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Influence of a laser intensity on EUV brightness and ion speed from a laser-assisted discharge-produced plasma

 

Extreme ultraviolet (EUV) source is utilized in the cutting-edge semiconductor manufacturing process. Ushio has been delivering Laser-assisted Discharge-produced Plasma (LDP) source for EUV mask inspection. In this source, the discharge is triggered by irradiating a pulsed laser to the electrode coated with a liquid tin. During the discharge, the plasma self-compression, called pinch phenomenon, generates the hot and dense tin plasma, which emits EUV. In general, plasma sources emit not only the light but also the fast ions. The ions having a high kinetic energy damage the optics dedicated to EUV. Therefore, we need to understand the characteristics of EUV and fast ion. EUV and fast ion generation in the LDP source strongly depends on the trigger-laser condition because it defines the initial condition of the discharge. We investigated that the influence of the laser intensity on EUV emission and the kinetic energy of ions. The experimental results suggested that the laser intensity higher than 25 GW/cm² produced high EUV brightness and reduced ion kinetic energy.


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