ArF immersion technology is spotlighted as the enabling technology for the 45nm node and beyond. Recently, double
exposure technology is also considered as a possible candidate for the 32nm node and beyond. We have already released
an injection lock ArF excimer laser, the GT61A (60W/6kHz/10mJ/0.35pm) with ultra line-narrowed spectrum and
stabilized spectrum performance for immersion lithography tools with N.A.>1.3, and we have been monitoring the field
reliability data of our lasers used in the ArF immersion segment since Q4 2006. We show GT series reliability data in the
field. GT series have high reliability performance. The availability that exceeds 99.5% proves the reliability of the GT
series. We have developed high power injection lock ArF excimer laser for double patterning, the GT62A
(90W/6000Hz/15mJ/0.35pm(E95)) based on the GigaTwin (GT) platform. Number of innovative and unique
technologies are implemented on GT62A in order to reduce running cost of laser. We have introduced unique technology
to enable 40 billion pulse lifetime of laser chambers to drastically reduce running cost. In addition, we have improved
lifetime of Line Narrowing Module significantly by changing optical path. Furthermore, the extension of gas refill
intervals was achieved by introducing new gas supply module and sophisticated gas control algorithm. We achieved the
reduction of operation cost and down time by introducing these three technologies.
In advanced lithography processes, immersion lithography technology is beginning to be used in volume production at
the 45-nm technology node. Beyond that, double-patterning immersion lithography is considered to be one of the
promising technologies -meeting the requirements of the next-generation 32-nm technology node. Light source
requirements for double patterning lithography tool are high power and high uptime to enhance economic efficiency, as
well as extremely stable optical performances for high resolution capabilities.
In this paper, the GT62A, Argon Fluoride (ArF) excimer laser light source which meets these requirements is introduced.
The GT62A has an emission wavelength of 193-nm, a power output of 90 W and a repetition rate of 6,000 Hz. The dose
uniformity of the GT62A was improved for reduction of Critical Dimension (CD) variation and better Critical
Dimension Uniformity (CDU). A stable wavelength and a spectrum bandwidth of the GT62A satisfy the requirements of
the high resolution lithography tools which need the steady focus stability. In addition, we verified by simulation that the
spectrum bandwidth control in the GT62A contributes to Depth of Focus (DOF) enhancement. The new technology for
the light source and detailed optical performance data are presented.
ArF immersion technology is spotlighted as the enabling technology for below 45nm node. Recently, double exposure
technology is also considered for below 32nm node. We have already released an injection lock ArF excimer laser with
ultra-line narrowed and stabilized spectrum performance: GT61A (60W/6kHz/ 10mJ/0.35pm) to ArF immersion market
in Q4 2006. The requirements are: i) higher power ii) lower cost of downtime for higher throughput iii) greater
wavelength stability for improved overlay and iv) increased lifetimes for lower operation costs.
We have developed high power and high energy stability injection lock ArF excimer laser for double patterning: GT62A
(90W/6000Hz/15mJ/0.35pm) based on the technology of GT61A and the reliability of GigaTwin (GT) platform. A high
power operation of 90W is realized by development of high durability optical elements. Durability of the new optics is at
least 3 times as long as that of the conventional optics used in the GT61A. The energy stability is improved more than
1.5 times of performance in the GT61A by optimizing laser operational conditions of the power oscillator. This
improvement is accomplished by extracting potential efficiency of injection lock characteristic. The lifetime of power
oscillator, which is one of the major parts in cost of ownership, is maintained by using higher output of the power supply.
The Argon Fluoride (ArF) immersion lithography is now shifting to mass production phase for below 45nm node. For a
laser light source in this node, narrower and more stable spectrum performance is required. We have introduced GT61A
ArF laser light source (60W/6kHz/10mJ/0.35pm) with spectrum E95 stabilization system which meets these
requirements. The narrow and stabilized spectrum performance was achieved by developing an ultra line narrowing
module and Bandwidth Control Module (BCM). It contributes to the reduction of differences of the spectrum during
exposure over a wafer, wafer to wafer, during machine lifetime and machine to machine for every light source. Stable
laser performance is obtained for mass production. The GT61A integrated on a common and already reliability-proven
GigaTwin (GT) platform, and its inherited reliability is proved with the availability over 99.5% in the field.
The GT61A ArF laser light source with ultra line narrowed spectrum, which meets the demand of hyper NA (NA > 1.3)
immersion tool, is introduced. The GT61A aims at improving spectrum performance from value E95 0.5pm of GT60A.
The spectrum performance 0.3pm or less was achieved by developing an ultra line narrowing module newly.
Moreover, in 45nm node, since it indispensably requires OPC (optical proximity correction) and a narrower process
window, improved stabilization of spectrum performances was performed by bandwidth control technology. Newly
designed Bandwidth Control Module (BCM) includes high accuracy measurement module which support the narrower
bandwidth range and active bandwidth control module. It also contributes to the reduction of the tool-to-tool differences
of the spectrum for every light source.
Last year Gigaphoton introduced a 45-W ArF excimer laser, model GT40A, to semiconductor markets as a light source for 65 nm lithography generation. The GT40A is based on injection lock technology with G-electrode, magnetic bearing and high resolution technologies for high reliability and long lifetime. As a result, GT40A showed the stable performance during the chamber maintenance interval of over 15 billion pulses. In this paper we will report the longterm stability of GT40A.
H. Mizoguchi, T. Inoue, J. Fujimoto, T. Yamazaki, T. Suzuki, T. Matsunaga, S. Sakanishi, M. Kaminishi, Y. Watanabe, T. Ohta, M. Nakane, M. Moriya, T. Nakaike, M. Shinbori, M. Yoshino, T. Kawasuji, H. Nogawa, T. Ito, H. Umeda, S. Tanaka, H. Taniguchi, Y. Sasaki, J. Kinoshita, T. Abe, H. Tanaka, H. Hayashi, K. Miyao, M. Niwano, A. Kurosu, M. Yashiro, H. Nagano, N. Matsui, T. Mimura, K. Kakizaki, M. Goto
KEYWORDS: Molybdenum, Lithography, High power lasers, Optical lithography, 193nm lithography, Control systems, Light sources, Optical components, Oscillators, Laser development
193-nm lithography is moving from the pre-production to the mass production phase and its target node is
shifting from 90 nm to 65 nm. And now the ArF-immersion technology is spotlighted as the enabling technology
for below 45nm node1). 157nm lithography is still important for next generation node below 45 nm as backup
technology2).
Gigaphoton has already released G40A (20W, 0.35pm) in 2001, G41A (20W, 0.30pm)3) in 2002, G42A (20W,
0.25pm)4) in 2003 to the advanced lithography market. On the other hand, since 1998 we have been developing
high power 157nm light source for micro lithography with injection lock technology in research phase5)6). We
have demonstrated a 30W, 0.12pm, @157nm line narrowed light source for microlithography with
"Injection lock technology"1)2). Based on this injection lock technology, we have successfully developed
"GigaTwin", a high power injection lock laser platform for 193nm lithography system. We have already
released a high power ultra narrowed ArF laser "GT40A" (45W, 4000Hz, 11.25mJ, 0.18pm), with the GigaTwin
platform.
New light source technology for ArF lithography under 65nm node is introduced. That is “GigaTwin” platform based on “Injection Lock” technology. The new product named GT40A is 60W (4000Hz, 15mJ), 0.18pm high power ultra narrowed ArF laser. The “Injection Lock” technology provides higher performance and lower CoO. GT40A has enabled the target of more than 60ns pulse duration by natural long pulse and optical pulse stretcher. Combination of “Injection Lock” technology and Gigaphoton’s key technologies; “Higher resolution” technology, “Magnetic bearing” technology and “G-electrode” technology promise durable and reliable performance of GT40A. These technologies enable the target of chamber maintenance interval more than 12 billion pulses. The GT40A will be release into market by 4Q 2004. We introduce latest development data of GT40A, which is developed new high power “Injection Lock” laser platform for VUV/DUV lithography system.
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).
The roadmap of semiconductor fabrication predicts that the semiconductor market will demand 65 nm node devices from 2004/2005. Therefore, an Ultra-Line-Narrowed F2 laser for dioptric projection systems is being developed under the ASET project 'The F2 Laser Lithography Development Project.' The target of this project is to achieve a F2 laser spectral bandwidth below 0.2 pm (FWHM) and an average power of 25W at a repetition rate of 5 kHz. Accurate measurements of the laser spectrum and of the laser wavelength stability are therefore very important. We therefore developed a VUV wavemeter with a Br-lamp to measure the absolute F2 laser wavelength. We obtained 157.631 nm for the main F2 laser transition using the Br-lamp reference lines at 157.4840 nm and 157.6385 nm. We have also developed a VUV high-resolution spectrometer to measure spectral profiles, which was calibrated by 157 nm coherent light source (157CLS). The 157CLS is a very narrow line-width, which can be approximated by delta function. The 157CLS had a line-width of 0.008 pm (Full-Width-At-Half- Maximum, FWHM) and a power of 0.1 mW. The instrument function of the high-resolution spectrometer measured by the 157CLS was 0.10 pm (FWHM). As a result, the deconvolved FWHM of the ultra-line narrowed F2 laser is 0.12 pm, the deconvolved spectral purity containing 95% of the total energy (E95) was less than 0.45 pm.
F2 lasers are the light source of choice for microlithographic tools enabling structures below the 70 nm technology node. Accurate measurements of the spectrum of F2 lasers are therefore very important. We have succeeded in measuring the spectrum of an ultra line narrowed F2 laser using a VUV grating spectrometer calibrated with a 153 nm coherent light source (153CLS). As a first step in the development of a 157 nm coherent light source (157CLS), the less complex 153CLS has been built. Using resonant two-photon processes and four-wave mixing in Xe, this method provided a tunable laser system with high conversion efficiency and a very narrow linewidth, which can be approximated by a (delta) function. The 153CLS included a pulsed, single-mode tunable Ti:sapphire laser (768.0 nm), a third harmonic generation unit (256.0 nm) and an Xe gas cell. The 153CLS had a linewidth of 0.007pm (FWHM) and a power of 0.05mW at 1000 Hz. The VUV grating spectrometer and a Michelson interferometer for F2 lasers have also been developed. The instrument function of the spectrometer has been measured with the 153CLS. Experimental and theoretical instrument functions were in good agreement (FWHM: 0.30pm). The instrument function at 157 nm was therefore estimated to have the theoretical FWHM of 0.31 pm. The spectral linewidth of the line-selected F2 laser has been measured under various laser conditions with the spectrometer as well as with the interferometer. Results show good agreement between both measurements. The spectrum of the ultra line narrowed F2 laser was measured with the VUV grating spectrometer calibrated using the 153CLS. The laser's FWHM of the deconvolved spectrum was 0.29pm. The deconvolved spectral purity containing 95% of the total laser energy is less than 0.84pm.
Recently, we have developed a novel Br lamp for the F2 laser wavelength calibration. In order to examine the validity of this lamp, we measured emission lines of this lamp in 157 nm region and analyzed them. From our result, it has been confirmed that the spectral profile of the 157.6387 nm (2P3/2 - 4P5/2) emission line of Br atom is unchangeable to the parameters of lamp designs and lamp operating conditions. One of the reasons will be shown here. Hence our novel Br lamp is to be the promising candidate for the 157 nm F2 laser wavelength calibration.
Deep UV lithography using ArF excimer laser requires very narrower spectral properties. However, spectrometers that have sufficient resolution to evaluate the ArF excimer laser are commercially not available. High-resolution multi-grating spectrometers for measuring spectral bandwidth at full width at half maximum (FWHM) and spectral purity of ArF excimer lasers are introduced. To achieve high resolution, a special grating arrangement called HEXA (Holographic and Echelle Gratings Expander Arrangement) is designed. A holographic grating and an echelle grating are used so that the input light is expanded and diffracted several times. The resolution of the HEXA spectrometer is more than two million. To evaluate the resolution and the stability of the spectrometer, we measured the instrument function by a coherent light source whose wavelength is same as ArF excimer laser. The experimentally obtained resolution of the spectrometer is 0.09pm or 0.05pm that is selectable. The measured dispersion has a good agreement with the theoretical value. To evaluate the spectral properties of excimer lasers, the instrument function must be very stable. This high-resolution spectrometer enables high quality control of line-narrowed ArF excimer laser mass production.
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.
The design of high-resolution multi-grating spectrometers for measuring the spectral line width at full width at half maximum and the purity of KrF/ArF excimer lasers is outlined. A special configuration of gratings called DEGA is described in detail. DEGA uses two identical echelle gratings with identical angles of incidence. The focal lengths of the imaging mirrors are 1.8m. The output slit image is magnified five times and detected by a back illumination CCD detector array having a very high DUV sensitivity. The theoretical dispersion of the DEGA spectrometer is 1.2pm/mm. The experimentally measured dispersion of 1.2pm/mm is in good agreement with the theoretical value. The measured resolution is 0.11 pm at the KrF excimer laser wavelength. The long-term stability of DEGA has been evaluated and proven to be sufficiently high to use the spectrometer for high quality KrF/ArF excimer laser production.
We have succeeded in the commercialization of the world's 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.
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.
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.
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