The effect of pulse duration of Nd:YAG laser with wavelength of 1.064 μm on the generation of 13.5 nm extreme
ultraviolet (EUV) emission and ions was investigated. It was found that almost constant in-band (2 % bandwidth)
conversion efficiency (CE) is obtained from Sn plasmas irradiated with Nd:YAG laser pulse with durations from 0.13 to
30 ns. It was also noted that Sn ions kinetic energy generated with a 30 ns laser pulse is much less than those with 0.13
and 7 ns laser pulses. The measurement on the narrow-band EUV imaging showed that EUV source size strongly
depends on laser intensity instead of pulse duration and small EUV size is still possible with laser pulse duration as long
as 30 ns. The key reason for the constant CE and the still small EUV source size obtained with long laser pulse duration
comes from the small laser focal spot employed in the present experiment, i.e., 40 μm (FWHM). This research shows
that an efficient and bright EUV source is feasible with a long pulse duration Nd:YAG laser. The lower peak intensity of
EUV emission due to the long pulse duration makes the EUV source more suitable for EUV metrology.
Experimentally observed density profile of CO2 laser-produced Sn plasma was compared with that predicted by one
dimensional hydrodynamic radiation numerical code. Experimental data showed a much smaller corona and a much
shorter shift distance of the critical density from the initial target surface as compared with those predicted by an
isothermal model and the numerical simulation. The possible reason may come from thin localized laser deposition
region, less energy transport into the corona and into the dense region beyond the critical density. This research suggests
that more efforts to understand the fundamental dominating the interaction of CO2 laser with high Z plasma are
necessary to form a more solid foundation for the application of numerical method to the development of the EUVL
source.
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.
A laser produced plasma light source for a small field exposure tool (SFET) has been developed at the EUVA Hiratsuka
R&D center. The light source consists of the following components: 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 an unstable resonator and produces 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 35 m/s. The source has been designed to generate
0.5W in-band power at the intermediate focus (IF) at a collecting solid angle of pi sr. The source includes automatic
control, e.g. jet and plasma position control, and an electrical interface for the exposure tool. The performance of the
source at IF has been evaluated by Canon Inc. This paper explains source performances. Especially, results of IF
parameters like image size, position stability and out of band radiation are presented.
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.
Particle-cluster tin target is presented as the solution of a 100W EUV source for EUVL. Theory for maximizing conversion efficiency of a laser-produced plasma is derived and the theory is experimentally confirmed by using a dispersed SnO2 particles. The EUV intensity 4 times higher than that from a plasma on a solid Sn plate target is observed at the optimized density. The achieved conversion efficiency for dispersed particles is estimated to be as high as 3%/(2π str 2%BW) or higher from the value for a Sn plate of 0.8% measured by using two multilayer mirrors and a calibrated photodiode. Theoretical consideration reveals that larger diameter plasma enables higher EUV power. The particle-cluster can be delivered at multi kHz rep-rate by using water droplet. Experimental confirmation of delivering particles by droplets is also reported.
In order to protect a multilayer mirror from sputtering or ion implantation, high-energy ions ejected from EUV source plasma are to be blocked. We propose use of a laser-produced plasma as an ultra-fast shutter. Ion signal form an ion-source plasma dropped abruptly by two orders of magnitude to a noise level after the shutter plasma generation. The stopping effect for the high-energy ions was observed to reduce as the distance of shutter plasma expansion increases, but the suppression of ions below detection level was observed up to 10 mm. We concluded that reduction of ion signal was caused by in-take of the source plasma flow into the stream of the shutter plasma.
Magnetic field shield for laser produced plasma (LPP) had been investigated. The interaction between expanding LPP and magnetic field is not described by Lorentz force, but, may be described by magneto hydro dynamics. When a magnetic field strength of 0.6T was placed between LPP and a faraday cup, attainment ratio of plasma to a faraday cup was decrease to 20%. The attainment ratio was decreased from 0.4 to 0.25 with varying the distance between the plasma and the magnetic field from 10 mm to 70 mm. And, it was observed that plasma detoured around a magnetic field.
Laser plasma light source using double pulses laser irradiation and through-hole method is proposed as a mass-limited target srouce for extreme UV (EUV) radiation. After minimum necessary material is supplied using the ablation laser from a solid target, only ablated material is irradiated with the heating laser to produce a high-temperature plasma, and EUV radiation is extracted passing through the hole formed in the solid target. Fundamental concept of this scheme, EUV radiation and great reduction of particle debris were experimentally confirmed.
We succeeded in generating a strong narrowband peak at 13.7 nm in a cavity confined Sn plasma. Fraction of the energy within 2% bandwidth at 13.7 nm against the total radiation spectrum was 11.3%. In our experiment, the plasma is generated not on a solid plate but in a cavity as described below. A YAG laser pulse ablates the surface of a concave structure Sn target in order to supply the material for plasma generation. The next laser pulse with 1064nm wavelength heats the ablated material to generate a high temperature plasma. The ablation YAG laser is focused to 600μm diameter with a flux of 10 J/cm2. The heating YAG laser is focused to 100μm diameter at a delay time of 30 ns after the laser ablation. Emission spectra are observed using a grazing incidence Hitachi flat-field grating and a back side illuminated CCD detector. Fraction of the energy at 13.7nm within 2% bandwidth in the whole radiation energy was 11.3%. However, the intensity of the spectrum peak was about 1/10 against the plane Sn target LPP source. When nano (less than 200 nm diameter) particle SnO2 deposited on a 100nm-thick Si3N4 membrane were irradiated, a sharp peak was observed. The intensity of the spectral peak of the nano particle SnO2 target LPP source was as high as that of the plane Sn target LPP source. The EUV energy within 2% bandwidth at around 13.7 nm to the whole radiation energy of the nano particle SnO2 target LPP source was 7.4%.
Debris-free generation of a tin plasma was demonstrated in the cavity-confined configuration. Narrow band emission at 13.7-nm was observed in an emission spectrum of a cavity confined tin plasma. The spectral efficiency was as high as 12% and we found the conversion efficiency could reach 6%/2π str ultimately while lots of works are required to achieve this value. We also confirmed a magnetic field has some effect of stopping a plasma.
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 currently being developed under the ASET project of 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 25 W at a repetition rate of 5 kHz. The energy stability (3-sigma) target is less than 10%. An Oscillator-Amplifier arrangement at 2 kHz was developed as a first step of an Ultra-Line-Narrowed F2 laser system. With this laser system, we did the basic study of the synchronization technology for line narrowing operation using two system arrangements: MOPA (Master Oscillator/Power Amplifier) and Injection Locking. Based on this experience we have developed the 5 kHz system. With the 5 kHz Line-Narrowed Injection Locking system, we have achieved a spectral bandwidth of < 0.2 pm with an output energy of > 5 mJ and an energy pulse to pulse stability of 10%. The feasibility of a 5 kHz Ultra-Line-Narrowed F2 Laser for Dioptric Projection Systems has been demonstrated.
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.
It is predicted that the semiconductor market will demand 70 nm devices from 2004 or 2005. Hence, F2 laser microlithography systems have to be developed according to this time frame. At ASET, 'The F2 Laser Lithography Development Project' started in March 2000, as a 2-year project to fulfill this market requirement. The final target of this project is to achieve a F2 laser spectral bandwidth of 0.2 pm (FWHM) at a repetition rate of 5000 Hz and an average power of 25 W. These specifications meet the demand of dioptric projection system. We have done a feasibility study for a high efficiency line narrowing design to achieve the ultra narrow spectral bandwidth and the high output power. In addition, we have developed an intermediate engineering laser system consisting of an oscillator laser and an amplifier. With this laser system we have performed the line-narrowed operation using two arrangements: Master Oscillator Power Amplifier (MOPA) and Injection Locking. With this Oscillator-Amplifier system and have achieved a spectral bandwidth (convoluted) of FWHM <0.2 pm with both systems: MOPA and Injection Locking. The maximum output energy was >20 mJ for MOPA and >15 mJ for Injection Locked operation.
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