Ionic interactions around EUV generating tin plasma
Extreme ultraviolet (EUV) light is used by state-of-the-art nanolithography machines to create microchips that are eventually used in many electronic devices including smartphones, laptops, etc. The EUV light is generated by irradiating molten Sn microdroplets with a high-power pulsed laser, which creates the hot, dense laser produced plasma (LPP) that emits EUV light. However, during this process undesirable products such as energetic Sn ions are also produced which, if not controlled, may damage the expensive multilayer optics in the machine, particularly the EUV collector mirror. To prevent this, the LPP is embedded in H2 gas as it is transparent to EUV light but stops the energetic Sn ions. The fundamental understanding of Sn-H2 collision processes such as charge exchange, stopping etc. is essential for creating predictive ion-stopping models. Understanding the interactions and tolerances of multilayer optics materials, such as Mo and Ru, to the impact of heavy Sn ions is also necessary to determine the optimum concentration of H2. However, fundamental data on all these significant processes occurring inside the LPP-EUV source is scarce. In this work, the interactions of Sn ions with H2 gas and solid surfaces at keV energies have been investigated therefore adding new data and insights into the collisions of Sn ions with surface and gas targets relevant to EUV nanolithography. Existing simulation codes for modeling ion stopping have been benchmarked for heavy projectiles such as Sn ions, and novel data on charge exchange in Sn – H2 collisions, have been generated.