Linewidth measurement of table-top EUV laser
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Laser linewidth
Extreme Ultraviolet Lithography
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With the rapid development of extreme ultraviolet (EUV) light sources, such as plasma-based light source and Free Electron Laser (FEL), it provides unprecedented powerful ultra-short EUV radiations. These extremely high intense ultra-short pulses of radiation bring great challenges to the optical components utilized for steering these light beams, especially the radiation damage issues. However, more studies on the EUV damage mechanisms on optical materials are still quite desired because of limited beamtime provided by FEL facilities. In this study, we present a table-top focused EUV optical system built at the Institute of Precision Optical Engineering (IPOE) for performing EUV damage tests on optical materials. This setup consists of a laser-plasma light source, a modified Schwarzschild objective and an EUV energy attenuator. With a large numerical aperture of 0.44 and a demagnification of 11, the Schwarzschild objective is composed of two annular spherical mirrors coated with Mo/Si multilayers. By using the Zirconium filter and Mo/Si multilayers, this setup can generate the focused radiation with an energy density of 2.27 J/cm2 at the wavelength of 13.5 nm on the image plane of the objective with ~8.3 ns pulse duration. The EUV energy can be changed using a gas attenuator by varying the gas pressure of Helium or Nitrogen inside the chamber. The performance and potentials of this setup are demonstrated by the single-shot or multi-shot damage tests on some samples, such as Au thin film, CaF2 and Mo/Si multilayer mirror. The damage thresholds were determined and the possible damage mechanisms are discussed together with available experimental results.
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Extreme Ultraviolet Lithography
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Generation of extreme ultraviolet (EUV) radiation from solid targets is studied and a compact EUV source for small-scale lithographic applications and EUV metrology is development. This source is based on a transfer of conventional x-ray tube technology into the EUV spectral range. As in an ordinary x-ray tube, electrons are generated by a tungesten filament and accelerated in a high-voltage electric field towards a solid target. In the demonstrated "EUV tube" beryllium and silicon targets are used to generate radiation at 11.4 nm and 13.5 nm, respectively. The absolute converstion efficiencies into EUV photons are measured. At 13.5 nm an EUV power of 34μW or 2×1012 photon/s (in 2% bandwidth and a solid angle of 2π sr) is demonstrated. Prospects for a further power scaling of the EUV source are discussed.
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The application of extreme ultraviolet (EUV) lithography in large-scale semiconductor chip manufacturing requires high power EUV radiation sources. The wavelength of the emission should be between 13 and 14 nm according to the 13.4 nm roadmap. To this end, a versatile microwave plasma-based EUV light source type Compact Electron Cyclotron Resonance Ion Source (CECRIS) has been recently built at Lawrence Berkeley National Laboratory (LBNL). In this paper, we present a detailed study of the generation of xenon (Xe) EUV light by the CECRIS using a 1.5 grazing incidence EUV monochromator that has been absolutely calibrated at the advanced Light Source (ALS). For diagnostic purposes, a theoretical study of Xe EUV line emission was performed based on relativistic Hartree-Fock approximation. A major outcome of this work is the absolute calibration of the EUV diagnostic system, which can be used for calibration of other industrial lithography sources.
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In extreme ultraviolet (EUV) lithography, the three-dimensional (3D) structure of the EUV mask, which has an absorber layer and a Mo/Si multilayer on a glass substrate, strongly affects the EUV phase. EUV actinic metrology is required to evaluate the feature of defect printability and the critical dimension (CD) value. The 3D structure modulates the EUV phase, causing the pattern position and focus shift. A microscope that observes in phase contrast necessary. We have developed a coherent EUV scatterometry microscope (CSM) for observing EUV patterns with quantitative phase contrast. The exposure light is coherent EUV light. For the industrial use, we have developed a laboratory coherent source of high-harmonic-generation (HHG) EUV light. High harmonics is pumped by a scale of a Ti:Sapphire laser. In the previous study, a very long exposure time of 1000 s was necessary to detect We upgraded the relay optics. The detection performance of an absorber defect using the new relay optics is We observed the line-end oversize defect and the oversize defect in the 112 nm hole pattern and 180 nm hole pattern. The upgraded system has a detection size limit of a line-end 24-nm-oversize defect with 10 s exposure time, which is 2,688 nm2 (52 × 52 nm2) absorber defect. This result shows high performance capability of HHG-CSM for detecting small defect.
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In this paper we report the development of nanosecond-pulsed fiber laser technology for the next generation EUV lithography sources. The demonstrated fiber laser system incorporates large core fibers and arbitrary optical waveform generation, which enables achieving optimum intensities and other critical beam characteristics on a laser-plasma target. Experiment demonstrates efficient EUV generation with conversion efficiency of up to 2.07% for in-band 13.5-nm radiation using mass-limited Sn-doped droplet targets. This result opens a new technological path towards fiber laser based high power EUV sources for high-throughput lithography steppers.
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The successful implementation of EUV lithography systems strongly relies both on the efficiency of the employed optical components and the precise control of the relevant source parameters. Utilizing a laser-based plasma source for the generation of 13nm radiation, metrology for comprehensive characterization of EUV radiation and the related optics is developed at Laser-Laboratorium Goettingen. A soft X-ray plasma is produced with the help of a Nd:YAG laser which is focused into a pulsed xenon or oxygen gas jet. The alternate use of these two target gases accomplishes either a very intense broadband emission (Xe), or a less intense narrow-band line emission (O2) at the wavelength of 13nm. Additional filtering with the help of Mo/Si mirrors yields quasi-monochromatic 13nm radiation, as needed for testing of optical components, especially reflectometry. The performance of the EUV source is monitored with respect to source diameter, emission characteristics, and 13nm conversion efficiency by the help of different diagnostic tools, including EUV sensitive pin-hole cameras, photo-diodes and an EUV spectrometer. Moreover, first wavefront measurements of EUV radiation are performed with the help of a Hartmann wavefront analyzer, which was sensibilized for 13nm radiation.
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Extreme ultraviolet lithography(EUVL) is being developed worldwide as the next generation technology to be inserted in ~ 2009 for the mass production of IC chips with feature sizes <35 nm. One major challenge to its implementation is the development of a 13.5 nm EUV source of radiation that meets the requirements of current roadmap designs of the source of illumination in commercial EUVL scanners. The light source must be debris-free, in a free-space environment with the imaging EUV optics that must provide sufficient, narrow spectral band EUV power to print 100 wafers/hr. To meet this need, extensive studies on emission from a laser plasma source utilizing tin-doped droplet target was conducted. Presented in this work, are the many optical techniques such as spectroscopy, radiometry, and imaging, that were employed to characterize and optimize emission from the laser plasma source State of the art EUV spectrographs were employed to observe the source's spectrum under various laser irradiation conditions. Comparing the experimental spectra to those from theory, has allowed the determination of the Sn ion stages responsible for emitting into the useful EUV bandwidth. Experimental results were compared to spectral simulations obtained using Collisional-Radiative Equilibrium (CRE) model, as well. Moreover, extensive measurements surveying source emission from 2 nm to 30 nm, which is the region of the electromagnetic spectrum defined as EUV, was accomplished. Absolutely calibrated metrology was employed with the Flying Circus instrument from which the source's conversion efficiency (CE) – from laser to the useful EUV energy – was characterized under various laser irradiation conditions. Hydrodynamic simulations of the plasma expansion together with the CRE model predicted the condition at which optimum conversion could be attained. The condition was demonstrated experimentally, with the highest CE to be slightly above 2%, which is the highest value among all EUV source contenders. In addition to laser intensity, the CE was found to depend on the laser wavelength. For better understanding, this observation is compared to results from simulations. Through a novel approach in imaging, the size of the plasma was characterized by recording images of the plasma within a narrow band, around 13.5 nm. The size, approximately 100 im, is safely within the etendue limit set by the optical elements in the EUV scanner. Finally, the notion of irradiating the target with multiple laser beams was explored for the possibility of improving the source's conversion efficiency.
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The present work, performed in the frame of the EXULITE project, was dedicated to the design and characterization of a laser-plasma-produced extreme ultraviolet (EUV) source prototype at 13.5 nm for the next generation lithography. It was conducted in cooperation with two laboratories from CEA, ALCATEL and THALES. One of our approach originalities was the laser scheme modularity. Six Nd:YAG laser beams were focused at the same time on a xenon filament jet to generate the EUV emitting plasma. Multiplexing has important industrial advantages and led to interesting source performances in terms of in-band power, stability and angular emission properties with the filament jet target. A maximum conversion efficiency (CE) value of 0.44% in 2π sr and 2% band-width was measured, which corresponds to a maximum in band EUV mean power of 7.7 W at a repetition rate of 6 kHz. The EUV emission was found to be stable and isotropic in these conditions.
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Extreme Ultraviolet Lithography
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