High-throughput actinic mask inspection tools are needed as EUVL begins to enter into volume production phase. One of the key technologies to realize such inspection tools is a high-radiance EUV source of which radiance is supposed to be as high as 100 W/mm2/sr. Ushio is developing laser-assisted discharge-produced plasma (LDP) sources. Ushio’s LDP source is able to provide sufficient radiance as well as cleanliness, stability and reliability. Radiance behind the debris mitigation system was confirmed to be 120 W/mm2/sr at 9 kHz and peak radiance at the plasma was increased to over 200 W/mm2/sr in the recent development which supports high-throughput, high-precision mask inspection in the current and future technology nodes. One of the unique features of Ushio’s LDP source is cleanliness. Cleanliness evaluation using both grazing-incidence Ru mirrors and normal-incidence Mo/Si mirrors showed no considerable damage to the mirrors other than smooth sputtering of the surface at the pace of a few nm per Gpulse. In order to prove the system reliability, several long-term tests were performed. Data recorded during the tests was analyzed to assess two-dimensional radiance stability. In addition, several operating parameters were monitored to figure out which contributes to the radiance stability.
The latest model that features a large opening angle was recently developed so that the tool can utilize a large number of debris-free photons behind the debris shield. The model was designed both for beam line application and high-throughput mask inspection application. At the time of publication, the first product is supposed to be in use at the customer site.
High-throughput and -resolution actinic mask inspection tools are needed as EUVL begins to enter into volume production phase. To realize such inspection tools, a high-radiance EUV source is necessary. Ushio’s laser-assisted discharge-produced plasma (LDP) source is able to meet industry’s requirements in radiance, cleanliness, stability and reliability. Ushio’s LDP source has shown the peak radiance at plasma of 180 W/mm2/sr and the area-averaged radiance in a 200-μm-diameter circle behind the debris mitigation system of 120 W/mm2/sr. A new version of the debris mitigation system is in testing phase. Its optical transmission was confirmed to be 73 %, which is 4 % lower than that of the previous version and therefore will be improved. Cleanliness of the system is evaluated by exposing Ru mirrors placed behind the debris mitigation system. Ru sputter rate was proven to be sufficiently low as 3~5 nm/Gpulse at 7 kHz, whereas frequency-dependent sputter rate was 1~3 nm/Gpulse at 5~9 kHz as previously reported. Sn deposition remained very low (< 0.05 nm) and did not grow over time. A new technique to suppress debris was tested and preliminary results were promising. Time-of-flight signal of fast ions was completely suppressed and Ru sputter rate of exposed mirrors at 3 kHz was approximately 1.3 nm/Gpulse, whereas the conventional mitigation system (new version) resulted in Ru sputter rate of 0.7 nm/Gpulse. This new technique also allows increasing the radiance efficiency by 30 %. Stability tests were done at several different discharge frequencies. Pulse energy stability was approximately 10 %. Dose energy stability dropped from approximately 2 % to 0.1 % when feedback control was activated. EUV emission position stability was studied at 3 kHz. Deviation of the plasma center of gravity was 6 μm, which is 3 % of plasma diameter and therefore considered to be negligible. Reliability tests were performed on both R and D and prototype machines and up to 200 hours of non-interrupted operation was demonstrated.
Actinic mask inspection manufactures are currently searching for high-radiance EUV sources for their tools. LDP source, which was previously used for lithography purposes, was found to be a good candidate as it can provide sufficient power and radiance. Introduction of new techniques, modified modules and fine tuning of operational conditions (discharge pulse energy, discharge frequency, laser) has brought radiance level to 180 W/mm2/sr at plasma or 145 W/mm2/sr as clean-photon. The source has been modified in such a way to improve modules reliability, lifetime and radiance stability even though there is still a room for further improvement. Size of the source system is much smaller than that of the lithography source. A debris mitigation system has been tested. Optical transmission was improved to 77 % and several 8-nm-thick Ru samples were exposed to evaluate contamination and erosion of optics. Preliminary results show low sputter and deposition rates, which supports sufficiently long lifetime of the optics.
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 %.
A laser-triggered DPP source is being developed and showing considerable progress toward HVM. Performance, in
terms of power and lifetime, of DPP sources has been proven by long-term usage in lithography development fields.
Since high-performance debris-mitigation tools are used in DPP sources, collector lifetime is not an issue. However, it is
worth developing the technology to enhance overall lifetime of the collector module. In order to suppress both neutral
and ionic debris, two technologies, which can be simultaneously used in a DPP source, have been developed. First, a
discharge ignition by using two lasers was developed. It was able to reduce the amount and energy of fast ions which
could sputter a collector by a factor of 5. In addition to fast ion reduction, CE enhancement of 60 % was obtained.
Second, an active control of liquid tin layer, which acts as a fuel material, electrode protection and cooling medium,
could reduce particle debris and lower the load of a debris-mitigation tool. Implementing these technologies is
considered to provide enhancement of the lifetime of the collector module and support HVM readiness.
Debris-mitigation tools (DMTs) have been used in DPP sources and the performance has been well proven in alpha
sources. In beta and HVM sources, requirement to the DMT is increasing to fulfill the power and lifetime requirements
simultaneously. In order to bring DPP technology into HVM level, a high-performance DMT has been developed. It has
high mitigation performance for both neutral and ionic debris, large collection angle of the collector having high optical
transmission, and withstand large thermal input from the discharge source head. Experiments were carried out using
mirror samples and proved sufficient performance with which no sputtering and deposition were observed.
As the traditional techniques used in optical photolithography at 193 nm are running out of steam and are becoming
prohibitively expensive, a new cost-effective, high power EUV (extreme ultra-violet) light source is needed to enable
high volume manufacturing (HVM) of ever shrinking semiconductor devices. XTREME technologies GmbH and EUVA
have jointly developed tin based LDP (Laser assisted Discharge Plasma) source systems during the last two years for the
integration of such sources into scanners of the latest and future generations. The goals of the consortium are 1) to solve
the wavelength gap - the growing gap between the printed critical dimensions (CD) driven by Moore's Law and the
printing capability of lithographic exposure tools constrained by the wavelength of the light source - and 2) to enable the
timely availability of EUV light sources for high volume manufacturing.
A first Beta EUV Source Collector Module (SoCoMo) containing a tin based laser assisted discharge plasma source is in
operation at XTREME technologies since September 2009. Alongside the power increase, the main focus of work
emphasizes on the improvement of uptime and reliability of the system leveraging years of experience with the Alpha
sources. Over the past period, a cumulated EUV dose of several hundreds of Mega Joules of EUV light has been
generated at the intermediate focus, capable to expose more than a hundred thousand wafers with the right dose stability
to create well-yielding transistors. During the last months, the entire system achieved an uptime - calculated according to
the SEMI standards - of up to 80 %. This new SoCoMo has been successfully integrated and tested with a pre-production
scanner and is now ready for first wafer exposures at a customer's site. In this paper we will emphasize what our
innovative concept is against old type of Xe DPP and we will present the recent status of this system like power level,
uptime and lifetime of components as well.
In the second part of the paper the EUV source developments for the HVM phase are described. The basic engineering
challenges are thermal scaling of the source and debris mitigation. Feasibility of the performance can be demonstrated by
experimental results after the implementation into the beta system. The feasibility of further efficiency improvement,
required for the HVM phase, will also be shown. The objectives of the HVM roadmap will be achieved through
evolutionary steps from the current Beta products.
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.
Two projects are being conducted in EUVA under the support of NEDO and member companies; private project and national project. The private project is responsible for power improvement of a source module targeting realization of 115-W prototype. The national project covers wide area of remaining issues on a collector module to achieve sufficient reliability. In the private project, a laser-ablation-discharge-produced plasma (LADPP) is being researched as a candidate of high-power EUV source. LADPP has fascinating properties such as long lifetime, high collection efficiency, and high thermal input. More than 15 % of collection efficiency could be obtained with LADPP because of its small plasma size. Pulse repetition frequency has reached 20 kHz and 580 W/2πsr were achieved so far. In order to increase conversion efficiency (CE), detailed diagnostics of LADPP were carried out. Especially, dependence of CE on laser pulse duration is derived from the experiment. As a result, dynamics of LADPP was understood and solution to increase CE and improve frequency scalability was understood. A fundamental experiment predicted that CE can be increased 60 %.
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.
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 17 kA of peak amplitude and 350 ns of pulse duration, and allows 2-kHz continuous 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, pinhole image and spectra were observed. 54.4 W/2%BW of 13.5-nm EUV output was achieved at 2-kHz operation. Through the radiation profile measurement and pinhole-camera observation, spatial image of EUV radiation was understood.
An EUV radiation source development with discharge-produced plasma (DPP) has been started in Gotenba branch of EUVA Hiratsuka R&D center. For the early stage of the development, fundamental characteristics of DPP including current, voltage, EUV energy and spectrum in EUV region were studied. A capillary of which the inner diameter was 2.3 mm, and Xe gas were used as a source to be expected in-band EUV radiation from magnetically-compressed Z-pinch plasma. An all-solid-state magnetic pulse compression generator was employed, which can deliver the current of 14 kA into the capillary load with the rise time of approximately 500 ns. In-band EUV energy and spectroscopic measurements were carried out. It was found that the in-band EUV energy increased with increasing the current amplitude and/or pressure of filled Xe gas. The highest in-band EUV energy obtained was 8 mJ per unit solid angle.