Progress Toward use of a Dense Plasma Focus as a Light Source for Production EUV Lithography

摘要

Recent advances in the Dense Plasma Focus (DPF) under investigation by Cymer as an EUV light source have increased both the total energy storage capacity and the peak drive current. Previous generation DPF tools built by Cymer produced no measurable EUV radiation while employing Xenon as a source gas, but instead employed Lithium vapor due to its higher emission efficiency at low plasma temperatures. With Xenon as a source gas, this generation DPF exhibits efficiency similar to other sources employing direct electrical drive of the Xenon plasma. An emission efficiency of greater man 0.20% has been measured into 2πstr and a 2% bandwidth centered at 13.5nm. Other characteristics of this DPF have been measured such as energy stability, spectrum, source size, position stability, and operation at high repetition rates. In addition, the out-of-band radiation in the UV/Vis region (130nm-1300nm) has been measured and found to be only 0.38% of all radiation emitted by this source. Such low out-of-band radiation opens up the possibility of eliminating the Spectral Purity Filter and the problems associated with its use. This source concept does not use a multi-layer dielectric mirror as the first collector, but instead employs a grazing incidence collector mat is more tolerant to debris. Progress has been made in the fabrication quality of this optic. Recent measurements of prototypes show that this optic will not degrade me source brightness. Also, a more efficient design has been created that consist of two shells coated with Ruthenium. This design collects and re-images 18.6% of the EUV radiation emitted into 2πstr.