The 1st generation Laser-Produced Plasma source system "ETS" device for EUV lithography is under development. We
report latest status of the device which consists of the original concepts (1) CO2 laser driven Sn plasma, (2) Hybrid CO2
laser system that is combination of high speed (>100kHz) short pulse oscillator and industrial cw-CO2, (3) Magnetic
mitigation, and (4) Double pulse EUV plasma creation. Maximum burst on time power is 69W (100kHz, 0.7 mJ EUV
power @ intermediate focus), laser-EUV conversion efficiency is 2.3%, duty cycle is 20% at maximum. Continuous
operation time is so far up to 3 hours. Debris is efficiently suppressed by pre-pulse plasma formation and magnetic field
mitigation system. Long-term performance is now under investigation. Also future plan is updated.
We evaluated basic characteristics of energetic plasma ions and neutrals, and of low-energy fragments (e.g. evaporated
material and liquid micro-droplets) from a Tin (Sn) plasma produced by a CO2 (10.6 m) or Nd:YAG (1064 nm) laser.
Experiments were performed with free-standing liquid droplet, semi-fixed liquid droplet and fixed solid droplet targets.
Characteristics of energetic plasma ions, neutrals and fragments were measured by Faraday Cups, laser-induced
fluorescence (LIF) imaging and shadowgraph imaging, respectively. The Sn ions were emitted towards the laser incident
direction with a velocity of 10 ~ 100 km/s (kinetic energy of 0.06 ~ 6 keV) and the fragments (the majority of the target
material) ejected in the same direction as laser pulse at a velocity of 10 ~ 500m/s. The neutrals were emitted in all
directions from the target with a velocity of 5 ~ 40 km/s (kinetic energy of 0.015 ~ 1 keV).
We are developing a CO2 laser driven Tin plasma EUV source for HVM EUVL. This approach enables cost-effective EUV power scaling by high-conversion efficiency and full recovery of Tin fuel. The RF-excited, multi 10 kW average power pulsed CO2 laser system is a MOPA (master oscillator power amplifier) configuration and operates at 100 kHz with 20 ns pulse width. The EUV light source is scalable to in-band 200 W IF power with a single 20-kW CO2 laser beam. EUV chamber is kept uncontaminated by using a small size droplet target and effective Tin exhaust by magnetic plasma guiding. Characterization of the plasma flow in uniform magnetic field was studied by monitoring the motion of Tin plasma stream in a large vacuum chamber, depending on the magnetic flux up to 2 T. Topics relevant for HVM source is reported on continuous operation and Tin vapor evacuation.
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 (10.6μm) system, a tin (Sn) target and a magnetic
ion guiding for Sn treatment. We evaluated the characteristics of Sn debris generated by a CO2 laser produced plasma.
Experiments were performed with bulk Sn-plate targets and Mo/Si multilayer mirror samples were used for debris
analysis. We observed very thin and uniform Sn layers of nano/sub-nano size debris particles. The layer deposition rate
at 120mm from the plasma is, without magnetic field, about 30nm per million shots. The fast Sn ion flux was measured
with Faraday cups and the signal decreased by more than 3 orders of magnitude on application of a magnetic field of 1T.
The Sn deposition on the Mo/Si multilayer mirror decreased in small magnetic field space by a factor of 5. In a large
magnetic field space, the effectiveness of the magnetic guiding of Sn ions is examined by monitoring the fast Sn ions.
The ion flux from a Sn plasma was confined along the magnetic axis with a maximum magnetic field of 2T.
We evaluated the characteristics of Sn debris generated by a CO2 laser (10.6μm) produced plasma. Experiments were
performed with bulk Sn-plate targets and Mo/Si multilayer mirror samples were used for debris analysis. We observed
very thin and uniform Sn layers of nano/sub-nano size debris particles. The layer deposition rate at 120mm from the
plasma is, without magnetic field, about 30nm per million shots. The fundamental magnetic field effect has been
confirmed experimentally. The fast Sn ion flux was measured with Faraday cups and the signal decreased by more than 3
orders of magnitude applying a magnetic field of 1T. The Sn deposition on the Mo/Si multilayer mirror decreased in this
case by a factor of 4. The contribution of the remaining neutral Sn particles is under study in order to decrease the
deposition rate.
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 target and a magnetic ion guiding for
tin treatment. The laser system is a master oscillator power amplifier (MOPA) configuration. We have achieved an
average laser output power of 10 kW at 100 kHz by a single laser beam with good beam quality. EUV in-band power
equivalent to 60 W at intermediate focus was produced by irradiating a tin rotating plate with 6 kW laser power. 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 ion guiding. Effectiveness of the magnetic ion guiding is examined by
monitoring the motion of fast Sn ion in a large vacuum chamber with a maximum magnetic flux density of 2 T.
We are developing a laser produced plasma light source for high volume manufacturing (HVM) EUV lithography. The
light source is based on a short pulse, high power, high repetition rate CO2 master oscillator power amplifier (MOPA)
laser system and a Tin droplet target. A maximum conversion efficiency of 4.5% was measured for a CO2 laser driven Sn
plasma having a narrow spectrum at 13.5 nm. In addition, low debris generation was observed. The CO2 MOPA laser
system is based on commercial high power cw CO2 lasers. We have achieved an average laser power of 7 kW at 100 kHz
by a single laser beam with good beam quality. In a first step, a 50-W light source is under development. Based on a 10-kW CO2 laser, this light source is scalable to more than 100 W EUV in-band power.
We evaluated Sn debris generated from a CO2 laser (10.um) and a Nd:YAG laser (1064nm) plasma. Experiments were
performed with bulk Sn-plates (t=1mm) and freestanding Sn-foils (t=15um). Quartz Crystal Microbalances (QCM) were
used for debris analysis. We observed a drastically lower deposition for the CO2 laser driven plasma compared with the
Nd:YAG laser plasma. In addition, several Sn coated targets with different Sn thickness were investigated for the CO2
drive laser with respect to the generated plasma debris. In general, a 100nm Sn coated glass target generated more debris
than the solid Sn target. Especially, we observed for the Sn-plate target that the deposition rate is smaller than the erosion
(sputter) rate caused by the plasma ions.
We develop a laser produced plasma light source for high volume manufacturing (HVM) EUV lithography. The light
source is based on a short pulse, high power, high repetition rate CO2 master oscillator power amplifier (MOPA) laser
system and a Tin droplet target. A maximum conversion efficiency of 4.5% was measured for a CO2 laser driven Sn
plasma having a narrow spectrum at 13.5 nm. In addition, low debris generation was observed. The CO2 MOPA laser
system is based on commercial high power cw CO2 lasers. We achieve an average laser power of 3 kW at 100 kHz with a
single laser beam that has very good beam quality. In a first step, a 50-W light source is developing. Based on a 10-kW
CO2 laser this light source is scalable to more than 100 W EUV in-band power.
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.
A CO2 laser driven Xe jet plasma is presented as light source system for EUV lithography. A short-pulse TEA C02 master oscillator power amplifier system and a pre-pulse Nd:YAG laser were used for plasma generation. The dependence of EUV plasma parameters, e.g. conversion efficiency, plasma image and in-band and out-of-band spectra, on the delay time between the pre-pulse and the main pulse laser was investigated. A maximum conversion efficiency of 0.6 % was obtained at a delay time of about 200 ns. In addition, characteristics of fast ions were measured by the time-of-flight method. The peak energy of the fast ion energy distribution decreased significantly at delay times larger than 200 ns. This result is very promising with respect to collector mirror lifetime extension by magnetic field mitigation.
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.
Condenser erosion caused by high-energy ions is a current issue in EUV sources. Measurements of the charge and energy distributions of Xe ions by EUVA revealed that energetic, kiloelectronvolt-order ions were formed in Xe-laser-produced plasma (LPP). The charge distribution shows a peak for doubly charged ions, and the number of ions with n charges monotonically decreases as n increases. Since highly charged ions around Xe10+ are probably formed in optimized EUV plasma, the observed charge distribution strongly suggests that charge transfer reactions occur in the LPP chamber. If that is true, the reactions will produce high-energy neutrals. In this study, the rate equations for charge transfer reactions were solved numerically; and the change in charge state distribution over time was calculated. The initial charge distribution was assumed to have a peak for Xe10+, based on the plasma model. The dependence of charge transfer cross section was taken to be nb, where n is the number of charges and b was set near unity, based on the model. The calculated charge distribution agreed well with the experimental data. The calculations predict that charge transfer reactions produce fast neutrals, the number of which is of the same order or larger than that of charged ions.
Fast ions from laser-produced EUV plasma are expected to significantly damage the collector mirror, which is located near the plasma in a EUV light source. Ion sputtering of the multilayer structure may be the main damage mechanism but layer boundary mixing and surface roughness increase are also observed from a Xe plasma exposure experiment. The magnetic field ion mitigation technology was evaluated in order to extend the collector mirror lifetime. A coil pair that produces a maximum static magnetic field of 0.6 T on the coil axis was used for magnetic confinement of ions. Liquid Xe jets of 10 to 30 micron mater in diameter were used as a plasma target. Spatial distributions and energy distributions of ions were measured with Faraday cups and time-of-flight measurements respectively. The effectiveness of the magnetic field ion mitigation was evaluated by measuring the erosion rate with a quartz crystal microbalance. A significant decrease of the Faraday cup signal was monitored by applying a magnetic field of 0.6 T. Though target size dependence on magnetic field effectiveness was observed, measured erosion rate was reduced to less than 10% by applying 0.6-T magnetic field in the case of 10-micron mater Xe jet and 300-mJ Nd:YAG laser irradiation.
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 plasma light source system under development at EUVA. The system consists of the following main components: The plasma target is a liquid xenon jet with a maxium diameter of 50 micrometer and a velocity of more than 35m/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 1 kW. 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 0.74% (2% bw, 2π sr) has been obtained at low repetition rate operation. This paper presents the progress of our LPP light source development.
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.
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.
Collector mirror lifetime evaluation and damage prevention are important technical challenge for the EUV light source
development. High-energy xenon ions emitted from laser-produced EUV plasmas are expected to considerably damage
the collector mirror of the light source. Related to future collector mirror lifetime considerations, fast ions from the laserproduced
plasma have been characterized by time-of -flight (TOF) measurements. Using a low repetition rate 8-ns, 100-
mJ Nd:YAG laser, Xe+ to Xe6+ ions were observed with Xe2+ being the main charge state. 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 layer boundary mixing and surface roughness increase are also observed. A magnetic
confinement scheme is evaluated for ion mitigation.
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.
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.
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.
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.
The Association of Super-Advanced Electronics Technologies (ASET) started The F2 Laser Lithography Development Project in March 2000, to clarify solutions of base F2 lithography technologies. In this project, we are developing an ultra line-narrowed F2 laser light source for exposure tools tat are employing dioptric projection optics. We have developed an intermediate engineering injection- locking laser system that has an oscillator laser and an amplifier to study the feasibility of an ultra line-narrowed F2 laser. A spectral bandwidth of <0.2pm (FWHM) at a repetition rate of 1000Hz and an average power of 14W has been achieved with this laser system. The laser output performance dependence on the relative delay between oscillator laser and amplifier is also measured.
Highly narrowed Argon Fluoride excimer laser for practical refractive exposure system with high NA and wide field size lenses is developed. The laser realizes 0.6 W at 400 Hz. The spectral bandwidth is less than 0.75 pm, the stability of central wavelength is within +/- 0.25 pm and the concentration of energy within 3- pm band is more than 95%. The gas lifetime is more than 1 X 107 pulses without gas purifier. By the one gas life performance test and the short term performance test, we confirm this laser is useful for the development of microlithography process.
New KrF excimer laser for microlithography KLES-G7 with a new simple solid state pulsed power circuit (SPC) is developed. This SPC has several advantages such as less maintenance cost and the higher reliability. The laser realizes 7.5W with 0.8 bandwidth, 600 Hz, 10mJ. The performance and the stability of the laser is demonstrated. The maintenance interval of the SPC is more than 10 X 109 pulse. The KLES-G7 reduces 20 percent of the photon cost compared with the old model. It will accelerate the mass production of after 64Mbit DRAM.
A feasibility study of ArF excimer laser as a light source for subquarter micron design rule lithography is presented. Partially narrowed KLES-G1A ArF laser produces 57-pm (FWHM) bandwidth pulses with an average power of 5.1 W. Narrow-band operated KLES-G1A generated 7.2- pm (FWHM) pulses with 1.4 W. Further high output power with narrow-band spectrum was achieved by using injection-locking technique. The injection-locked ArF laser system generated 0.8-pm (FWHM) bandwidth pulses with an average power of 250 W. We also point out some problems appeared in the laser operation.
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