Progress report on a 14.4-nm micro-exposure tool based on a laser-produced-plasma: debris mitigation system results and other issues

Within a National Project on nanotechnologies, a Micro-Exposure Tool (MET) for projection lithography at 14.4 nm, based on a laser-produced plasma source, is being developed at the Frascati ENEA Center. The choice of this “exotic” wavelength is due to the higher efficiency of a Debris Mitigation System (DMS) working in the interval of approximately 14 nm - 15 nm. It has to be noted that Mo/Si multilayer mirrors (MLM) can still have a high reflectivity also at these wavelengths. The solid-tape-target laser-generated plasma is driven by a XeCl excimer laser, with an optimized intensity of about 310^10 W/cm^2, generating an extreme ultraviolet (EUV) source with a diameter of about 0.2 mm. Clearly, this kind of source emits a lot of debris (both atomic and particulate types) and the 7-cm-far collector mirror must be protected against them. The paper is mostly devoted to the accurate and systematic study of these debris and to their reduction. The results of mitigation efficiency obtained with a DMS prototype are very encouraging and lead to the design and patenting of its improved version.