Laser Produced Plasma X-ray and EUV Sources for Lithography

For Sn based sources, the path to incorporation in a lithography tool is clear. The source of choice will be a Sn liquid droplet source, ideally operating at a 100 kHz repetition rate preionised by a low intensity Nd:YAG prepulse and allowed to expand until it reaches the critical density for CO₂ radaiton when it will be reheated by a CO₂ pulse. The challenges here are tailoring the duration of the CO₂ pulse to match the lifetime of the plasma target when it is at the optimum density for absorption of the 10.6 µm radiation and sustaining the high required repetition rate for both stable droplet injection and laser operation. For 6.x nm based sources a major increase in CE needs to be attained in order to demonstrate the feasibility of that technology as well as the experimental realisation of the theoretical mirror reflectivitis for the LaB4C multilayers. Even then, the design of a droplet injection system will pose a major additional challenge. Should all these difficulties be overcome the power requirement at intermediate focus will probably exceed 1KW because of the increased resolution required on the resist.