EUV-induced plasma: PIC modelling of a transient plasma fluxes

Extreme Ultra Violet (EUV; 13.5 nm) is used to image patterns onto wafers in high-end semiconductor manufacturing. The EUV photons have sufficient energy (92 eV) to ionize the hydrogen gas inside the lithography tools. This EUV-induced plasma has various positive and negative effects, ranging from material etching and degradation, to electrostatic particle deflection. These effects are complicated by the pulsation of the EUV light; it comes in short pulses: 100 ns of light each 20 µs (50 kHz). Therefore, the EUV-induced plasma is never in steady state, but always transient shifting between bursts of high-energy electrons (up to 78 eV) and decaying afterglow. We investigate this plasma and its effects using a dedicated 3D Particle-In-Cell (PIC) model.

In this contribution, we focus on the ion flux to a pellicle inside a lithography tool. A pellicle is a very thin freestanding membrane (centimeters in size, but only tens of nanometers thick), which protects the photomask from particulates. It is extremely thin to minimize EUV loss by absorption, but this makes it vulnerable for plasma degradation. Hence, it is crucial to know the ion fluxes to this pellicle both to predict and improve its lifetime. Our PIC modelling results show fluxes of high energetic ion for ~500 ns in between decaying low energy flux for 20 µs. The resulting ion energy spectrum is used as input for material choices and testing strategies that will enable semiconductor manufacturing for the upcoming <3 nm nodes.