Focusing electrode effect on the EUV lighting technology based on C-beam irradiation technique

One of the key issues in large-scale semiconductor manufacturing is EUV (extreme ultraviolet) lighting source technology [N. Fu, Y. Liu, X. Ma, and Z. Chen, J. Microelectron. Manuf. 2, 1 (2019); I. Fomenkov et al., Adv. Opt. Technol. 6, 173 (2017); J. Beckers, T. van de Ven, R. van der Horst, D. Astakhov, and V. Banine, Appl. Sci. 9, 2827 (2019); V. Y. Banine, K. N. Koshelev, and G. Swinkels, J. Phys. D: Appl. Phys.J. Phys. D. Appl. Phys. 44, 253001 (2011)]. We have previously demonstrated the use of a cold cathode electron beam (C-beam) for the EUV lighting source [S. T. Yoo and K. C. Park, Nanomaterials 12, 4134 (2022); S. T. Yoo and K. C. Park, Jpn. J. Appl. Phys. 62, SG1002 (2023); B. C. Adhikari, S. T. Yoo, and K. C. Park, in 2023 7th IEEE Electron Devices Technology and Manufacturing Conference, Seoul, South Korea, 7 -10 March 2023 (IEEE, New York, 2023), pp. 1–3]. However, advancing the next generation of EUV lighting with C-beam irradiation requires improvements in beam spot size, EUV efficiency, and lighting power, as identified in our earlier studies. To address these issues, we implemented a focusing electrode technique [B. C. Adhikari, B. Ketan, R. Patil, E. H. Choi, and K. C. Park, Sci. Rep. 13, 15630 (2023)]. This approach improves the beam’s spot size and brightness without reducing the anode current. By measuring transmittance under different anode and focusing bias conditions, we identified the optimal focusing electrode bias that avoids electron reflection between the focusing electrode and the beam. As a result, we achieved a 4.8 times reduction in beam divergence angle and a 34% increase in brightness, measured by gray value on a phosphor screen, without any loss of anode current. Additionally, by increasing the anode current density with a focusing electrode, we observed a 23.7% improvement in EUV photocurrent as measured with a photodiode equipped with a Zr filter (300 nm) [F. R. Powell and T. A. Johnson, in Emerging Lithographic Technologies V, Santa Clara, California USA, 25 February-2 March 2001 (SPIE, Bellingham, 2001), pp. 585–589; N. I. Chkhalo et al., in International Conference on Micro- and Nano-Electronics 2009, Zvenigorod, Russia, 5-9 October 2009 (IEEE, New York, 2010), pp. 49–57]. These findings highlight the potential of developing an EUV inspection tool based on the C-beam irradiation technique by integrating the focusing electrode.