Experimental investigation of debris mitigation in discharge produced EUV light source

Summary form only given. For realizing extreme ultraviolet (EUV) lithography, a debris free EUV source with collectable radiation power of about 115 W and repetition rates exceeding 7-10 kHz will be required. Discharge produced plasma is one of the promising radiation source for achieving the required parameters. However, it has a problem of debris generation, which is due to the melting and evaporation of electrodes and a capillary caused by the excess input of heat into their surfaces and the fact that the pinching plasma interacts more strongly with the insulator surface than others. In present study, in order to overcome these difficulties and to satisfy the source requirements, a capillary Z-pinch discharge light source has been made and demonstrated. Our device is equipped with a water-cooled ceramic capillary and electrodes, and a solid state pulsed power generator. A stacked static induction thyristors are used as switching elements, which enable high repetition rate operation of pulsed power supply. A magnetic switch is connected in series, which not only assists the semiconductor switch but also provides a preionization current. It has been confirmed that the duration of preionization current can be controlled by amplitude of offset current flowing through magnetic switch and that the preionization is essential to generate a uniform and stable plasma. For mitigating debris, the gas curtain system, which is consisted of supersonic nozzle and diffuser, has been installed. The properties of the radiated EUV light will be discuss. Also, preliminary experimental results of gas curtain system will be shown.