×1010 W·cm-2. This is attributed to the final output EUV emission is determined by the balance of the laser energy loss used to support plasma expansion and reabsorption of the EUV emission by the plasma. When the laser power density is adjusted by changing laser energy by fixing the focus spot size, the emission increases with an increase of laser power density due to the ablation material and high stage ions increases. Secondly, we studied the effect of dual pulse on the emission intensity of the 11.8 and 12.5 nm peaks. The experiment results show that the emission intensity of two peaks increases gradually when the laser energy increases from 20~140 mJ. Moreover, the intensity decreases when the laser energy larger than 140 mJ due to the EUV emission being absorbed by the thick plasma at a larger plasma density. In addition, it is found that the dip generated in the spectrum at a 13~14 nm wavelength with a single pulse laser disappeared when using the dual pulse method. Finally, we measured the angular distributions of ions emission from a 1 064 nm laser-produced plasma. The results indicated that the kinetic energy of Bi ions decreases when the detection direction moves from the normal direction of the target surface to the direction along the target surface due to the plasma preferential expansion perpendicular to the target surface. Moreover, the kinetic energy of Bi ions decreases linearly with the decrease of laser pulse energy. This research is expected to provide technical support and lay a solid foundation for the metrology field needed in the development of EUV lithography.
Key words：Laser produce Bi plasma; Extreme ultraviolet emission; Dual pulses; Ion debris
谢 卓，王海建，窦银萍，宋晓伟，林景全. Bi靶激光等离子体极紫外光源以及碎屑辐射特性研究[J]. 光谱学与光谱分析, 2022, 42(07): 2056-2062.
XIE Zhuo, WANG Hai-jian, DOU Yin-ping, SONG Xiao-wei, LIN Jing-quan. Characteristics of Extreme Ultraviolet and Debris Emission From Laser Produced Bi Plasma. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2022, 42(07): 2056-2062.
