Pressure-dependent accumulation and ion conversion in hydrogen plasma driven by repetitive pulsed EUV irradiation

In extreme ultraviolet (EUV) lithography, the evolution of EUV-induced hydrogen plasma directly impacts the lifetime and operational stability of optical elements within lithography systems. In this study, a numerical model of EUV-induced hydrogen plasma is developed using a two-dimensional implicit electrostatic particle-in-cell/Monte Carlo collision method. The spatiotemporal evolution of hydrogen plasma under repetitive pulsed EUV irradiation is systematically simulated at background pressures ranging from 2.5 to 10 Pa, with the results compared to the evolutionary characteristics of argon plasma. The simulations reveal that hydrogen plasma exhibits periodic transient dynamics synchronized with the EUV pulses and demonstrates a pronounced pressure-dependent accumulation effect as the number of pulses increases: the higher the background pressure, the stronger the accumulation of plasma density. The evolution of ion composition in hydrogen plasma differs markedly from that of argon plasma: H2+ shows no significant accumulation due to the ultrafast proton transfer reaction, whereas H3+ becomes the predominant ion species during interpulse intervals. During repetitive pulsing, the accumulation of background plasma significantly suppresses space charge separation, resulting in a pulse-by-pulse decrease in the plasma potential amplitude. Furthermore, the peak electron temperature steadily decreases with increasing pulse numbers and can be precisely regulated by adjusting the background pressure. These findings provide theoretical support for controlling plasma effects and protecting optical components in EUV lithography systems.