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Extreme ultraviolet (EUV) radiation from laser-produced plasma has been studied for mass-production of the next generation semiconductor devices with EUV lithography. A full set of experimental databases are provided for a wide range of parameters of lasers and targets. These data are utilized directly as a technical guide-line for EUV source system design in the industry as well as used to benchmark the radiation hydrodynamic code, including equation-of-state solvers and advanced atomic kinetic models, dedicated for EUV plasma predictions. Present status of the LPP EUV source studies is presented.

An X-ray fluorescence imaging microscope with a Wolter-type objective mirror (magnification: 13) has been constructed at beamline 39XU of SPring-8. Monochromatic X-rays (DeltaE/E approximately 10(-4)) in the energy range 6-10 keV were used for X-ray fluorescence excitation of the specimens. Using two monochromatic X-rays above and below the absorption edge of a particular element, a two-dimensional image of the element could be obtained. As a result, two-dimensional element mapping of the test specimens (Cu, Co, Ni, Fe and Ti wires) and constituent minerals (Fe, Mn and Ti) of a rock specimen (a piemontite-quartz schist) became possible.

Vacuum ultraviolet (VUV) and soft X-ray measurements are important means of diagnosing impurities in magnetically confined plasmas used in fusion research. Recently, space- and time-resolving flat-field VUV (150–1050 Å) and soft X-ray (20–350 Å) spectrographs have been constructed by using aberration-corrected concave gratings with varied-spacing grooves which give a wide simultaneous spectral coverage on a microchannel-plate intensified detector. Calibration experiments have been performed at beamlines 11A and 11C at the Photon Factory of the High Energy Accelerator Research Organization. The relative efficiency of the VUV spectrograph has been measured for P-polarization geometry in the spectrograph. In the soft X-ray spectrograph, efficiencies have been obtained for several different points of irradiation on the grating along the groove direction and for two (S and P) polarization geometries.

The first result is presented of an X-ray fluorescence microscope with a Wolter mirror in combination with a CCD camera used as an energy-resolved two-dimensional detector in photon-counting mode. Two-dimensional elemental maps of metallic wires, such as Fe, Co, Ni and Cu, and inclusions of a synthesized diamond could be obtained with an energy resolution of 350 eV.

In the development of a high power EUV source used in the EUV lithography system, it is important to understand basic physics of EUV plasma and to optimize laser and target conditions. We have been constructed EUV database of laser-produced tin plasma by the theoretical and experimental studies. On the basis of our understanding, the optimum conditions of lasers and plasmas were clarified, and we proposed the guidelines of laser plasma to obtain clean, efficient and high power EUV source for the practical EUV lithography system. In parallel to such studies, novel targets and high power laser system to generate the optimized EUV source plasma have been developed. Recent progresses of our program are presented.

EUV emission from spherical and planer targets were precisely characterized as an experimental database for use in EUV source generation at high repetition rates. In the single-shot base experiments, conversion efficiency as high as those for the plasma geometry has been demonstrated. The integrated experiment was made with 10 Hz plasma generation, obtained conversion efficiency is low mainly due to unstable positioning of the droplets.

The optimum plasma conditions of extreme ultraviolet (EUV) light source for lithography were experimentally clarified that is optically thin and minimum mass Sn plasma generated from a limited size target. Sn plasma is quite opaque for EUV light of 13.5 nm in wavelength, therefore 13.5 nm light emitted from deep within a Sn plasma is strongly absorbed, thus optically thin plasma production is essential for efficient EUV generation. Contamination of EUV optics caused by debris emanated from laser irradiated Sn targets is a serious problem in the Sn based EUV source system. Target residue around the laser spot is the dominant source of neutral debris, which can be reduced with supplying the minimum mass target containing the minimum number of Sn atoms required for sufficient EUV generation. Spectral purity of generated EUV light is an important requirement to expose clear mask image on a photo-resist film without chromatism. Out-of-band radiation in the vacuum ultraviolet range is dominantly radiated from the laser spot peripheral. Target size must be equal to the laser spot size to suppress the out-of-band radiation.