Research Of13.5nm Extreme Ultraviolet Radiation From Tin Plasma Produced By Laser-assisted Discharge

Extreme Ultraviolet (EUV) lithography is considered to be the most promisingcandidate of next generation lithography. EUV light source is the most importanttechnology of EUV lithography. Of all the technology to produce EUV radiation,laser-assisted discharge plasma (LDP) has got the favor of scientists and is regarded asthe most suitable technology for lithography industry because of high conversionefficiency and collection efficiency of its material-Sn. Unlike the Xe material ofcapillary discharge plasma technology, Sn is solid and must be gasified beforedischarging. So a LDP EUV lithography source is needed. We have designed a newLDP extreme ultraviolet light source device based on an old capillary discharge plasmaEUV light source, and the Sn plasma13.5nm (2%bandwidth)EUV output is gained.The influence of laser energy and delay between laser and main pulse to the EUVradiation output is analyzed, and the best condition of EUV source output is got. This isthe first time for China to get the EUV radiation of Sn, which measures up to advancedworld standard.Theoretically, the source of Sn13.5nm (2%bandwidth) EUV radiation is analyzed,and the Sn8+~Sn12+ion level parameters is calculated using Cowan program to get thespectral distribution of ion energy level transition near13.5nm. Z-pinch theory of Snplasma is described and process of the high ions of Sn is analyzed. We have talkedabout the physical progress in plasma, the radiation related to plasma and broadeningtypes according to the plasma diagnostics. The Boltzmann method is introduced tocalculate the electron temperature, Stark broadening method to calculate the principle ofelectron density.Experimentally, research of electron temperature and density of Sn plasma isintroduced. We have selected three atomic spectrums to calculate the physical state ofSn plasma. It is concluded that electron temperature and density range is small inatmosphere and vacuum environment, along with the change of laser energy and delaytime between the laser and CCD. The average electron temperature of Sn plasma isabout0.6-0.8eV and electron density is about (2.0-2.7)×1017cm-3in the study of energy,and0.7-0.9eV and electron density is about (2.0-2.5)×1017cm-3in the study of delaytime.Equipment of LDP EUV light source and the working process to obtain13.5nmEUV output is introduced. The delay time between laser and the main pulse is analyzedin detail. The influence of delay time between laser and the main pulse is studied to theoutput of EUV source and the best delay time is obtained of about2.5μs. Finally the paper studies the influence of laser energy to the EUV output. It is concluded that theoutput of EUV source is proportional to the laser energy when the energy is less than20mJ, and spectral intensity has nothing to do with the laser energy when the energy isgreater than that.