**8. Conclusion**

This chapter briefly reviewed our LPP-EUV source. First, we characterized the source at a wavelength of 13.5 nm with 2% bandwidth as an EUVL source and achieved a maximum CE of 0.9%. When the driving laser power is 110 W at 320 pps, the average power of 1 W is obtained at the wavelength and this is thought to be sufficient for the source to be used in various studies. However, the EUV power required for industrial semiconductor products is more than 100 W at present; our power is two orders of magnitude less. To approach the requirements of an industrial EUV source, the remaining tasks are considered. The majority of Xe plasma debris is fast ions, which can be mitigated using gas and/or a magnetic/electric field relatively easily. The drum system can supply the Xe target for laser pulses with energy up to 1 J at 10 kHz. Therefore, a remaining task is powering up the driving laser. A short pulse laser with average power of the order of 10 kW (i.e., *high average and high peak brightness laser*) must be developed and such a breakthrough is much hoped for.

Not limiting the wavelength to 13.5 nm with 2% bandwidth and using the broad emission at 5–17 nm, a maximum CE of 30% is achieved. Pumping with laser power of 100 W, high average power of 20 W is already obtained and the source is useful for applications other than industrial EUVL using Mo/Si mirrors. We are now applying our source to microprocessing and/or material surface modification. Our source also emits around the wavelength of 6 nm considered desirable for the next lithography source. In conclusion, our LPP source is a practicable continuous EUV source having possibilities for various applications.
