In the development of extreme ultraviolet (EUV) light source for EUV lithography systems by laser-produced plasma (LPP), reduction of debris emitted from the plasma such as ions, droplets and neutral atoms is one of the most important factors. In our study, we developed a two-dimensional (2D) laser-induced fluorescence (LIF) imaging system for neutral atoms from the plasma and investigated neutral debris behaviors in order to obtain the guideline for the optimization of debris shields. Dependence of atomic emission on a thickness of LPP Sn target film was observed and the distributions of emitted neutral atoms in H2 gas were measured by 2D LIF system.
EUV lithography is scheduled on the international technology roadmap for semiconductors (ITRS). In order to introduce the EUV light source into the production lines, EUV light sources having an average power of more than 100 W at 13.5 nm are needed. Such EUV light sources have been under development by using the laser-produced plasma (LPP) or the discharge-produced plasma (DPP). In the case of Sn LPP, the efficiency is several times higher than that of Xe LPP, but the problem of debris generation that limits the lifetime of the optics in the lithographic system is serious. The mechanism of debris generation is considered to be splashes of a melted surface by rapid heating of the sub-surface within a depth of about 100 nm. So we have suspected that the nano-particles with a diameter of less than 100 nm produce no debris, because the sub-surface can not be produced within such a small particle. In this study, we developed nano-structured SnO2 targets and investigated the emission characteristics of EUV light from CO2 laser produced plasma with those targets.
We propose CO2 laser-produced plasma as the extreme ultraviolet (EUV) light source for future optical lithography. The laser beam from a transversely-excited atmospheric (TEA) CO2 laser (4 J, 50 ns FWHM) was focused on a Xe gas target and a Xe cryogenic target to generate EUV radiation around 13.5 nm. The EUV pulse of about 100 ns in FWHM was measured 50 ns after the CO2 laser irradiation. The EUV spectra were measured by an X-ray CCD camera with a transmission grating spectrograph (TGS). A characteristic EUV spectrum was observed from CO2 laser produced Xe plasma. The EUV energy was measured by a Flying Circus II detecting system and an output energy of 3 mJ/pulse and a conversion efficiency of about 0.1% per 2π sr at 13.5 nm (2% B.W.) were obtained with Xe targets. These values are comparable to those of YAG laser-produced Xe plasma, indicating the potential scalability of the EUV light source using a CO2 laser produced plasma.
We propose CO2 laser-produced plasma as the extreme ultraviolet (EUV) light source for future optical lithography. The laser beam from a transversely-excited atmospheric (TEA) CO2 laser (4 J, 50 ns FWHM) was focused on a Xe gas target, a Xe cryogenic target and a nano-structured tin-based target to generate EUV radiation around 13.5 nm. The EUV pulse of about 100 ns in FWHM was measured 50 ns after the CO2 laser irradiation. The EUV spectra were measured by an X-ray CCD camera with a transmission grating spectrograph (TGS). A characteristic EUV spectrum was observed from CO2 laser produced Xe plasma. The EUV energy was measured by a Flying Circus II detecting system and an output energy of 3 mJ/pulse and a conversion efficiency of 0.2% per 2π sr at 13.5 nm (2% B.W.) were obtained with Xe targets. These values are comparable to those of YAG laser-produced Xe plasma, indicating the potential scalability of the EUV light source using a CO2 laser produced plasma.
We have developed an ultra-line-narrowed, high-repetition-rate, high-power injection-locked F2 laser system for 157 nm dioptric projection systems under the ASET project “F2 Laser Lithography Development Project”. A spectral bandwidth of < 0.2 pm (FWHM), an output power of > 25 W, and an energy stability (3-sigma) of < 10 % at 5 kHz repetition rate was successfully obtained by using a low-power ultra-line-narrowed oscillator laser and a high-gain multi-pass amplifier laser. These parameters satisfy the requirements of exposure tools. A numerical simulation code that can simulate the spectral dynamics of the F2 laser under different operation modes such as free running operation, line-narrowed operation, and injection-locked operation, has also been developed. Using this simulation code, it is found that the instantaneous spectral bandwidth narrows monotonously during the laser pulse, and a narrower spectral output can be obtained by seeding the tail area of the line-narrowed F2 laser pulse. And the line-narrowing operation of the oscillator laser and the behavior of the injection-locked laser system can be predicted very precisely with this simulation code. The development of F2 laser for microlithography will be accelerated by this new simulation code.
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