Optimization of extreme ultra-violet light emitted from the CO2 laser-irradiated tin plasmas using 2D radiation hydrodynamic simulations

We studied Extreme Ultra-Violet (EUV) emission characteristics of the 13.5 nm wavelength from CO2 laser-irradiated pre-formed tin plasmas using 2D radiation hydrodynamic simulations. Our results indicate that when a CO2 laser irradiates pre-formed tin plasma, the heated plasma expands towards the surrounding plasma, steepening the density at the ablation front and lowering the density near the laser axis due to the transverse motion of the plasma. Consequently, the laser absorption fraction decreases, and the contribution to EUV output from the ablation front becomes dominant over that from the low-density plasmas. We estimated that an EUV conversion efficiency of 10% from laser to EUV emission could be achieved with a larger laser spot size, shortened laser pulse width, and longer pre-formed plasma density scale length. Our results offer one optimizing solution to achieve an efficient and powerful EUV light source for the next-generation semiconductors.