Due to the demand to realize shorter wavelength light sources, extreme ultraviolet (EUV) sources and soft x-ray laser (SXRL) are under development. The development of EUV sources at the wavelength of 13.5 nm started to realize light sources to be used for next generation lithography. Xenon was used at the beginning of development, however, to attain higher conversion efficiency, tin is now used as fuel. As a coherent light source, capillary discharge SXRL is under development. After the demonstration of Ne-like Ar SXRL by using electron collisional excitation scheme, the effort to shorten the wavelength has been made by adopting recombination scheme such as H-like N. Though the challenge has not yet been successful, the source has potential to be used as a SXR source in the water window wavelength region. Current status of EUV and SXR sources based on discharge produced plasma will be given.
High-radiance EUV source is needed for actinic mask inspection applications. LDP source for a lithography application was found to be also able to provide sufficient radiance for mask inspection purpose. Since the plasma size of LDP is properly larger than LPP, not only radiance but also power is suitable for mask inspection applications. Operating condition such as discharge pulse energy, discharge frequency and laser parameter have been tuned to maximize radiance. Introduction of new techniques and several modifications to LDP source have brought radiance level to 180 W/mm2/sr at plasma (or 130 W/mm2/sr as clean-photon radiance). The LDP source is operated at moderate power level in order to ensure sufficient component lifetime and reliability. The first lifetime test done at 10 kHz resulted in 6.5 Gpulse without failure. Debris mitigation system has been successfully installed showing optical transmission as high as 71 %.
For industrial EUV (extreme ultra-violet) lithography applications high power EUV light sources are needed at a central
wavelength of 13.5 nm. Philips Extreme UV GmbH, EUVA and XTREME technologies GmbH have jointly developed
tin DPP (Discharge Produced Plasma) source systems.
This paper focuses in the first part on the results achieved from the Alpha EUV sources in the field. After integration of
power upgrades in the past, now the focus is on reliability and uptime of the systems.
The second part of this paper deals with the Beta SoCoMo that can be used in the first pre-production scanner tools of the
lithography equipment makers. The performance will be shown in terms of power at Intermediate Focus, dose stability
and product reliability but also its reachable collector lifetime, the dominant factor for Cost of Operation.
In the third part of the paper the developments for the high volume manufacturing (HVM) phase are described. The basic
engineering challenges in thermal scaling of the source and in debris mitigation can be proven to be solvable in practice
based on the Beta implementation and related modeling calibrated with these designs. Further efficiency improvements
required for the HVM phase will also be shown based on experiments. The further HVM roadmap can thus be realized as
evolutionary steps from the Beta products.
Discharge-produced plasma (DPP)-based EUV source is being developed at Gotenba Branch of EUVA Hiratsuka R&D Center. A high-repetition-rate high voltage power supply (HVPS) was developed and put into operation on the magnetic pulse compression (MPC)-driven DPP source, enabling 8-kHz operation with 15 J/pulse of maximum charging energy and 0.11 % of stability. SnH4 gas was used as a fuel gas in order to obtain high conversion efficiency. SnH4-fueled Z-pinch source demonstrated EUV power of 700 W/2&pgr;sr within 2 % bandwidth around 13.5 nm. Using a nested grazing-incidence collector, EUV power at the intermediate focus which is defined as an interface to the exposure tool reached 62 W with 3.3 mm2sr of etendue. Tin deposition rate on the collector surface, which is the concern in any tin-fueled EUV sources, was decreased by four orders of magnitude as a result of debris-shield development. Cleaning processes were also developed to enhance total lifetime of the collector. A sequence of intentional deposition and cleaning process for the ruthenium grazing-incidence mirror sample was repeated 13 times. By measuring reflectivity of the mirror, it was confirmed that halogen cleaning process worked very effectively and did not get the mirror damaged after such a long-term cleaning experiment.
Discharge-produced plasma (DPP) based EUV source is being developed at Gotenba Branch of EUVA Hiratsuka R&D Center. Among the several kinds of discharge scheme, Z-pinch is employed in our source. An all-solid-state magnetic pulse compression (MPC) generator is used to create a Z-pinch plasma. Low inductance MPC generator is capable of producing a pulsed current with over 50 kA of peak amplitude and about 100 ns of pulse duration at 7 kHz of pulse repetition frequency. In order to obtain sufficient output radiation power, tin-containing gas is being used as well as xenon. Due to the high spectral efficiency of tin, demonstrated EUV output power reached 645 W/2πsr within 2% bandwidth around 13.5 nm. A novel scheme of fuel gas supply led to as good output energy stability as xenon can achieve. Using a nested grazing-incidence collector, EUV power at intermediate focus point which is defined as an interface to the exposure tool reached 42 W with 3.3 mm2sr of etendue.
Discharge-produced plasma (DPP) based EUV source have been studied and developed at EUVA/Gotenba Branch. Among the several kinds of discharge scheme, a capillary Z-pinch has been employed in our source. An all-solid-state magnetic pulse compression (MPC) generator was used to create a Z-pinch plasma. Low inductance MPC generator provides a pulsed current with about 52 kA of peak amplitude and 120 ns of pulse duration, and allows 7-kHz operation. A water-cooled discharge head was coupled with the MPC generator. In order to evaluate the source performance, electrical energy input to the discharge, EUV radiation power, radiation spatial profile, plasma image and spectra were observed. In-band EUV power into usable solid angle obtained at 7 kHz was 93 W/2%BW. By using nested grazing-incidence collector, EUV power at intermediate focus obtained was 19 W/2%BW.
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.
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.
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.