Research On The Characteristics Of Laser Produced Sn And SnO₂ Plasma

Extreme ultraviolet lithography?EUVL? with a wavelength of 13.5 nm is widely considered as one of the most promising technologies for the next generation of lithography?NGL? in the world. Laser produced plasma?LPP? is considered as one of the most potential solutions to get EUVL light source since it has several advantages such as the debris control, high conversion efficiency, small size of light source, and so on. With the advance of extreme ultraviolet lithography, the research of EUV source for meteorology also plays important role. The appropriate target and the drive laser are the keys to improve the output power and reduce the ion debris of LPP.In the dissertation, the characteristics of ion debris and EUV emission from laser produced Sn and Sn O₂ plasma with different wavelength lasers have been comparatively studied. The effects of magnetic field and the pre-pulse laser on Sn plasma parameters and EUV emission also have been investigated.Firstly, the characteristics of Sn and Sn O₂ plasma produced by pulse CO₂ laser and Nd: YAG laser, and their EUV emission have been studied, respectively. The characteristics of plume expansion and ion debris from both Sn and Sn O₂ plasma were studied based on the direct imaging and the time of flight?TOF? methods. The time evolution of the path length and the ion kinetic energy from both plasmas were calculated from ICCD images. The spread angular distributions and the most probable expansion speed of ion debris emitted from both CO₂ laser plasmas and Nd: YAG laser plasmas were also compared. It was found that the ion kinetic energy of Sn O₂ plasma is higher. Additionally, the number density of plasma particles were supposed to be in Shifted Maxwell–Boltzmann distribution and were fitted to ion time of flight time spectra of Nd: YAG laser produced Sn and Sn O₂ plasmas. From the fitting, we obtained the elliptical kinetic temperatures and the average velocity of the plasma. By the optical emission spectroscopy?OES?, the spectral emission and plasma parameters of Sn and Sn O₂ plasmas have been investigated. The results showed that the electron temperature and density of Sn O₂ plasma are larger with the same incident laser. And the electron temperature and density of Nd: YAG laser plasma are larger.Secondly, in the section of the EUV radiation, the EUV radiation characteristics of Sn and Sn O₂ plasmas produced by CO₂ and Nd: YAG lasers were studied using the grazing incidence grating spectrometer. And through the EUV radiation spectrum, the conversion efficiency?CE? were also calculated and it was found that the EUV CE of Sn O₂ plasma is relatively low. With the EUV photodiode?IRD?, the time and space distribution characteristics of different laser produced plasmas were measured and analyzed. The angular distribution of EUV radiation was expressed as a function of the opacity using the Beer–Lambert law. The results showed that the EUV radiation, which was generated from CO₂ laser, have longer duration, and it also has more uniform spatial distribution.Finally, the effects of an external magnetic field and the pre-pulse laser on Nd: YAG laser produced Sn plasma have been investigated. Under the influence of the magnetic field, the characteristics of ion debris from Sn plasma, emission spectra and the EUV radiation have been studied in detail. The results showed that the ion kinetic energies of the plume species can be effectively reduced with a modest magnetic field of 0.6 T. And we also have found that it was not any inflence of magnetic field on the time and space characteristics of EUV emissions. Furthermore,the effect on the ion debris and the EUV radiation of CO₂ laser reheating the initial plasma produced by Nd: YAG pre-pulse laser were investigated. The pre-pulse laser intensity and the delay timings between the pre-pulse and main pulse were varied to determine the optimum conditions for reducing the ion debris and enhance the EUV CE. The results showed that the EUV CE increased by 50%.