Takeshi Ohta

LPP-EUV light source development for high volume manufacturing lithography

Since 2002, we have been developing a CO2-Sn-LPP EUV light source, the most promising solution as the 13.5 nm high power (>200 W) light source for HVM EUV lithography. Because of its high efficiency, power scalability and spatial freedom around plasma, we believe that the CO2-Sn-LPP scheme is the most feasible candidate as the light source for EUVL. By now, our group has proposed several unique original technologies such as CO2 laser driven Sn plasma generation, double laser pulse shooting for higher Sn ionization rate and higher CE, Sn debris mitigation with a magnetic field, and a hybrid CO2 laser system that is a combination of a short pulse oscillator and commercial cw-CO2 amplifiers. The theoretical and experimental data have clearly demonstrated the advantage of combining a laser beam at a wavelength of the CO2 laser system with Sn plasma to achieve high CE from driver laser pulse energy to EUV in-band energy. Combination of CO2 laser power and droplet generator improvements on new EUV chamber (Proto-2) enables stable EUV emission. EUV burst operation data shows stable average 10.2W(clean power @ I/F) EUV emission and maximum 20.3W(clean power @ I/F) was demonstrated. For future HVM the maximum of 4.7% CE with a 20 μm droplet are demonstrated by ps pre-pulse LPP. Also reported 40kW CO2 laser development project cooperate with Mitsubishi electric.

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.

Multiline short-pulse solid-state seeded carbon dioxide laser for extreme ultraviolet employing multipass radio frequency excited slab amplifier

In this Letter we describe in more detail a solid-state seeded, nanosecond pulse, multiline CO(2) oscillator designed and built for the extreme ultraviolet (EUV) laser-produced-plasma (LPP) source. Our oscillator featured quantum cascade laser seeders, a diffraction-type seed beam combiner, and a radio-frequency-discharge-excited, diffusion-cooled, slab-waveguide CO(2) gain cell in a compact multipass regenerative amplifier configuration. The oscillator generated pulses of exceptional stability in terms of envelope, energy, and spectrum. Excellent stability of output was achieved without any additional techniques. The output spectrum consisted of two laser lines of a 00(0)1-10(0)0 band of a CO(2) molecule, P20 and P22, with a target of four lines P18-P24. The pulse duration was electronically adjustable between 11 and 35 ns at a repetition frequency from a few hertz to hundreds of kilohertz. Electronic adjustment of the pulse duration was achieved by relative timing offsets of individual seeders, opening an avenue to a range of on-line adjustments of pulse shape and spectral content timing. The jitter-tolerant operation allows for easy synchronization with an external event, such as a droplet target in an EUV LPP source. A resistance to parasitic seeding of more than 40 dB was recorded. The oscillator produced up to 20 W of average output power at a repetition rate of 100 kHz in a near-diffraction-limited beam of M(2)<1.3 and a pointing stability below 50 μrad.

High-power and high-energy stability injection lock laser light source for double exposure or double patterning ArF immersion lithography

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.

Development of the reliable high power pulsed carbon dioxide laser system for LPP EUV light source

Laser Produced Plasma (LPP) Extreme Ultra Violet (EUV) light source is expected to be used for next generation lithography. To realize such performance for industrial use, the main driver laser is one of the key components. Our source uses a high power pulsed carbon dioxide (CO2) laser as a plasma driver. A master oscillator and a power amplifier (MOPA) system based on a new configuration of an RF-excited CO2 laser is the key to high efficiency. And multiline amplification of CO2 laser is efficient to increase the extraction efficiency in the case of short pulse amplification like this amplification. Numerical result shows the amplification enhancement as 1.3 times higher than the single line amplification. This report shows its initial performance. Multiline configuration is applied to the master oscillator and the efficiency of multiline amplification is verified in our experimental amplifier system. We have achieved 10% energy extraction improvement using 2 lines (P20+P22) as compared to single line (P20).

Sub-hundred Watt operation demonstration of HVM LPP-EUV source

Since 2002, we have been developing a CO2-Sn-LPP EUV light source, the most promising solution as the 13.5 nm high power (>200 W) light source for HVM EUV lithography. Because of its high efficiency, power scalability and spatial freedom around plasma. Our group has proposed several unique original technologies; 1) CO2 laser driven Sn plasma generation, 2) Double laser pulse shooting for higher Sn ionization rate and higher CE. 3) Sn debris mitigation with a magnetic field, 4) Hybrid CO2 laser system that is scalable with a combination of a short pulse oscillator and commercial cw-CO2 amplifiers. 5) High efficient out of band light reduction with grating structured C1 mirror. In past paper we demonstrated in small size (2Hz) experimental device, this experiment shoed the advantage of combining a laser beam at a wavelength of the CO2 laser system with Sn plasma to achieve high CE>4.7% (in maximum) from driver laser pulse energy to EUV in-band energy 1). In this paper we report the further updated results from last paper. (1) 20um droplets at 100kHz operation was successfully ejected by downsized nozzle and demonstrated dramatical improvement of debris on the collector mirror. We have been developing extension of high CE operation condition at 20kHz range, We have reported component technology progress of EUV light source system. (2)New generation collector mirror with IR reduction technology is equipped in mirror maker. (3)20kW CO2 laser amplifier system is demonstrated cooperate with Mitsubishi electric. (4) We develop new Proto #2 EUV LPP source system and demonstrated 200W EUV plasma power (43W EUV clean power at I/F ) at 100kHz operation was confirmed. (5) High conversion efficiency (CE) of 3.9% at 20kHz operation was confirmed in using pico-second pre-pulse laser. (6)Improvement of CO2 laser power from 8kW to 12kW is now on going by installation of new pre-amplifier. (7)Power-up scenario of HVM source is reported, target shipment of first customer beta LPP light source unit is 2015.

Spectral characteristics of quantum-cascade laser operating at 10.6 μm wavelength for a seed application in laser-produced-plasma extreme UV source

In this Letter, we investigate, for the first time to our knowledge, the spectral properties of a quantum-cascade laser (QCL) from a point of view of a new application as a laser seeder for a nanosecond-pulse high-repetition frequency CO(2) laser operating at 10.6 μm wavelength. The motivation for this work is a renewed interest in such a pulse format and wavelength driven by a development of extreme UV (EUV) laser-produced-plasma (LPP) sources. These sources use pulsed multikilowatt CO(2) lasers to drive the EUV-emitting plasmas. Basic spectral performance characteristics of a custom-made QCL chip are measured, such as tuning range and chirp rate. The QCL is shown to have all essential qualities of a robust seed source for a high-repetition nanosecond-pulsed CO(2) laser required by EUV LPP sources.

Wavefront measurement of single-mode quantum cascade laser beam for seed application in laser-produced plasma extreme ultraviolet system

Quantum cascade laser (QCL) is a very attractive seed source for a multikilowatt pulsed CO2 lasers applied for driving extreme ultraviolet emitting plasmas. In this Letter, we investigate output beam properties of a QCL designed to address P18 and P20 lines of 10.6 micron band of CO2 molecule. In particular, output beam quality and stability are investigated for the first time. A well-defined linear polarization and a single-mode operation enabled a use of phase retrieval method for full description of QCL output beam. A direct, multi-image numerical phase retrieval technique was developed and successfully applied to the measured intensity patterns of a QCL beam. Very good agreement between the measured and reconstructed beam profiles was observed at distances ranging from QCL aperture to infinity, proving a good understanding of the beam propagation. The results also confirm a high spatial coherence and high stability of the beam parameters, the features expected from an excellent seed source.

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.