Liquid Droplet Jet Target Laser Plasma Soft X-ray Source

In this dissertation, we mainly report on a laser-produced plasma (LPP) source with liquid aerosol spray target. For sufficiently high backing pressure and low temperature, the valve reservoir gas of the light source can undergo a gas-to-liquid transition. Upon valve opening, the liquid is ejected into a vacuum and breaks into micron-sized droplets, which is an attractive target for soft X-ray and extreme ultraviolet (EUV) sources using lasers with nanosecond pulse width. Such laser-driven droplets sources are presently being considered as EUV sources for next generation projection lithography and soft X-ray radiation metrology.Firstly, by the use of Cowan program on the basis of non-relativistic quantum mechanics, we have computed the radiative transition wavelengths and probabilities in soft X-ray region for O4+, O5+, O6+, O7+, F5+, F6+, F7+, Kr6+, Xe6+ ions which are correspondingly produced from the interaction of 1011~1012W/cm2 power laser with liquid O2, CO2, CF4, Kr and Xe spray targets. The goal is to theoretically research the spectrum characterization of above-mentioned liquid targets in given laser energy range and to select a suitable target material for EUV projection lithography(EUVL).Secondly, investigation on several key parameters like laser wavelength, pulse duration and power density have been carried out for the purpose of optimizing radiation from various liquid aerosol spray targets.Thirdly, we developed a spectrometer for spectrum diagnosis of soft X-ray pulse sources, and used it to measure spectra of liquid O2, CO2, CF4, Kr and Xe spray target LPP sources in 6-20nm band for 8X 10uW/cm2 laser irradiance The results coincide with Cowan calculation fairly well.Xenon is identified as a promising target material for EUVL, based on both high EUV intensity measured in 13-14nm and no condensation on multiplayer mirror surfaces due to chemical inert. For liquid Xe aerosol spray target, Important LPP characteristics, such as laser-to-EUV conversion efficiency, EUV radiation absorption, debris production by target material erosion or deposition, are studied in detail, a 13.4nm conversion efficiency of 0.75% into 2% bandwidth and 2 π steradian emission solid angle is achieved at 0.5mm laser-nozzle distance. Experiments of debris comparison have been also done, the results show that the liquid Xe aerosol spray target LPP source almost eliminates debris after 105 laser shots.Finally, we rebuild a soft X-ray reflectometer in 8-30nm region by replacing its metal target with low-debris Kr and Xe aerosol spray targets. Reflectivity of soft x-ray multilayer mirrors are measured by the new reflectometer, and the results show the accuracy is about ±2%%.