Katsutomo Terashima

Billion-level durable ArF excimer laser with highly stable energy

We have succeeded in the development of the ArF excimer laser with high performance and durability, by researching and developing of the spectral measurement and gas control technologies, laser chamber with radio frequency preionizer, the high repetition rate solid state pulse power module and the optimized highly durable optical module. As regards spectral measurement technologies, the true instrumental function of a monitor etalon have been measured by our developed 193nm coherent light source. Spectrum of ArF laser could be obtained precisely by deconvolution performed using the covolved spectrum of the ArF laser and the measured instrumental function of the monitor etalon. As for gas control technologies, the influence of impurities given to the ArF laser performance was bigger about 5-20 times compared with the KrF one. And we have paid attention that low concentration Xe gas has effect to the triple output energy. The durability test of 2 billion pulses has been done for the first time in the world. The developed ArF laser kept the integrated energy stability less than +/- 0.6 percent and spectral band-width of FWHM less than 0.8 pm. The result showed, developed laser has an enough performance for lithography even after the pulse number exceeds 2 billion pulses.

Performance Improvement of a Discharge-Pumped ArF Excimer Laser by Xenon Gas Addition

The effect of xenon (Xe) gas addition to a discharge-pumped ArF excimer laser was examined. When the partial pressure of the Xe gas was changed over a wide range, the output energy of the ArF excimer laser was found to become maximum at the Xe partial pressure of 20 mTorr and to be about three times higher than that without Xe addition. It was shown that Xe gas addition was effective in increasing the initial electron density which was produced in the preionization process, and that the increase of the initial electron density then produced a tendency to make the main discharge in the laser uniform in the direction of the optical axis.

Ultra line-narrowed ArF excimer laser G42A for sub-90-nm lithography generation

193-nm lithography is going to move from pre-production phase to mass production phase and its target node become narrowing from 90 nm to 65 nm. In these situations, the laser manufacture needs to provide the high durable ArF excimer laser, which has superior spectrum performance. Gigaphoton has already introduced 4 kHz ArF laser (model G41A) to 193-nm lithography market, which produce 20 W and spectrum bandwidth of 0.35 pm (FWHM). G41A has showed high reliability and long lifetime over 5 billion pulses. In this paper, we report on the 4 kHz ArF excimer laser for mass production, model G42A, which has 20 W, spectral bandwidth less than 0.3 pm (FWHM) and a spectral purity less than 0.75 pm (E95).

Ultranarrow-bandwidth 4-kHz ArF excimer laser for 193-nm lithography

We have developed a 4-kHz ArF excimer laser with ultra-narrow bandwidth, which is applicable to high-NA scanners for sub-0.13-micrometers microlithography. In this paper, we describe a 4-kHz ArF excimer laser for mass production: the model G40A, which has an output power of 20 W and energy dose stability of less than +/- 0.3% (20-ms window) at 4 kHz. This dose stability is comparable to the performance of an existing 2-kHz ArF excimer laser, the model G20A. The new laser also has the following specifications: a long pulse duration of over 40 ns, spectral bandwidth of less than 0.35 pm (FWHM), and spectral purity of less than 1.0 pm (95%). These characteristics are better than those of the G20A. A lifetime test of over 7 billion pulses has been conducted at 4-kHz operation. The new laser has maintained an energy dose stability of less than +/- 0.3% (20-ms windows) and demonstrated performance suitable for mass production even after over 7 billion pulses.

Output stabilization technology with chemical impurity control on ArF excimer laser

Based on accurate gas analysis technology it has been found that both gas purity and gas control are key factors in optimizing the performance of ArF excimer lasers. The study of the behavior of gas impurities inside the laser chamber showed that impurities built up not only during laser operation but also during rest periods. In-situ gas analysis and controlled impurity gas addition clarified that hydrogen fluoride and oxygen impurities, are the main causes for the decrease of laser output energy. Based on our experiments, a modified gas composition was chosen for the ArF laser that significantly improved its output characteristics.

Highly durable low CoO mass production version of 2-kHz ArF excimer laser for DUV lithography

We have succeeded in the commercialization of the worlds first kHz ArF excimer laser for microlithography application. The ArF laser is expected to be the light source for the DUV lithography tools for sub-0.13 micron geometry semiconductor production. In this paper, we present the performance and advanced technologies of the newest model of the ArF excimer laser, which achieves 10W of output power with 0.5 pm bandwidth at 2 kHz. The pulse-to-pulse energy stability, 3 sigma is less than 10 percent and integrated energy stability is within +/- 0.3 percent. The durability performance is extended to 5 billion pulses, which provides affordable CoO for volume production.

High-repetition-rate ArF excimer laser for microlithography

ArF excimer lasers are the light source of choice for the next generation of micro-lithographic tools enabling structures below the 130nm technology node. For these lithographic mass production lines Komatsu successfully developed an ArF excimer laser, named G20A, which has a 2kHz pulse repetition rate, 10W average power and 0.5pm (FWHM) spectral bandwidth. G20A has three significantly improved important items: (1) the high resolution line narrowing module, (2) the high power and high repetition rate solid state pulse power module, and (3) the Xe added laser gas yielding an improved overall laser performance. ArF laser spectra were determined with out newly developed high-resolution spectrometer. The instrument function of the spectrometer was measured with a 193nm coherent light source jointly developed with the University of Tokyo. The laser gas composition is one key parameter of excimer laser performance. The deteriorating effect of impurities on ArF performance is e.g. ten times larger than on KrF performance. We observed that added Xe gas, however, has a beneficial effect on the pulse energy and the energy stability at high repetition rates. Experimental results of a currently developed 4 kHz ArF laser are also reported.

1-kHz 5-W ArF excimer laser for microlithography with highly narrow 0.7-pm bandwidth and issues on durability related to optical damage

We present the result of billion level durability test in the newest model of ArF excimer laser, KLES-G5A, for microlithography and durability issues relate to optical damage. The developed ArF laser achieves 5 W of output power with integrated energy stability less than +/- 0.3 percent at 1 kHz repetition rate. The spectral characteristic by FWHM of the deconvolved spectrum is less than 0.7 pm and the 95 percent energy of the total energy is within 2.0 pm band, which is designed to be suitable for partially achromatized refractive projection optics. Durability test of 1 billion pulses has already finished, and we have observed very slight changes in the performance. Prior to the durability test, irradiation examinations have been done. It demonstrates that CaF2 material has superior stability to SiO2 even as the high fluence DUV optical parts of line-narrowed ArF laser.