Hiroshi Someya

Laser-produced-plasma light source for EUV lithography

The status of the next generation lithography laser produced plasma light source development at EUVA is presented. The light source is based on a Xenon jet target and a Nd:YAG driver laser. The laser, having a master oscillator power amplifier (MOPA) configuration, operates at 10 kHz repetition rate and generates an average output power of 1.5 kW. The fwhm pulsewidth is 6 ns. The EUV system currently delivers an average EUV source power of 9.1 W (2% bandwidth, 2π sr) with a conversion efficiency of 0.6 %. Based on the development it is concluded that solid-state Nd:YAG laser technology can be cost efficiently used to produce 10 W level EUV light sources. In order to generate an average power of 115 W for a future extreme ultraviolet (EUV) light source, however, the cost of a Nd:YAG based LPP source will be too high. Therefore RF-CO2 laser technology will be used. The designed CO2 driver laser system has a MOPA configuration. The oscillator has ns-order pulsewidth and the laser system operates at a repetition rate of 100 kHz. Due to its inert cleanliness Xenon droplets will be the target material.

Laser-produced plasma source development for EUV lithography

We are developing a laser produced plasma light source for high volume manufacturing (HVM) EUV lithography. The light source is based on a high power, high repetition rate CO2 laser system, a tin droplet target and a magnetic plasma guiding for collector mirror protection. This approach enables cost-effective high-conversion efficiency and EUV power scaling. The laser system is a master oscillator power amplifier (MOPA) configuration. We have achieved a maximum average laser output power of more than 10 kW at 100 kHz and 20 ns pulse by a single laser beam with good beam quality. EUV in-band power and out-of-band characteristics are measuring with high power CO2 laser and Sn droplet target configuration. This light source is scalable to more than 200 W EUV in-band power based on a 20-kW CO2 laser. Collector mirror life can be extended by using droplet target and magnetic plasma guiding. Effectiveness of the magnetic plasma guiding is examined by monitoring the motion of fast Sn ion in a large vacuum chamber. The ion flux from a Sn plasma was confined along the magnetic axis with a maximum magnetic flux density of 2 T.

Performance of a 10-kHz laser-produced-plasma light source for EUV lithography

The main technological challenge of a future extreme ultraviolet (EUV) light source is the required average power of 115W at the intermediate focus. High repetition rate laser produced plasma (LPP) sources are very promising to face this challenge. We report the current status of the laser produced light source system we started to develop in 2002. The system consists of the following main components: The plasma target is a liquid xenon jet with a maximum diameter of 50 micrometer and a velocity of more than 30 m/s. A Nd:YAG laser oscillating at 1064 nm produces the plasma. The laser is a master oscillator power amplifier (MOPA) configuration with a maximum repetition rate of 10 kHz and an average power of 1kW. The EUV system currently delivers an average EUV in-band power of 4 W (2% bandwidth, 2π sr) having a stability of 0.54 % (1σ, 50-pulse moving average). In order to evaluate a further increase of the repetition rate, xenon jet characteristics and EUV plasma images have been investigated at 10 kHz. In addition, a conversion efficiency of 0.67% (2% bw, 2π sr) has been obtained at low repetition rate operation. This paper presents the progress of our LPP light source development.

Development of liquid-jet laser-produced plasma light source for EUV lithography

The Extreme UV Lithography System Development Association (EUVA) was established in Japan in May 2002 and is supported by the Ministry of Economy, Trade and Industry (METI). EUVA started the light soruce development in September 2002. This development is done by the assocaition members Gigaphoton, Ushio, Komatsu, Canon, Nikon, the National Institute of Advanced Industrial Sciecne and Technology (AIST) and several Japanese universities. The target of the four-year project is the development of a EUV light source with 10W clean focus point power. For the end of the fiscal year 2003 the development of a 4W EUV light source (clean focus point power) is planned. Both, Laser-Produced-Plasma (LPP) and Discharge-Produced-Plasma (DPP) EUV light sources are investigated at first. Our group at the EUVA Hiratsuka R&D Center is working on LPP sources. We are currently focusing on the development of a driver laser and a liquid Xenon plasma target. The laser is a Nd:YAG MOPA (Master Oscillator and Power Amplifier) system oscillating at 1064 nm. Average power, repetition rate and pulse duration of the laser system are 500 Watt, 10 kHa and 30nsec, respectively. The Xenon liquefication system operates at a maximum pressure of 5MPa and a temperature range between 160 K and 190 K. The pressure inside the vacuum chamber is below 0.1Pa during system operation. This paper presents the current status of the EUV system component development as well as first experimental results of generated EUV radiation.

Development of CO 2 laser produced Xe plasma EUV light source for microlithography

A CO2 laser driven Xe droplet plasma is presented as a light source for EUV lithography. A short-pulse TEA CO2 master oscillator power amplifier system and a pre-pulse Nd:YAG laser were used for initial experiment with 0.6% of CE from a Xe jet. A target technology is developed for high average power experiments based on a Xe droplet at 100kHz. Magnetic field ion mitigation is shown to work well in the pre-pulsed plasma combined with a CO2 laser main pulse. This result is very promising with respect to collector mirror lifetime extension by magnetic field mitigation. A master oscillator power amplifier (MOPA) CO2 laser system is under development with a few kW and 100 kHz repetition rate with less than 15ns laser pulse width using a waveguide Q-switched CO2 laser oscillator and RF-excited fast axial flow CO2 laser amplifiers.

Design of high average power clean EUV light source based on laser produced Xenon plasma

Important design factors are evaluated for a high average power, clean EUV light source by laser produced plasma. The basic requirements are high average power, high stability, and long lifetime, and these are closely relating with absorption loss by xenon, repetition rate, and fast ion generation. These subjects are evaluated based on experimental data and analytical model of a laser produced xenon plasma.

KrF laser-driven xenon plasma light source of a small-field exposure tool

A small field exposure tool (SFET) is currently being built in Japan by the Extreme Ultraviolet Lithography System Development Association (EUVA) and Canon Inc. The laser plasma light source of SFET has been developed at the EUVA Hiratsuka R&D center. The drive laser of the xenon plasma source is a short-pulse, high-power KrF laser, that has been developed in cooperation with Gigaphoton Inc. and Komatsu Ltd. The laser has a maximum output power of 580W at 4kHz repetition rate. The xenon target is a 50 micrometer diameter liquid jet with a speed of about 30 m/s. The source has been designed to generate 0.5W in-band power at the intermediate focus at a collecting solid angle of pi sr. The set-up of the source at the Hiratsuka R&D center has been completed and the source is now being evaluated.

EUV emission of solid targets irradiated by femto- and picosecond laser pulses

Various solid materials have been irradiated with laser intensities ranging from 1011 to 1016 W/cm2 and the plasma emission has been measured between 7 nm and 18 nm. A chirped pulse amplified Ti:Sapphire laser oscillating at 790 nm with either 100 fs or 300 ps pulse duration and a Nd:YAG laser oscillating at 1064 nm with 10 ns pulse duration (fwhm) have been used. Tin, aluminum and copper have been chosen as targets. It has been found that the plasma emission was strongest for the 300 ps laser pulse irradiation. This might be due to the additional laser plasma heating during plasma formation.

Emission spectra of laser-produced plasmas for EUV and soft x-ray sources

The plasma emission of tin, aluminum and cupper targets irradiated with laser intensities ranging from 1011 to 1016 W/cm2 has been measured beween 7nm and 18 nm. A chirped pulse amplified Ti:Sapphire laser oscillating at 790- nm with either 100 fs or 300 ps pulse duration and a Nd:YAG laser oscillating at 1064 nm with 10 ns pulse duration (fwhm) have been used. The observed plasma emission was strongest for the 300 ps laser pulse irradiation, which might be due to the additional laser plasma heating during plasma formation.

Measurements of energy distribution functions of xenon ions from laser-produced plasmas for lithography

The collector mirror lifetime of a future extreme ultraviolet lithography light source system is an important development issue. Beside vacuum cleanliness and heat load, fast ions are especially critical in case of laser-produced plasmas causing quick degradation of the multilayer structure of near normal incidence collector mirrors. We are currently developing a light source system based on a laser-produced plasma for next generation lithography. The plasma target is a liquid xenon jet. Energy distributions of fast xenon ions from the laser-produced plasma have been measured by time-of-flight (TOF) experiments. Two low repetition rate Nd:YAG lasers at 1064 nm with pulse lengths of 8 ns and 150 ps have been used for plasma generation and mean ion energies of 3 keV and 7 keV have been measured, respectively. In addition, the effects of fast ions on Mo/Si multilayer mirrors have been studied using a Xe ion gun. Ion sputtering of the multilayer structure is the main damage mechanism but boundary layer mixing and increased surface roughness are also observed.